Vibration Symptoms Diagnosis and Correction Cadillac Escalade GMT800

Scheme 1

Scheme 2

Diagnostic Starting Point - Vibration Diagnosis and Correction

Important: The following steps must be completed before using the analysis tables or the symptom tables.

1. Perform the Vibration Analysis - Road Testing table before using the other Vibration Analysis tables or the Symptom tables in order to effectively diagnose the customer's concern. The use of Vibration Analysis - Road Testing will first provide duplication of virtually any vibration concern and then identify the correct procedure for diagnosing the area of concern which has been duplicated.
2. Review the following Vibration Diagnostic Process.
3. Review the general descriptions to familiarize yourself with vibration theory and terminology, the J 38792-A, Electronic Vibration Analyzer (EVA) 2 and the J 38792-VS, Vibrate Software. Reviewing this information will help you determine whether the condition described by the customer is a potential operating characteristic or not. Refer to the following: Vibration Theory and Terminology Electronic Vibration Analyzer (EVA) Description and Operation Vibrate Software Description and Operation Reed Tachometer Description

Vibration Diagnostic Process

Important: Using the following steps of the vibration diagnostic process will help you to effectively narrow-down and pin-point the search for the specific source of a vibration concern and to arrive at an accurate repair.

1. Gather specific information on the customer's vibration concern.
2. Perform the road testing steps in sequence as identified in Vibration Analysis - Road Testing in order to duplicate the customer's concern and evaluate the symptoms of the concern under changing conditions. Observe what the vibration feels like and what it sounds like. Observe when the symptoms first appear, when they change, and when they cease.
3. Determine if the customer's vibration concern is truly an abnormal condition or something that is potentially an operating characteristic of the vehicle.
4. Systematically eliminate or "rule-out" possible vehicle systems.
5. Focus diagnostic efforts on the remaining vehicle system and systematically eliminate or "rule-out" possible components of that system.
6. Make a repair on the remaining component, or components, which have not been eliminated systematically, and must therefore be the cause of the vibration.
7. Verify that the customer's concern has been eliminated or at least brought to an acceptable level.
8. Again perform the road testing steps in sequence as identified in Vibration Analysis - Road Testing in order to verify that the vehicle did not have more than one vibration occurring.

Preliminary Visual/Physical Inspection

1. Inspect for aftermarket equipment and modifications which could affect the operation of the vehicle rotating component systems.
2. Inspect the easily accessible or visible components of the vehicle rotating component systems for obvious damage or conditions which could cause the symptom.
3. Inspect the tire inflation pressures for the proper pressure.

Diagnostic Aids

Improper component routing or isolation, or components which are worn or faulty may be the cause of intermittent conditions that are difficult to duplicate. If the vibration concern could not be duplicated by following the steps of the Vibration Diagnostic Process, refer to Vibration Diagnostic Aids.

Test Description

The numbers below refer to the step numbers on the diagnostic table.

Scheme 3

1. 4 Obtaining rotational speed for the components rotating at both tire/wheel speed and propeller shaft speed is critical to systematically eliminating specific vehicle component groups. These component rotational speeds can be generated by using the J 38792-VS, Vibrate Software, or through calculating them manually.
2. 8 Important: Be certain to OBSERVE for disturbances that match the customer's description FIRST, then look at the J 38792-A frequency which corresponds with that disturbance. Proper location of the J 38792-A, electronic vibration analyzer (EVA), sensor onto the component which is most excited by the vibration disturbance is critical to obtaining an accurate frequency reading. This test will duplicate virtually any disturbance which occurs while the vehicle is in motion.
3. 11 Accelerate to a speed high enough above the speed of the disturbance to allow for the time needed to shift into NEUTRAL and for the engine to decrease in RPM to idle speed before coasting down through the disturbance range.
4. 12 This test will either eliminate or confirm the engine as a contributing cause of the customer concern.

Scheme 4

Tire and Wheel Rotational Speed Calculation

A size P235/75R15 tire rotates ONE complete revolution per second (RPS), or 1 Hz, at a vehicle speed of 8 km/h (5 mph). This means that at 16 km/h (10 mph), the same tire will make TWO complete revolutions in one second, 2 Hz, and so on.

Tire Rotational Speed (at 8 km/h [5 mph])

Scheme 5

1. Determine the rotational speed of the tires in revolutions per second (RPS), or Hertz (Hz), at 8 km/h (5 mph), based on the size of the tires. Refer to the Tire Rotational Speed table. For example: According to the Tire Rotational Speed table, a P255/70R16 tire makes 0.96 revolutions per second (Hz) at a vehicle speed of 8 km/h (5 mph). This means that for every increment of 8 km/h (5 mph) in vehicle speed, the tire's rotation increases by 0.96 revolutions per second (Hz).
2. Determine the number of increments of 8 km/h (5 mph) that are present, based on the vehicle speed (km/h, mph) at which the disturbance occurs. For example: Assume that a disturbance occurs at a vehicle speed of 96 km/h (60 mph). A speed of 96 km/h (60 mph) has 12 INCREMENTS of 8 km/h (5 mph): 96 km/h (60 mph) divided by 8 km/h (5 mph) = 12 increments
3. Determine the rotational speed of the tires in revolutions per second (Hz), at the specific vehicle speed (km/h, mph) at which the disturbance occurs. For example: To determine the tire rotational speed at 96 km/h (60 mph), multiply the number of increments of 8 km/h (5 mph) by the revolutions per second (Hz) for one increment: 12 (increments) X 0.96 Hz = 11.52 Hz (rounded to 12 Hz)
4. Compare the rotational speed of the tires at the specific vehicle speed at which the disturbance occurs, to the dominant frequency recorded on the J 38792-A during testing. If the frequencies match, then a first-order disturbance related to the rotation of the tire/wheel assemblies is present. If the frequencies do not match, then the disturbance may be related to a higher order of tire/wheel assembly rotation.
5. To compute higher order tire/wheel assembly rotation related disturbances, multiply the rotational speed of the tires at the specific vehicle speed at which the disturbance occurs, by the order number: 12 Hz X 2 (for second order) = 24 Hz second-order tire/wheel assembly rotation related 12 Hz X 3 (for third order) = 36 Hz third-order tire/wheel assembly rotation related If any of these computations match the frequency of the disturbance, a disturbance of that particular order, relating to the rotation of the tire/wheel assemblies is present.

Propeller Shaft Rotational Speed Calculation

1. Determine the first order rotational speed of the propeller shaft(s) in revolutions per second (Hz), based on the first-order rotational speed of the tire/wheel assemblies and the drive axle(s) (final drive) ratio(s). 12 Hz X 3.42 drive axle (final drive) ratio = 41.04 Hz (rounded to 41 Hz) first-order propeller shaft rotation related
2. Compare the rotational speed of the propeller shaft(s) at the specific vehicle speed at which the disturbance occurs, to the dominant frequency recorded on the J 38792-A during testing. If the frequencies match, then a first-order disturbance related to the rotation of the propeller shaft is present. If the frequencies do not match, then the disturbance may be related to the second-order of propeller shaft rotation.
3. To compute a second order propeller shaft rotation related disturbance, multiply the first order rotational speed of the propeller shaft at the specific vehicle speed at which the disturbance occurs, by the order number of 2: 41 Hz X 2 (for second order) = 82 Hz second-order propeller shaft rotation related If the computation matches the frequency of the disturbance, a disturbance relating to the second-order rotation of the propeller shaft is present.

Component Rotational Speed Worksheet

Utilize the following worksheet as an aid in calculating the first, second and third order of tire/wheel assembly rotational speed and the first and second order of propeller shaft rotational speed related disturbances that may be present in the vehicle.

If after completing the Tire/Wheel Rotation Worksheet, the frequencies calculated do NOT match the dominant frequency of the disturbance recorded during testing, either recheck the data, or attempt to rematch the figures allowing for 11/2-8 km/h (1-5 mph) of speedometer error.

If the possible tire/wheel assembly and/or propeller shaft rotational speed related frequencies still do not match the dominant frequency of the disturbance, the disturbance is most likely torque/load sensitive.

If after completing the Tire/Wheel Rotation Worksheet, one of the frequencies calculated DOES match the dominant frequency of the disturbance, the disturbance is related to the rotation of that component group, (tire/wheel assembly or propeller shaft).

Scheme 6

The numbers below refer to the step numbers in the diagnostic table

Scheme 7

1. 4 A buildup of foreign material on a tire and wheel assembly and/or a damaged, abnormally or excessively worn tire and wheel assembly could cause a vibration disturbance.
2. 6 Tire and wheel assemblies that exhibit excessive runout when measured while mounted on the vehicle, may or may not be contributing to, or causing a vibration disturbance. On-vehicle runout, if present, could contribute to, or cause a vibration disturbance, but the cause of the on-vehicle runout may not be the tire and wheel assemblies.
3. 7 Tire and wheel assemblies that exhibit excessive runout when measured off of the vehicle could cause a vibration disturbance.
4. 8 Tire and wheel assemblies that exhibit marginal runout (within acceptable limits, but close to the maximum) when measured off of the vehicle could still be contributing to a vibration disturbance, if its mating hub/axle flange also exhibits marginal runout. When the tire and wheel assembly and the hub axle flange are mounted to each other, the combined stack-up of their marginal amounts of runout could combine to produce an excessive amount of runout, which could cause a vibration disturbance.
5. 13 Brake rotors that exhibit excessive imbalance could contribute to, or possibly cause a vibration disturbance.
6. 14 A hub/axle flange and/or wheel studs that exhibit excessive runout could cause a vibration disturbance.
7. 15 When the tire and wheel assembly and the hub axle flange are mounted to each other, the combined stack-up of their marginal amounts of runout could combine to produce an excessive amount of runout, which could cause a vibration disturbance. Match-mounting or vectoring the tire and wheel assembly to the hub/axle flange will modify the amount of combined runout.
8. 19 Force variation may be present in a tire and wheel assembly that exhibited acceptable balance and runout. Force variation, if present, could contribute to, or cause a vibration disturbance.
9. 21 Vibration disturbances could be affected by, or possibly caused by, components that are susceptible to steering input and/or torque-load input.
10. 23 On-vehicle balancing, or finish-balancing can be used to reduce small amounts of imbalance which may be present as a result of the combined stack-up of the tire and wheel assembly with other components which may exhibit marginal balance.

Scheme 8

The numbers below refer to the step numbers in the diagnostic table.

Scheme 9

1. 8 First-order driveline related vibrations are usually caused by components that exhibit excessive runout or imbalance. Reproducing a vibration concern in the service stall can aid in pin-pointing the component which may be at fault. (A vibration concern may appear to be either less severe or more severe when duplicated in a service stall, than when duplicated on the road.)
2. 9 First-order driveline related vibrations that could not be duplicated during the non-torque sensitive service stall test, could be caused by internal axle components. This test is designed to duplicated first-order driveline related vibrations that are sensitive to torque/load. (A vibration concern may appear to be either less severe or more severe when duplicated in a service stall, than when duplicated on the road.)
3. 11 First-order driveline vibrations can be caused by excessive runout of a propeller shaft.
4. 15 First-order driveline vibrations can be caused by excessive runout of the pinion flange. If a propeller shaft exhibits excessive runout at a pinion flange end only, the runout may actually be caused by the pinion flange.
5. 17 Re-indexing a propeller shaft to a pinion flange can reduce the amount of total combined runout which the components produce, which may in-turn reduce a vibration.

Scheme 10

The numbers below refer to the step numbers on the diagnostic table

Scheme 11

1. 2 This test will determine the effect of turning input on the vibration.
2. 6 This test will determine the effect of an initial heavy torque load on the vibration.
3. 7 Damaged or worn wheel drive shafts may cause a noise or vibration that may be transferred into the passenger compartment.
4. 9 Damaged or worn wheel bearings may cause a noise or vibration that may be transferred into the passenger compartment.
5. 10 Damaged or worn suspension components may cause a noise or vibration that may be transferred into the passenger compartment.
6. 11 Damaged or worn engine, transmission, and/or exhaust mounts may cause a noise or vibration that may be transferred into the passenger compartment.
7. 12 Incorrect trim height may cause binding and/or interference between components that may produce a vibration.

Scheme 12

The numbers below refer to the step numbers on the diagnostic table.

Scheme 13

1. 2 If powertrain related DTCs are present, there may be a powertrain performance condition present which could be a contributing cause to the customer's concern.
2. 3 This step is designed to identify engine-speed related disturbances that are NOT torque or load sensitive.
3. 4 This step is designed to identify engine-speed related disturbances that ARE torque or load sensitive.
4. 6 Making comparisons of the customer's vehicle with an equally equipped, same model year and type, KNOWN GOOD vehicle will help determine if certain disturbances may be characteristic of a vehicle design.

Scheme 14

Engine First Order Classification

1. Convert the engine speed in revolutions per minute (RPM), recorded during duplication of the disturbance into Hertz, revolutions per second (RPS), by dividing the RPM by 60 seconds. Refer to the following example: 1,200 RPM divided by 60 = 20 Hz (or RPS)
2. Compare the dominant frequency in Hz, recorded during duplication of the disturbance with the engine speed just converted into Hz, to determine if they are related.
3. If the dominant frequency in Hz, recorded during duplication of the disturbance and the engine speed, converted into Hz, ARE related, then an engine FIRST ORDER related disturbance is present. Engine first order disturbances are usually related to an imbalance component. Refer to the Engine Order Related Disturbances table.
4. If the dominant frequency in Hz, recorded during duplication of the disturbance and the engine speed, converted into Hz, are NOT related, then determine if the disturbance is related to the engine's firing frequency. Proceed to Engine Firing Frequency Classification.

Engine Firing Frequency Classification

Engine firing frequency is a term used to describe the number of firing pulses (one firing pulse = one cylinder firing) that occur during ONE complete revolution of the crankshaft, multiplied by the number of crankshaft revolutions per second, Hz.

1. Calculate the engine firing frequency. To determine the firing frequency of a 4-stroke engine during ONE complete revolution of the crankshaft, multiply the engine speed, converted into Hz, by HALF of the total number of cylinders in the engine. For example: The engine speed, converted into Hz, was 20 Hz; if the vehicle was equipped with a V8 engine, 4 of the 8 cylinders would actually fire during ONE complete revolution of the crankshaft. Multiply the converted engine speed (20 Hz) by 4 cylinders firing. 20 Hz X 4 = 80 Hz The engine firing frequency for a V8 engine at the original engine speed of 1,200 RPM, recorded during duplication of the disturbance, would be 80 Hz. In like manner, a 6-cylinder engine would have a firing frequency of 60 Hz at the same engine speed of 1,200 RPM. 20 Hz X 3 = 60 Hz
2. Compare the dominant frequency in Hz, recorded during duplication of the disturbance with the engine firing frequency in Hz, just calculated, to determine if they are related.
3. If the dominant frequency in Hz, recorded during duplication of the disturbance and the engine firing frequency in Hz, just calculated ARE related, then an engine FIRING FREQUENCY related disturbance is present. Engine firing frequency disturbances are usually related to improper isolation of a component. Refer to the Engine Order Related Disturbances table.
4. If the dominant frequency in Hz, recorded during duplication of the disturbance and the engine firing frequency in Hz, just calculated are NOT related, then determine if the disturbance is related to another engine order classification. Proceed to Other Engine Order Classification.

Other Engine Order Classification

1. Multiply the engine speed, converted into Hz, recorded during duplication of the disturbance by different possible order-numbers, other than 1 (first order) or the number used to determine the firing frequency of the engine.
2. Compare the dominant frequency in Hz, recorded during duplication of the disturbance with the other possible engine orders just calculated, to determine if they are related.
3. If the dominant frequency in Hz, recorded during duplication of the disturbance and one of the other engine order frequencies in Hz, just calculated ARE related, then an engine related disturbance of that order is present. If an engine related disturbance is present that is NOT related to first order or firing frequency, then it could be related to an engine driven accessory system. Proceed to Engine Driven Accessories Related to Engine Order.

Engine Driven Accessories Related to Engine Order

Engine driven accessory systems can be related to specific engine orders depending upon the relationship of the accessory pulley diameter to the crankshaft pulley diameter. For example

1. If the crankshaft pulley measured 20 cm (8 in) in diameter and one of the engine driven accessory pulleys measured 10 cm (4 in) in diameter, then that accessory pulley would rotate 2 times for every one rotation of the crankshaft pulley. If that accessory system was not isolated properly, or was not operating properly, it would be identifiable as a 2nd order engine related disturbance.
2. In like manner, if an engine driven accessory pulley measured 5 cm (2 in) in diameter, then that accessory pulley would rotate 4 times for every one rotation of the crankshaft pulley. If that accessory system was not isolated properly, or was not operating properly, it would be identifiable as a 4th order engine related disturbance.

Engine driven accessories that contribute to, are excited by, or are the sole cause of a disturbance are usually doing so because of improper isolation that causes a transfer path into the passenger compartment or to another major component of the vehicle body.

Using the J 38792-VS, Vibrate Software, accurately measuring the diameters of the accessory pulleys and the crankshaft pulley, and performing the appropriate diagnostic procedures completely will lead to the specific accessory system which is either contributing to, or causing the customer's concern.

Scheme 15

The numbers below refer to the step numbers on the diagnostic table.

1. 4 A loose, damaged, misaligned, or defective powertrain insulator and/or bracket may create a transfer path into the passenger compartment.
2. 6 A loose, damaged, misaligned, or defective exhaust system insulator and/or bracket may create a transfer path into the passenger compartment.
3. 8 Incorrectly seated and/or aligned powertrain components and/or exhaust system components may create a transfer path into the passenger compartment. When loosening powertrain mounts in order to re-bed the powertrain observe the following: Do not loosen the mount bracket-to-engine bolts/nuts, do not loosen the mount bracket-to-vehicle frame bolts/nuts if mount brackets are used. Loosen the mount-to-mount bracket bolts/nuts if mount brackets are used, or loosen the mount-to-slotted holes in vehicle frame bolts/nuts if a direct-mount design is used.
4. 9 Non-rotating engine driven accessory component systems can no longer produce a unique disturbance.
5. 10 Non-rotating engine driven accessory components can no longer produce a unique disturbance. If a disturbance is still present, but the characteristics have been altered, it is possible that these component systems are acting as a transfer path for engine firing frequency or a first order engine disturbance. If a disturbance is still present, but the characteristics have NOT been altered, it is NOT likely that these component systems are acting as a transfer path for engine firing frequency or a first order engine disturbance.
6. 11 If the mark placed on the face of an engine driven accessory seems to stand still while running this test, then that accessory system is either responding to an existing frequency (such as engine firing pulses), or creating a disturbance.
7. 12 A loose, damaged, misaligned, or defective engine driven accessory system insulator and/or bracket may create a transfer path into the passenger compartment.
8. 13 Removing the engine driven accessory and bracket(s) from the engine allows a thorough inspection to determine if any conditions are present that may create a transfer path into the passenger compartment.

Scheme 16

Scheme 17

Scheme 18

Scheme 19

Scheme 20

The numbers below refer to the step numbers on the diagnostic table.

Scheme 21

1. 2 If sufficient clearance exists to separate the transmission torque converter from the engine flywheel/flexplate, then further tests can be used to isolate the transmission from the engine.
2. 3 An engine flywheel/flexplate that has excessive lateral runout, when combined with the mass of the transmission torque converter, can produce a disturbance.
3. 4 An engine flywheel/flexplate that is loose at the engine crankshaft or that is cracked or damaged, when combined with the mass of the transmission torque converter, can produce a disturbance.
4. 5 This step is designed to isolate the transmission from the engine to determine if the disturbance is related to the engine ONLY.
5. 7 Re-indexing the transmission torque converter to the engine flywheel/flexplate alters the balance relationship between the torque converter and the rear of the engine.
6. 9 Placing the J 38792-A sensor onto the underside of the engine oil pan along the FRONT and the REAR edge allows for a determination to be made, which will help to narrow down the cause of the disturbance.
7. 10 An engine flywheel/flexplate that is damaged, misaligned, and/or imbalance, can produce a disturbance.
8. 11 An engine crankshaft (harmonic) balancer that is damaged, misaligned, and/or imbalance, can produce a disturbance.

Scheme 22

Vibration Diagnostic Aids

Vibration Diagnostic Aids - Vibration Intermittent or Not Duplicated

Important: If you have not completed the Vibration Analysis tables as indicated and reviewed Vibration Diagnostic Aids, refer to Vibration Diagnostic Aids BEFORE proceeding.

If you have not been able to duplicate the vibration concern or have only been able to duplicate the concern intermittently, review the following information.

Most vibration concerns that cannot be duplicated are due to either specific conditions that are not present during the duplicating attempts, or due to not following the procedures designed to duplicate concerns properly and in the sequence indicated.

Specific Conditions Can Affect the Condition

Consider the following conditions which may not have been present while attempts were made to duplicate the vibration concern. Attempt to obtain more specific information from the customer as to the EXACT conditions that are present when they experience the vibration which they are concerned about. Attempt to duplicate the vibration concern again while recreating the EXACT conditions necessary, except those which pose a safety concern or are outside the boundaries of normal operating conditions, such as loading the vehicle beyond its designed weight ratings, etc.

Most attempts to duplicate a vibration concern are made after the vehicle has been driven to the dealership and perhaps even sat inside the building for a time; the vehicle may be too warm to detect the concern during duplication efforts. The opposite could also occur; perhaps the vehicle has sat out in the cold for a time and fails to reach full operating temperatures during attempts to duplicate the concern.

Flat Spots on Tires

Tires which have sat and been cool for a time can develop flat spots.

Irregular Wear on Tire Treads

Tires which have sat and been cool for a time will be stiffer and any irregular wear conditions will be more noticeable than they will be once the tires have warmed and softened.

Exhaust System Growth

Exhaust systems may exhibit a ground-out condition when cool which goes away once the system hot. The opposite may be true that the exhaust system is fine when cool but a ground-out condition occurs once the system reaches operating temperatures. Exhaust systems can grow by 21/2-5 cm (1-2 in) when hot.

Engine-Driven Accessory Noises

1. Belt Whipping An engine accessory drive belt, or belts could exhibit a whipping condition if a belt is deteriorating and deposits are building up on the underside of the belt.
2. Loose Mounting Brackets or Component Ground-Out Engine-driven accessories such as a generator, a power steering pump, or an air conditioning compressor could exhibit noise conditions due to either loose mounting brackets or due to related components of the system in a ground-out condition during certain operation of that accessory system.
3. Cold or Hot These accessories could exhibit noise conditions when cool which go away once they are fully warmed-up, or the opposite may be true.
4. Load on an Accessory Component These accessories could exhibit a noise condition while under a heavy load - perhaps when combined with a cool or fully warmed-up condition.
5. Bent or Misaligned Pulleys Bent or mis-aligned pulleys in one or more engine-driven accessory systems could contribute to a noise or vibration condition.
6. Fluid Level in Accessory Systems These accessories could exhibit a noise condition due to an abnormal amount of fluid contained in the system of which the accessory is a part.
7. An improper power steering fluid level could produce noises in the power steering system.
8. An improper air conditioning refrigerant level or an excessive amount of refrigerant oil could produce noises or possibly vibrations in the air conditioning system.
9. Incorrect Fluid Type in Accessory Systems These accessories could exhibit a noise condition due to the incorrect type of fluid contained in the system of which the accessory is a part.

Vehicle Payload

The vibration concern may only occur when the vehicle is carrying heavy payloads or towing a trailer; the vehicle may have been empty during duplication efforts.

Heavy Payload

The vehicle may have been empty during attempts to duplicate the vibration concern, but the customer may actually experience the vibration concern while the vehicle is carrying a large payload.

Trailer Towing

The customer may experience the vibration concern only while towing a trailer.

Roadway Selection

The selection of roadways used to perform the vibration duplication procedures is likely to be in the near vicinity of the dealership and may not provide a road surface that is close enough to the surface on which the customer usually drives the vehicle.

The customer may only experience the vibration on a particular roadway. Perhaps the roadway is overly crowned or is very bumpy or rough.

Vibration Diagnostic Aids - Vibration Duplicated, Component Not Identified

Aftermarket Add-On Accessories

Aftermarket accessories which have been added to the vehicle can actually transmit and magnify INHERENT component rotational frequencies, if the accessories were not installed correctly.

An accessory should be installed in such a way that it is isolated from becoming a possible transfer path into the rest of the vehicle. For example, if a set of running boards has been installed improperly and they are sensitive to a particular frequency of a rotating component, the running boards could begin to respond to the frequency and actually create a disturbance once the amplitude of the frequency reaches a high enough point, probably at a higher vehicle speed.

If the same set of running boards were installed properly - isolated properly - the transfer path would be removed and the disturbance would no longer be present.

Vibration Diagnostic Aids - Vibration Duplicated, Difficult to Isolate/Balance Component

Driveline Torque-Load Conditions

An axle differential that has internal conditions such as excessive runout of components, misalignment of components, imbalance, etc., can produce vibration concerns which may be transmitted into the propeller shaft(s). This sort of a vibration occurrence can increase or decrease in severity based primarily upon torque-load, but can also be affected by cold or hot conditions.

The propeller shaft and other related components may or may not pass inspections for wear or damage, runout, alignment, etc., depending upon whether there is only one vibration source or more than one.

Difficult to System Balance the Driveline

If after following the Vibration Analysis - Driveline table you were instructed to system balance the driveline and you experienced difficulty in doing so while CAREFULLY following the procedures indicated (the EVA strobe readings seem to keep changing), then the axle differential to which the propeller shaft is attached should be suspected to have internal problems which are being transmitted to the propeller shaft. Refer to Diagnostic Starting Point - Front Drive Axle in Front Drive Axle, or to Diagnostic Starting Point - Rear Drive Axle in Rear Drive Axle, for internal axle diagnostics.

Vibration Diagnostic Aids - Vibration Duplicated, Appears to Be Potential Operating Characteristic

Check Service Bulletins

If BOTH of the following statements are TRUE, then check service bulletins for the condition identified. If the condition has already been identified and investigated prior to this vehicle, and has been determined to be something that is not truly an operating characteristic or that perhaps is not design-intent, there will likely be adjustments or corrections identified which will address the condition.

1. You CAREFULLY followed the steps indicated through reviewing the Diagnostic Starting Point - Vibration Diagnosis and completing the Vibration Analysis tables identified and you have duplicated the vibration concern.
2. You have come to the conclusion through comparison with a very equally-equipped, same model year and type, KNOWN GOOD vehicle that the customer's concern is a condition that appears to be a potential operating characteristic of the vehicle.

Symptoms - Vibration Diagnosis and Correction

Table 1: Vibration Symptoms that are Felt

Table 2: Vibration Symptoms that are Heard

Symptom Tables

Refer to a Vibration Analysis table as indicated in the following symptom tables, based on the most dominant characteristic(s) of the customer's vibration concern (felt or heard) that is evident during the appropriate condition of the occurrence.

Scheme 23

Scheme 24

Vehicle-to-Vehicle Diagnostic Comparison

Comparing the customer's vehicle to a KNOWN GOOD vehicle that is essentially identical will help determine if the customer's concern may be characteristic of a vehicle design. To arrive at a valid conclusion, the comparison must be performed under the same conditions, using the same criteria, on a vehicle that has the same option content as the customer's vehicle.

The comparison vehicle must match the customer's vehicle in the following areas

1. Year
2. Make
3. Model
4. Body style
5. Powertrain configuration
6. Driveline configuration
7. Final drive ratio
8. Tire/wheel size and type
9. Suspension package
10. Trailering package
11. GVW rating
12. Performance options
13. Luxury options

Scheme 25

The tires on all new production models have a tire performance criteria (TPC) rating number molded on the sidewall. The TPC rating will appear as a 4-digit number preceded by the letters TPC SPEC on the tire wall near the tire size. A replacement tire should have the same TPC rating.

Scheme 26

Inspect the tire and wheel assemblies for the following conditions

1. Unusual wear such as cupping, flat spots, and/or heel-and-toe wear These conditions can cause tire growl, tire howl, slapping noises, and/or vibrations throughout the vehicle.
2. Proper inflation to specifications for the vehicle
3. Bulges in the sidewalls Do not confuse bulges, which are an abnormal condition, with normal ply splices which are commonly seen as indentations in the sidewall.
4. Bent rim flanges

Scheme 27

Scheme 28

1. Raise and support the vehicle. Refer to Lifting and Jacking the Vehicle in General Information.
2. Closely inspect each tire for proper and even bead seating.
3. If any of the tire beads were not properly or evenly seated, reseat the tire bead, then proceed to step 4. Refer to Tire Mounting and Dismounting in Tires and Wheels.
4. Wrap the circumference of each tire with tape (1) in the center tread area. Wrapping the tread with tape allows for a smooth and accurate reading of radial runout to be obtained.
5. Position the dial indicator on the taped portion of the tire tread such that the dial indicator is perpendicular to the tire tread surface.
6. Slowly rotate the tire and wheel assembly one complete revolution in order to find the low spot.
7. Set the dial indicator to zero at the low spot.
8. Slowly rotate the tire and wheel assembly one more complete revolution and measure the total amount of radial runout. Specification Maximum tire and wheel assembly radial runout - measured on-vehicle: 1.52 mm (0.060 in)
9. Position the dial indicator on a smooth portion of the tire sidewall, as close to the tread as possible, such that the dial indicator is perpendicular to the tire sidewall surface.
10. Slowly rotate the tire and wheel assembly one complete revolution in order to find the low spot. Ignore any jumps or dips due to sidewall splices.
11. Set the dial indicator to zero at the low spot.
12. Slowly rotate the tire and wheel assembly one more complete revolution and measure the total amount of lateral runout. Ignore any jumps or dips due to sidewall splices and attain an average runout measurement. Specification Maximum tire and wheel assembly lateral runout - measured on-vehicle: 1.52 mm (0.060 in)
13. Repeat steps 4 through 12 until all of the tire and wheel assembly radial and lateral runout measurements have been taken.
14. Lower the vehicle.

Scheme 29

Scheme 30

Scheme 31

Scheme 32

1. Raise and support the vehicle. Refer to Lifting and Jacking the Vehicle in General Information.
2. Mark the location of the wheels to the wheel studs and mark the specific vehicle position on each tire and wheel - LF, LR, RF, RR.
3. Remove the tire and wheel assemblies from the vehicle. Refer to Tire and Wheel Removal and Installation in Tires and Wheels.
4. Closely inspect each tire for proper and even bead seating.
5. If any of the tire beads were not properly or evenly seated, reseat the tire bead, then proceed to step 6. Refer to Tire Mounting and Dismounting in Tires and Wheels.
6. Mount a tire and wheel assembly on a spin-type wheel balancer. Locate the tire and wheel assembly on the balancer with a cone through the back side of the center pilot hole.
7. Wrap the outer circumference of each tire with tape (1) in the center tread area. Wrapping the tread with tape allows for a smooth and accurate reading of radial runout to be obtained.
8. Position the dial indicator on the taped portion of the tire tread such that the dial indicator is perpendicular to the tire tread surface.
9. Slowly rotate the tire and wheel assembly one complete revolution in order to find the low spot.
10. Set the dial indicator to zero at the low spot.
11. Slowly rotate the tire and wheel assembly one more complete revolution and measure the total amount of radial runout. Specification Maximum tire and wheel assembly radial runout - measured off-vehicle: 1.27 mm (0.050 in)
12. Position the dial indicator on a smooth portion of the tire sidewall, as close to the tread as possible, such that the dial indicator is perpendicular to the tire sidewall surface.
13. Slowly rotate the tire and wheel assembly one complete revolution in order to find the low spot. Ignore any jumps or dips due to sidewall splices.
14. Set the dial indicator to zero at the low spot.
15. Slowly rotate the tire and wheel assembly one more complete revolution and measure the total amount of lateral runout. Ignore any jumps or dips due to sidewall splices and attain an average runout measurement. Specification Maximum tire and wheel assembly lateral runout - measured off-vehicle: 1.27 mm (0.050 in)
16. Repeat steps 6 through 15 until all of the tire and wheel assembly radial and lateral runout measurements have been taken.
17. If ANY of the tire and wheel assembly runout measurements were NOT within specifications, proceed to step 19 .
18. If ALL of the tire and wheel assembly runout measurements WERE within specifications, then the off-vehicle tire and wheel assembly runout is considered acceptable.
19. Position the dial indicator on the horizontal outer surface of the wheel rim flange - with the tire still mounted - such that the dial indicator is perpendicular to the rim flange surface. Wheel runout should be measured on both the inboard and outboard rim flanges, unless wheel design will not permit. Ignore any jumps or dips due to paint drips, chips, or welds.
20. Slowly rotate the tire and wheel assembly one complete revolution in order to find the low spot.
21. Set the dial indicator to zero at the low spot.
22. Slowly rotate the tire and wheel assembly one more complete revolution and measure the total amount of wheel radial runout. Specification Maximum aluminum wheel radial runout - measured off-vehicle, tire mounted: 0.762 mm (0.030 in) Maximum steel wheel radial runout - measured off-vehicle, tire mounted: 1.015 mm (0.040 in)
23. Position the dial indicator on the vertical outer surface of the wheel rim flange - with the tire still mounted - such that the dial indicator is perpendicular to the rim flange surface. Wheel runout should be measured on both the inboard and outboard rim flanges, unless wheel design will not permit. Ignore any jumps or dips due to paint drips, chips, or welds.
24. Slowly rotate the tire and wheel assembly one complete revolution in order to find the low spot.
25. Set the dial indicator to zero at the low spot.
26. Slowly rotate the tire and wheel assembly one more complete revolution and measure the total amount of wheel lateral runout. Specification Maximum aluminum wheel lateral runout - measured off-vehicle, tire mounted: 0.762 mm (0.030 in) Maximum steel wheel lateral runout - measured off-vehicle, tire mounted: 1.143 mm (0.045 in)
27. Repeat steps 19 through 26 until all of the wheel radial and lateral runout measurements have been taken on each of the - tire and wheel - assemblies with assembly runout measurements which were NOT within specifications.
28. If any of the wheel runout measurements were NOT within specifications, proceed to Measuring Wheel Runout - Tire Dismounted.
29. For any of the wheel runout measurements which WERE within specifications, while the - tire and wheel - assembly runout measurements were NOT within specifications, replace the tire, then balance the assembly. Refer to Tire and Wheel Assembly Balancing - Off-Vehicle.
30. After replacement of any tires, always remeasure the runout of the affected tire and wheel assembly, or assemblies.
31. Using the matchmarks made prior to removal, install the tire and wheel assemblies to the vehicle. Refer to Tire and Wheel Removal and Installation in Tires and Wheels.
32. Lower the vehicle.

Scheme 33

Scheme 34

1. On the tire and wheel assembly, or assemblies with wheel runout measurements - tire mounted - which were NOT within specifications, mark each tire and wheel in relation to each other.
2. Dismount the tire from the wheel. Refer to Tire Mounting and Dismounting in Tires and Wheels.
3. Mount the wheel on a spin-type wheel balancer.
4. Locate the wheel on the balancer with a cone through the back side of the center pilot hole.
5. Position the dial indicator on the horizontal inner surface of the wheel rim flange - with the tire dismounted - such that the dial indicator is perpendicular to the rim flange surface. Wheel runout should be measured on both the inboard and outboard rim flanges. Ignore any jumps or dips due to paint drips, chips, or welds.
6. Slowly rotate the wheel one complete revolution in order to find the low spot.
7. Set the dial indicator to zero at the low spot.
8. Slowly rotate the wheel one more complete revolution and measure the total amount of wheel radial runout. Specification Maximum aluminum wheel radial runout - measured off-vehicle, tire dismounted: 0.762 mm (0.030 in) Maximum steel wheel radial runout - measured off-vehicle, tire dismounted: 1.015 mm (0.040 in)
9. Position the dial indicator on the vertical inner surface of the wheel rim flange - with the tire dismounted - such that the dial indicator is perpendicular to the rim flange surface. Wheel runout should be measured on both the inboard and outboard rim flanges. Ignore any jumps or dips due to paint drips, chips, or welds.
10. Slowly rotate the wheel one complete revolution in order to find the low spot.
11. Set the dial indicator to zero at the low spot.
12. Slowly rotate the wheel one more complete revolution and measure the total amount of wheel lateral runout. Specification Maximum aluminum wheel lateral runout - measured off-vehicle, tire dismounted: 0.762 mm (0.030 in) Maximum steel wheel lateral runout - measured off-vehicle, tire dismounted: 1.143 mm (0.045 in)
13. Repeat steps 2 through 12 until all of the wheel radial and lateral runout measurements - tire dismounted - have been taken on each wheel with runout measurements - tire mounted - which were NOT within specifications.
14. If any of the wheel runout measurements - tire dismounted - were NOT within specifications, replace the wheel. Always measure the runout of any replacement wheels.
15. For any of the wheel runout measurements which WERE within specifications, while the - tire and wheel - assembly runout measurements were NOT within specifications, replace the tire, then balance the assembly. Refer to Tire and Wheel Assembly Balancing - Off-Vehicle.
16. Using the matchmarks made prior to dismounting the tire, or tires, mount the tire, or tires to the wheel, or wheels, then balance the assembly, or assemblies. Refer to Tire and Wheel Assembly Balancing - Off-Vehicle. Always measure the runout of any of the tire and wheel assemblies which have had the tires dismounted and mounted.
17. Using the matchmarks made prior to removal, install the tire and wheel assemblies to the vehicle. Refer to Tire and Wheel Removal and Installation in Tires and Wheels.
18. Lower the vehicle.

Scheme 35

1. Support the vehicle drive axle(s) on a suitable hoist. Refer to Lifting and Jacking the Vehicle in General Information.
2. Remove the tire and wheel assemblies from the drive axle(s). Refer to Tire and Wheel Removal and Installation in Tires and Wheels. CAUTION: Refer to «WORK STALL TEST CAUTION»(/cadillac/escalade/gmt800-2001-2006/remont/oem-general-information/#gm-vehicles-cautions-notices__work-stall-test-caution) in Cautions and Notices.
3. Reinstall the wheel nuts in order to retain the brake rotors.
4. Run the vehicle at the concern speed while inspecting for the presence of the vibration. NOTE: Do not depress the brake pedal with the brake rotors and/or the brake drums removed, or with the brake calipers repositioned away from the brake rotors, or damage to the brake system may result.
5. If the vibration is still present, remove the brake rotors from the drive axle(s), then run the vehicle back to the concern speed. Refer to Brake Rotor Replacement - Front and Brake Rotor Replacement - Rear in Disc Brakes.
6. If the vibration is eliminated when the brake rotors are removed from the drive axle(s), repeat the test with one rotor installed at a time. Replace the rotor that is causing or contributing to the vibration concern. Refer to Brake Rotor Replacement - Front and Brake Rotor Replacement - Rear in Disc Brakes.
7. If a brake rotor was replaced as a result of following the previous steps, or if necessary to confirm the results obtained during the previous steps, and/or to check the non-drive axle components, perform the following: Mount the brake rotor on a balancer in the same manner as a tire and wheel assembly. Important: Check brake rotors for static imbalance only; ignore the dynamic imbalance readings. Inspect the rotor for static imbalance.

There is not a set tolerance for brake rotor static imbalance. (However, any brake rotor measured in this same manner which is over 21 g [3/4 oz] may have the potential to cause or contribute to a vibration.) Rotors suspected of causing or contributing to a vibration should be replaced. Any rotor that is replaced should be checked for imbalance in the same manner.

Tools Required

J 8001 Dial Indicator Set, or equivalent

Scheme 36

Scheme 37

1. Raise and suitably support the vehicle. Refer to Lifting and Jacking the Vehicle in General Information.
2. Mark the location of the wheels to the wheel studs and mark the specific vehicle position on each tire and wheel (LF, LR, RF, RR).
3. Remove the tire and wheel assemblies from the vehicle. Refer to Tire and Wheel Removal and Installation in Tires and Wheels.
4. Remove the brake rotors from the vehicle, except for full floating type rear drive axles. Refer to Brake Rotor Replacement - Front and Brake Rotor Replacement - Rear in Disc Brakes.
5. Remove any loose debris or corrosion from the hub/axle flange surface.
6. Position the J 8001, or equivalent, on the machined surface of the wheel hub/axle flange (or brake rotor on full-floating axles) outside of the wheel studs.
7. Rotate the hub one complete revolution in order to find the low spot.
8. Set the J 8001, or equivalent, to zero at the low spot.
9. Rotate the hub one more complete revolution and measure the total amount of wheel hub/axle flange runout. Specification (Guideline) Wheel hub/axle flange runout tolerance guideline: 0.132 mm (0.005 in)
10. If the runout of the wheel hub/axle flange IS within specification, proceed to step 13 .
11. If the runout of the wheel hub/axle flange is marginal, the wheel hub may or may not be the source of the disturbance.
12. If the runout of the wheel hub/axle flange is excessive, replace the wheel hub/axle flange. Measure the runout of the new wheel hub/axle flange. Refer to the appropriate procedure: Wheel Hub, Bearing, and Seal Replacement in Front Suspension Rear Axle Shaft Replacement in Rear Drive Axle
13. Position the J 8001, or equivalent, in order to contact the wheel mounting studs. Measure the stud runout as close to the flange as possible.
14. Turn the hub one complete revolution to register on each of the wheel studs.
15. Zero the J 8001, or equivalent, on the lowest stud.
16. Rotate the hub one more complete revolution and measure the total amount of wheel stud (stud circle) runout. Specification (Guideline) Wheel stud runout tolerance guideline: 0.254 mm (0.010 in)
17. If the runout of the wheel studs (stud circle) is marginal, the wheel studs may or may not be contributing to the disturbance.
18. If the runout of the wheel studs (stud circle) is excessive, replace the wheel studs as necessary. Measure the runout of the new wheel studs. Refer to the appropriate procedure: Wheel Stud Replacement in Front Suspension Wheel Stud Replacement in Rear Suspension

Force Variation

Force variation refers to a radial or lateral movement of the tire and wheel assembly which acts much like runout, however, force variation has to do with variations in the construction of the tire. These variations in tire construction may actually cause vibration in a vehicle, even though the tire and wheel assembly runout and balance may be within specifications.

Scheme 38

Radial force variation refers to the difference in the stiffness of a tire sidewall as the tire rotates and contacts the road. Tire sidewalls have some stiffness due to splices in the different plies of the tire, but these stiffness differences do not cause a problem unless the force variation is excessive. Stiff spots (1) in a tire sidewall can deflect a tire and wheel assembly upward as the assembly contacts the road.

Scheme 39

Lateral force variation refers to the difference in the stiffness or conformity of the belts within a tire as the tire rotates and contacts the road. Tire belts may have some stiffness or conformity differences, but these differences do not cause a problem unless the force variation is excessive. These variations in the belts of the tire can deflect the vehicle sideways or laterally. A shifted belt inside a tire may cause lateral force variation.

In most cases where excessive lateral force variation exists, the vehicle will display a wobble or waddle at low speeds - 8-40 km/h (5-25 mph) - on a smooth road surface.

Isolation Test Procedure

Perform the following test in order to determine if force variation is present in the vehicle.

1. Substitute a set of KNOWN GOOD - pre-tested - tire and wheel assemblies of the same size and type for the suspected original assemblies. Refer to Tire and Wheel Removal and Installation in Tires and Wheels.
2. Road test the vehicle to determine if the vibration is still present. Refer to Vibration Analysis - Road Testing.
3. If the vibration is still present while using the known good set of tire and wheel assemblies, then force variation is not the cause of the vibration.
4. If the vibration is eliminated when using the known good set of tire and wheel assemblies, install one of the original tire and wheel assemblies using the matchmarks made prior to removal. Refer to Tire and Wheel Removal and Installation in Tires and Wheels. Road test the vehicle to determine if the vibration has returned. Refer to Vibration Analysis - Road Testing.
5. Continue the process of installing the original tire and wheel assemblies one at a time, then road testing the vehicle, until the tire and wheel assembly, or assemblies which is causing the vibration has been identified.
6. Replace the tire, or tires on the vibration-causing tire and wheel assembly, or assemblies, then balance the assembly, or assemblies. Refer to Tire and Wheel Assembly Balancing - Off-Vehicle.

Vibration in Service-Stall Test (Non-Torque Sensitive)

Note. Do not fill the propeller shaft with foam, oil, or any other substance in order to correct a vibration. Filling the propeller shaft is only effective in reducing an unrelated condition called Torsional Rattle. Filling the propeller shaft should only be done in strict adherence to the procedure outlined in corporate bulletins that address Torsional Rattle. Failure to follow the correct procedure will induce a vibration and/or affect the structural integrity of the propeller shaft. The propeller shaft will then have to be replaced.

1. Support the vehicle on a hoist or jackstand. Support the axle(s) at curb height. Refer to Lifting and Jacking the Vehicle in General Information.
2. Turn the ignition ON.
3. Place the transmission in NEUTRAL.
4. Remove the rear tire/wheel assemblies. Refer to Tire and Wheel Removal and Installation in Tires and Wheels.
5. Remove the brake rotors. Refer to Brake Rotor Replacement - Front or Brake Rotor Replacement - Rear in Disc Brakes.
6. Inspect the propeller shaft. The propeller shaft should be free of undercoating before continuing. NOTE: Do not depress the brake pedal with the brake rotors and/or the brake drums removed, or with the brake calipers repositioned away from the brake rotors, or damage to the brake system may result.
7. Start the engine.
8. Place the transmission in the highest forward gear.
9. Have an assistant accelerate and decelerate the vehicle through the speed range at which the vibration was first noted during the Vibration Analysis-Road Testing procedure.
10. Record whether the vibration was present, and at what speed.
11. If the vibration is present, determine which end of the driveshaft is vibrating the most. Hold an J 38792-A vibration sensor up to the pinion nose and the transmission tailshaft housing.
12. If the vehicle is equipped with a multiple-piece propeller shaft, hold an J 38792-A vibration sensor up to the center support bearing(s) to inspect for vibration.
13. If the transmission tailshaft housing is vibrating, hold the J 38792-A vibration sensor up to the transmission crossmember under the transmission mount. If there is no vibration on the crossmember, then the transmission mount is working properly.
14. Record which end of the driveshaft is vibrating the most, and how severe the vibration is. The inspection will be a reference by which to judge future progress.

Vibration in Service-Stall Test (Torque Sensitive)

Note. Do not fill the propeller shaft with foam, oil, or any other substance in order to correct a vibration. Filling the propeller shaft is only effective in reducing an unrelated condition called Torsional Rattle. Filling the propeller shaft should only be done in strict adherence to the procedure outlined in corporate bulletins that address Torsional Rattle. Failure to follow the correct procedure will induce a vibration and/or affect the structural integrity of the propeller shaft. The propeller shaft will then have to be replaced.

1. Support the vehicle on a hoist or jackstand. Support the axle(s) at curb height. Refer to Lifting and Jacking the Vehicle in General Information.
2. Turn the ignition ON.
3. Place the transmission in NEUTRAL.
4. Remove the rear tire/wheel assemblies. Refer to Tire and Wheel Removal and Installation in Tires and Wheels.
5. Remove the brake rotors. Refer to Brake Rotor Replacement - Front or Brake Rotor Replacement - Rear in Disc Brakes.
6. Hold the J 38792-A sensor against the pinion nose. NOTE: Do not depress the brake pedal with the brake rotors and/or the brake drums removed, or with the brake calipers repositioned away from the brake rotors, or damage to the brake system may result.
7. Start the vehicle.
8. Place the transmission in the highest forward gear.
9. Have an assistant accelerate and decelerate the vehicle through the speed range at which the vibration was first noted during the Vibration Analysis - Road Testing procedure.
10. If a vibration is present, note the J 38792-A reading during acceleration or deceleration.
11. Note as to whether or not the pinion nose vibrates under load during the acceleration or deceleration.
12. If the vibration is not reproduced, reinstall the brake rotors and the wheel/tire assemblies to put an additional load on the system. Check the components again while an assistant maintains the vehicle at the vibration concern speed.
13. If the vibration is still not reproduced, lightly apply the brakes to further load the system while maintaining the vibration concern speed.
14. If the pinion nose vibrates under acceleration or deceleration, and other driveline components have been eliminated as a cause, the vibration may be an internal axle problem.

Scheme 40

1. J 7872 Magnetic Base Dial Indicator Set, or equivalent
2. J 8001 Dial Indicator Set, or equivalent

Scheme 41

Scheme 42

1. Raise and suitably support the vehicle. Ensure that the drive axle is supported at ride height (vehicle body supported by suspension components) with the wheels free to rotate. Refer to Lifting and Jacking the Vehicle in General Information.
2. Place the transmission in NEUTRAL.
3. Clean the circumference of the propeller shaft of any debris and/or undercoating along the front (1), center (2), and rear (3) positions.
4. Inspect the propeller shaft for dents, damage, and/or missing weights. Any propeller shaft that is dented or damaged requires replacement.
5. Mount the J 7872, or equivalent, or the J 8001, or equivalent, to the vehicle underbody, or to a service stand in order to measure the runout of the propeller shaft beginning at the rear-most position.
6. Rotate the pinion flange or the transmission yoke by hand while taking runout measurements of the propeller shaft. The propeller shaft will rotate more easily in one direction than in the other. If necessary, the tire and wheel assemblies and even the rotors/drums can be removed from the drive axle to provide easier rotation of the propeller shaft. Important: Do not include fluctuations on the dial indicator due to welds or surface irregularities.
7. Beginning at the rear-most position and working forward, record the runout measurement at the rear (3), the center (2), and the front (1) of the propeller shaft.
8. Compare the propeller shaft runout measurements recorded to the runout tolerance specifications.
9. If any of the propeller shaft runout measurements exceed the runout tolerances, perform the following: Mark the position of the propeller shaft to the pinion flange. Remove the propeller shaft from the pinion flange. Rotate the propeller shaft 180 degrees from it's original position. Reinstall the propeller shaft to the pinion flange. Remeasure and record the runout of the propeller shaft at the same 3 places measured previously. Compare the propeller shaft runout remeasurements recorded to the runout tolerance specifications. If any of the propeller shaft runout remeasurements still exceed the runout tolerances, perform the following: Inspect the pinion flange runout to determine if the pinion flange is affecting the runout of the propeller shaft. Refer to Pinion Flange Runout Measurement. If the pinion flange runout exceeds the runout tolerances, the pinion flange must be reindexed or replaced to bring the runout within tolerances before proceeding. If the pinion flange was reindexed or replaced, return the propeller shaft to it's original relationship when reinstalling the shaft to the flange. If the pinion flange runout is within tolerances, inspect the deflection of transmission output shaft for indications of a worn or damaged bushing which could be affecting the runout of the propeller shaft. A leaking transmission output shaft seal may be an indication of an output shaft bushing concern. If the transmission output shaft bushing is found to be worn or damaged, the bushing must be replaced before proceeding. Important: Inspect the runout of any replacement propeller shaft. If the first measurement of pinion flange runout was within tolerances and the transmission output shaft bushing was not found to be worn or damaged, the propeller shaft requires replacement. Check the runout of the replacement propeller shaft. If either the pinion flange was reindexed or replaced, or if the transmission output shaft bushing was replaced; remeasure and record the runout of the propeller shaft at the same 3 places measured previously. Compare the propeller shaft runout remeasurements recorded to the runout tolerance specifications. If any of the propeller shaft runout remeasurements still exceed the runout tolerances, remove and rotate the propeller shaft 180 degrees from it's original position at the reindexed or replaced pinion flange. Reinstall the propeller shaft to the reindexed or replaced pinion flange then remeasure and record the runout of the propeller shaft at the same 3 places measured previously. Compare the propeller shaft runout remeasurements recorded to the runout tolerance specifications. Important: Inspect the runout of any replacement propeller shaft. If any of the propeller shaft runout remeasurements still exceed the runout tolerances, the propeller shaft requires replacement. Check the runout of the replacement propeller shaft.

Scheme 43

1. J 8001 Dial Indicator Set, or equivalent
2. J 23409 Dial Indicator Extension, or equivalent
3. J 35819 Flange Runout Gage

System balanced drive axles utilize a deflector design on the pinion flange, that is able to hold system balance weights on its outside diameter.

Scheme 44

1. Raise and support the vehicle, with the wheels free to rotate. Refer to Lifting and Jacking the Vehicle in General information.
2. Remove the propeller shaft from the pinion flange.
3. Install the J 35819 to the pinion flange.
4. Assemble and install the J 8001 and the J 23409 to the drive axle and to the J 35819. Important: The dial indicator will display inverted readings. You are measuring the inside diameter of the flange, not the outside diameter. The highest reading on the dial indicator is the low spot; the lowest reading is the high spot.
5. Rotate the pinion flange 360 degrees and zero the dial indicator on the low spot.
6. Rotate the pinion flange again and record the total runout. Important: All runout measurement tolerances provided are to be used as guidelines. The measurement tolerances provided and their effect on vibration correction may vary for each vehicle.
7. If the system balanced pinion flange runout measurement is between 0.00-0.38 mm (0.00-0.015 in), the pinion flange is considered within acceptable runout limits.
8. If the system balanced pinion flange runout measurement exceeds 0.00-0.38 mm (0.00-0.015 in), the pinion flange must be reindexed 180 degrees or replaced. If the drive axle utilizes a crush-type sleeve to achieve pinion bearing preload, the pinion flange can only be removed and installed 1 time before the crush-type sleeve must be replaced. Sleeve replacement requires removal and installation of the ring and pinion gear set. If there is evidence that the pinion has been removed and installed previously, replace the sleeve.
9. If the pinion flange has been reindexed, remeasure the pinion flange runout.
10. If the runout remeasurement of the reindexed pinion flange still exceeds the tolerance guidelines, the pinion flange requires replacement. Important: Inspect the runout of any replacement pinion flange.
11. If the pinion flange was replaced, check the runout of the replacement pinion flange. Important: If the pinion flange was reindexed or replaced, the driveline MUST be system balanced.
12. If the pinion flange was reindexed or replaced, system balance the driveline. Refer to Driveline System Balance Adjustment.

Scheme 45

1. J 8001 Dial Indicator Set, or equivalent
2. J 23409 Dial Indicator Extension, or equivalent
3. J 35819 Flange Runout Gage

Drive axles that are non-system balanced use a pinion flange dust slinger design, that is able to hold a runout compensation weight on the face of the dust slinger.

Scheme 46

1. Raise and support the vehicle, with the wheels free to rotate. Refer to Lifting and Jacking the Vehicle in General information.
2. Remove the propeller shaft from the pinion flange.
3. Install the J 35819 to the pinion flange.
4. Assemble and install the J 8001 and the J 23409 to the drive axle and to the J 35819. Important: The dial indicator will display inverted readings. You are measuring the inside diameter of the flange, not the outside diameter. The highest reading on the dial indicator is the low spot; the lowest reading is the high spot.
5. Rotate the pinion flange 360 degrees and zero the dial indicator on the low spot.
6. Rotate the pinion flange again and record the total runout. Important: All runout measurement tolerances provided are to be used as guidelines. The measurement tolerances provided and their effect on vibration correction may vary for each vehicle.
7. If the pinion flange runout is 0.15 mm (0.006 in) or less, there should not be a runout compensation weight. If there is a compensation weight, remove the weight.
8. If the pinion flange runout is greater than 0.15 mm (0.006 in) but less than 0.28 mm (0.011 in) and the runout compensation weight is at or near the low spot, no further action is necessary. If the runout compensation weight is not at or near the low spot, remove the weight.
9. If the pinion flange runout is greater than 0.28 mm (0.011 in) but not greater than 0.38 mm (0.015 in) and the runout compensation weight is at or near the low spot, no further action is necessary. If the runout compensation weight is not at or near the low spot, remove the weight and re-index the pinion flange until the runout is 0.25 mm (0.010 in) or less. If the drive axle utilizes a crush-type sleeve to achieve pinion bearing preload, the pinion flange can only be removed and installed 1 time before the crush-type sleeve must be replaced. Sleeve replacement requires removal and installation of the ring and pinion gear set. If there is evidence that the pinion has been removed and installed previously, replace the sleeve.
10. If after reindexing the pinion flange, it is not possible to achieve runout of 0.25 mm (0.010 in) or less, the pinion flange requires replacement. Important: Inspect the runout of any replacement pinion flange.
11. If the pinion flange was replaced, check the runout of the replacement pinion flange.

Scheme 47

1. J 23498-A Driveshaft Inclinometer
2. J 23498-20 Driveshaft Inclinometer Adapter

The working angle of a U-joint is formed by the difference between the angles of two shafts that intersect. One-piece propeller shaft systems have two working angles; front (1) and rear (2).

1. The front working angle (1) is formed by the intersection of the transmission output shaft and the propeller shaft.
2. The rear working angle (2) is formed by the intersection of the propeller shaft and the drive axle pinion.

Two-piece systems contain three working angles.

When measuring and evaluating driveline working angles, observe the following

Scheme 48

1. The two working, or cancelling angles should be equal to each other within 1/2 degree to provide effective cancellation of the U-joints.
2. Two-piece systems contain an odd, or non-cancelled angle - the front angle - that should be between 1/10 and 1/2 degree.
3. No working angle should exceed 4 degrees.
4. No working angle should be equal to zero. An angle of 0 degrees will cause premature U-joint wear due to a lack of rotation of the needle bearings in the U-joint.
5. Always orientate the J 23498-A so that it faces the same side of the vehicle for each measurement taken.
6. Be sure to accurately record the measurements taken on a diagram, similar to the one shown.

Measurement Procedure

Important: If it is necessary to use the J 23498-20 adapter, first verify the accuracy of the J 23498-20 by inspecting the angle of an accessible joint using the J 23498-A, then inspecting the same joint angle using the J 23498-20.

Scheme 49

Scheme 50

Scheme 51

Scheme 52

1. Raise and support the vehicle. Ensure that the drive axle is supported at ride height - vehicle body supported by suspension components - with the wheels free to rotate. Refer to Lifting and Jacking the Vehicle in General Information.
2. For two-piece propeller shaft systems, inspect the lateral alignment of the propeller shafts before proceeding. From underneath the propeller shafts, look down the length of the shafts from front to rear. Inspect the alignment of the shafts to each other. From underneath the shafts, if the propeller shafts are not aligned to each other in a straight line, then the lateral alignment of the propeller shafts needs to be adjusted before proceeding. The propeller shaft support bearing assembly can be relocated slightly to one side in order to improve the alignment of the shafts. Ensure that you do not create a ground-out condition against the exhaust or any other component.
3. Place the transmission in NEUTRAL.
4. Ensure that the vehicle has a full tank of fuel or the equivalent amount of weight in the rear to simulate a full tank. The weight of 3.8 L (1 gal) of gasoline is approximately 2.8 kg (6.2 lb).
5. Clean any corrosion or foreign material from the U-joint bearing caps.
6. Remove any of the U-joint bearing cap snap rings that may interfere with the correct placement of the J 23498-A.
7. Measure the angle of the drive axle pinion. Rotate the drive axle pinion to align the pinion yoke flanges vertically. Install the J 23498-A to the lower U-joint bearing cap of the drive axle pinion. Using the J 23498-A, measure and record the angle of the drive axle pinion.
8. For one-piece systems, measure the angle of the transmission output shaft yoke. Do not rotate the propeller shaft. With the propeller shaft in the same position, the transmission output shaft yoke flange will be aligned vertically. Install the J 23498-A to the lower U-joint bearing cap of the transmission output shaft yoke. Using the J 23498-A, measure and record the angle of the transmission output shaft yoke - one-piece system.
9. For two-piece systems, measure the angle of the front propeller shaft. Do not rotate the propeller shafts. With the propeller shafts in the same position, the U-joints of the front propeller shaft will be aligned vertically. Install the J 23498-A to the lower U-joint bearing cap of either of the U-joints on the front propeller shaft. Using the J 23498-A, measure and record the angle of the front propeller shaft - two-piece system.
10. Rotate the propeller shaft, or shafts 1/4 turn.
11. For one-piece systems, measure the angle of the front propeller shaft. Do not rotate the propeller shaft. With the propeller shaft in this position, the U-joints of the front propeller shaft will be aligned vertically. Install the J 23498-A to the lower U-joint bearing cap of either of the U-joints on the front propeller shaft. Using the J 23498-A, measure and record the angle of the front propeller shaft - one-piece system.
12. For two-piece systems, measure the angle of the transmission output shaft yoke. Do not rotate the propeller shafts. With the propeller shafts in this position, the transmission output shaft yoke flanges will be aligned vertically. Install the J 23498-A to the lower U-joint bearing cap of the transmission output shaft yoke. Using the J 23498-A, measure and record the angle of the transmission output shaft yoke - two-piece system.
13. Remove the J 23498-A.
14. Install any U-joint bearing cap snap rings that were removed prior to installing the J 23498-A.
15. Calculate the working angles at each intersection of two shafts. Subtract the larger number from the smaller to obtain the working angle. For example: If the drive axle pinion has an angle of 16 degrees and the connecting propeller shaft has an angle of 13 degrees, then the working angle of that intersection is 3 degrees.
16. Compare the working angles of cancelling U-joints, beginning at the rear-most position.
17. If the working angles of two cancelling U-joints are not within 1/2 degree of each other, or if one or both of the angles exceed 4 degrees, then the angle requires adjustment.
18. For two-piece systems, if the working angle of the non-cancelling, front U-joint is not between 1/10-1/2 degree, then the angle requires adjustment.

J 23498-A Driveshaft Inclinometer

Inspect the propeller shaft for correct phasing. Correct phasing means that the front and the rear U-joint are directly in line or parallel with each other so that proper cancellation takes place.

Scheme 53

1. Raise and support the vehicle. Ensure that the drive axle is supported at ride height - vehicle body supported by suspension components - with the wheels free to rotate. Refer to Lifting and Jacking the Vehicle in General Information.
2. Place the transmission in NEUTRAL.
3. Clean any corrosion or foreign material from the U-joint bearing caps.
4. Remove any of the U-joint bearing cap snap rings that may interfere with the correct placement of the J 23498-A.
5. Inspect the propeller shaft - one-piece system, or the rear propeller shaft - two-piece system, for proper phasing. Rotate the propeller shaft, or shafts to align the rear shaft flanges vertically. Install the J 23498-A to the lower U-joint bearing cap of the rear U-joint of the - rear - propeller shaft. The J 23498-A should be aligned perpendicular to the propeller shaft. Set the indicator line on the J 23498-A to 15, the horizontal reference. Rotate the propeller shaft slightly to center the bubble to the indicator. The U-joint is now vertical. Without disturbing the setting on the J 23498-A, remove the J 23498-A from the rear U-joint bearing cap. Install the J 23498-A to the lower U-joint bearing cap of the front U-joint of the - rear - propeller shaft. Observe the reading of the front U-joint with the J 23498-A still set to 15, the horizontal reference.
6. If the difference between the front and rear U-joints of a welded-yoke propeller shaft is 3 degrees or less, the propeller shaft is properly phased.
7. If the difference between the front and rear U-joints of a welded-yoke propeller shaft is greater than 3 degrees, the propeller shaft is either constructed improperly, or damaged from twisting and it requires replacement to restore proper cancellation of the U-joints.
8. Inspect the front propeller shaft-to-slip yoke - two-piece system - for proper phasing. Rotate the propeller shafts to align the front shaft and the slip yoke flanges vertically. Install the J 23498-A to the lower U-joint bearing cap of the slip yoke. The J 23498-A should be aligned perpendicular to the propeller shaft. Set the indicator line on the J 23498-A to 15, the horizontal reference. Rotate the propeller shaft slightly to center the bubble to the indicator. The U-joint is now vertical. Without disturbing the setting on the J 23498-A, remove the J 23498-A from the slip yoke U-joint bearing cap. Install the J 23498-A to the lower U-joint bearing cap of the front U-joint of the front propeller shaft - two-piece system. Observe the reading of the front U-joint with the J 23498-A still set to 15, the horizontal reference.
9. If the difference between the front propeller shaft U-joint and the slip yoke U-joint - two-piece system - is 3 degrees or less, the propeller shaft and the slip yoke are properly phased to each other.
10. If the difference between the front propeller shaft U-joint and the slip yoke U-joint - two-piece system - is greater than 3 degrees, the propeller shaft and the slip yoke are not aligned properly to each other at the stub shaft, constructed improperly, or damaged from twisting. If the stub shaft is keyed to ensure properly alignment of the front shaft and the slip yoke, then the propeller shafts require replacement to restore proper cancellation of the U-joints. If the stub shaft is not keyed, attempt to re-align the front shaft and slip yoke to each other. Repeat this inspection procedure to confirm the results. If proper phasing cannot be obtained, then the propeller shafts require replacement to restore proper cancellation of the U-joints.

Tire and Wheel Assembly Balancing - Off-Vehicle

1. Clean away any dirt or deposits from the inside of the wheels.
2. Remove any stones from the tread.
3. Wear eye protection.
4. Use coated weights on aluminum wheels.

Tire and Wheel Assembly Balancer Calibration

Tire and wheel balancers can drift out of calibration over time, or can become inaccurate as a result of heavy use. There will likely not be any visual evidence that a calibration problem exists. If a balancer is not calibrated within specifications, and a tire and wheel assembly is balanced on that machine, the assembly may actually be imbalance.

Tire and wheel assembly balancer calibration should be checked approximately every 2 weeks, if the machine is used frequently, and/or whenever the balance readings are questionable.

Tire and Wheel Assembly Balancer Calibration Test

Important: If the balancer fails any of the steps in this calibration test, the balancer should be calibrated according to the manufacturer's instructions. If the balancer cannot be calibrated, contact the manufacturer for assistance.

Check the calibration of the tire and wheel assembly balancer according to the manufacturer's recommendations, or perform the following test.

Scheme 54

1. Spin the balancer without a wheel or any of the adapters on the shaft.
2. Inspect the balancer readings. Specification Zero within 7 g (1/4 oz)
3. If the balancer is within the specification range, balance a tire and wheel assembly - that is within radial and lateral runout tolerances - to ZERO, using the same balancer.
4. After the tire and wheel assembly has been balanced, add an 85 g (3 oz) test weight to the wheel at any location.
5. Spin the tire and wheel assembly again. Note the readings. In the static and dynamic modes, the balancer should call for 85 g (3 oz) of weight, 180 degrees opposite the test weight. In the dynamic mode, the weight should be called for on the flange of the wheel opposite the test weight.
6. With the assembly imbalance to 85 g (3 oz), cycle the balancer 5 times.
7. Inspect the balancer readings: Specification Maximum variation: 7 g (1/4 oz)
8. Index the tire and wheel assembly on the balancer shaft, 90 degrees from the previous location.
9. Cycle the balancer with the assembly at the new location.
10. Inspect the balancer readings: Specification Maximum variation: 7 g (1/4 oz)
11. Repeat steps 8 through 10 until the tire and wheel assembly has been cycled and checked at each of the 4 locations on the balancer shaft.

Tire and Wheel Assembly Balancing Guidelines

Important: Tire and wheel assemblies which exhibit excessive runout can produce vibrations even if the assemblies are balanced. It is strongly recommended that the tire and wheel assembly runout be measured and corrected if necessary BEFORE the assemblies are balanced.

If the runout of the tire and wheel assemblies has not yet been measured, refer to Tire and Wheel Assembly Runout Measurement - Off-Vehicle before proceeding.

There are 2 types of tire and wheel balance

Scheme 55

Static balance is the equal distribution of weight around the wheel circumference. The wheel balance weights (2) are positioned on the wheel in order to offset the effects of a heavy spot (3). Wheels that have static imbalance can produce a bouncing action called tramp.

Scheme 56

Dynamic balance is the equal distribution of weight on each side of the tire and wheel assembly centerline. The wheel balance weights (2) are positioned on the wheel in order to offset the effects of a heavy spot (3). Wheels that have dynamic imbalance have a tendency to move from side to side and can cause an action called shimmy.

Most off-vehicle balancers are capable of checking both types of balance simultaneously.

As a general rule, most vehicles are more sensitive to static imbalance than to dynamic imbalance; however, vehicles equipped with low profile, wide tread path, high performance tires and wheels are susceptible to small amounts of dynamic imbalance. As little as 14-21 g (1/2-3/4 oz) imbalance is capable of inducing a vibration in some vehicle models.

Balancing Procedure

Important: When balancing tire and wheel assemblies, use a known good, recently calibrated, off-vehicle, two-plane dynamic balancer set to the finest balance mode available.

1. Raise and support the vehicle. Refer to Lifting and Jacking the Vehicle in General Information.
2. Mark the location of the wheels to the wheel studs and mark the specific vehicle position on each tire and wheel - LF, LR, RF, RR.
3. Remove the tire and wheel assemblies one at a time and mount on a spin-type wheel balancer. Refer to Tire and Wheel Removal and Installation in Tires and Wheels.
4. Carefully follow the wheel balancer manufacturer's instructions for proper mounting techniques to be used on different types of wheels. Regard aftermarket wheels, especially those incorporating universal lug patterns, as potential sources of runout and mounting concerns.
5. Be sure to use the correct type of wheel balance weights for the type of wheel rim being balanced. Be sure to use the correct type of coated wheel balance weights on aluminum wheels. Refer to Wheel Weight Usage.
6. Balance all four tire and wheel assemblies as close to zero as possible.
7. Using the matchmarks made prior to removal, install the tire and wheel assemblies to the vehicle. Refer to Tire and Wheel Removal and Installation in Tires and Wheels.
8. Lower the vehicle.

Wheel Weight Usage

Tire and wheel assemblies can be balanced using either the static or dynamic method.

Scheme 57

Important: When balancing factory aluminum wheels with clip-on wheel balance weights, be sure to use special polyester-coated weights. These coated weights reduce the potential for corrosion and damage to aluminum wheels.

These coated weights reduce the potential for corrosion and damage to aluminum wheels.

1. MC (1) and AW (2) series weights are approved for use on aluminum wheels.
2. P (3) series weights are approved for use on steel wheels only.
3. T (4) series coated weights are approved for use on both steel and aluminum wheels.

Scheme 58

Important: Use a nylon or plastic-tipped hammer when installing coated clip-on wheel balance weights to minimize the possibility of damage to the polyester coating.

The contour and style of the wheel rim flange will determine which type of clip-on wheel weight (1) should be used. The weight should follow the contour of the rim flange. The weight clip should firmly grip the rim flange.

Scheme 59

When static balancing, locate the wheel balance weights on the inboard flange (2) if only 28 g (1 oz) or less is called for. If more than 28 g (1 oz) is called for, split the weights as equally as possible between the inboard (2) and outboard (1) flanges.

When dynamic balancing, locate the wheel balance weights on the inboard (2) and outboard (1) rim flanges at the positions specified by the wheel balancer.

Scheme 60

Important: When installing adhesive balance weights on flangeless wheels, do NOT install the weight on the outboard surface of the rim.

Adhesive wheel balance weights may be used on factory aluminum wheels. Perform the following procedure to install adhesive wheel balance weights.

1. Determine the correct areas for placement of the wheel weights on the wheel. When static balancing, locate the wheel balance weights along the wheel centerline (1) on the inner wheel surface if only 28 g (1 oz) or less is called for. If more than 28 g (1 oz) is called for, split the weights as equally as possible between the wheel centerline and the inboard edge of the inner wheel surface (2). When dynamic balancing, locate the wheel balance weights along the wheel centerline and the inboard edge of the inner wheel surface (2) at the positions specified by the wheel balancer.
2. Ensure that there is sufficient clearance between the wheel weights and brake system components. Important: Do not use abrasives to clean any surface of the wheel.
3. Using a clean cloth or paper towel with a general purpose cleaner, thoroughly clean the designated balance weight attachment areas of any corrosion, overspray, dirt or any other foreign material.
4. To ensure there is no remaining residue, wipe the balance weight attachment areas again, using a clean cloth or paper towel with a mixture of half isopropyl alcohol and half water.
5. Dry the attachment areas with hot air until the wheel surface is warm to the touch.
6. Warm the adhesive backing on the wheel balance weights to room temperature.
7. Remove the protective covering from the adhesive backing on the back of the balance weights. DO NOT touch the adhesive surface.
8. Apply the wheel balance weights to the wheel, press into place with hand pressure.
9. Secure the wheel balance weights to the wheel with a 90 N (21 lb) force applied with a roller.

J 38792-A Electronic Vibration Analyzer (EVA) 2

If after following the tire and wheel vibration diagnostic process, some amount of tire and wheel vibration is still evident, an on-vehicle high-speed spin balancer may be used to perform an on-vehicle balance in an attempt to finish balance the tire and wheel assemblies, wheel hubs, brake rotors, brake drums, if equipped, and wheel trim, if equipped, simultaneously. On-vehicle balancing can also compensate for minor amounts of residual runout encountered as a result of mounting the tire and wheel assembly on the vehicle, as opposed to the balance which was achieved on the off-vehicle balancer.

In order to perform an on-vehicle balancing procedure, carefully follow the on-vehicle balancer manufacturer's specific operating instructions and carefully consider the following information before proceeding

1. Vehicles equipped with low profile, wide tread path, high performance tires and wheels are susceptible to small amounts of dynamic imbalance.
2. When performing an on-vehicle balance, great care must be taken when placing the wheel balance weights on the wheels. If the wheel balance weights are not placed accurately, they can actually induce dynamic imbalance and thus increase the severity of the vibration.
3. Inspect the vehicle wheel bearings to ensure that they are in good condition.
4. Thoroughly inspect all on-vehicle balancing equipment and ensure that it is fully within the manufacturer's recommended specifications.
5. Do not remove the off-vehicle balance weights. The purpose of on-vehicle balance is to fine tune the assembly balance already achieved off-vehicle, not to start over.
6. Leave all wheel trim installed whenever possible.
7. If the on-vehicle balancer calls for more than 56 g (2 oz) of additional weight, split the weight between the inboard and outboard flanges of the wheel, so as not to upset the dynamic balance of the assembly achieved in the off-vehicle balance. For wheel balance weight information, refer to Tire and Wheel Assembly Balancing - Off-Vehicle.
8. If available, tape-off an area on top of the fenders and the quarter panels, then place the vibration sensor of the J 38792-A on the fender or quarter panel above the specific tire and wheel assembly while it is being on-vehicle balanced. The J 38792-A will provide a visual indication of the amplitude of the vibration, and the effect that the on-vehicle balance has on it.

Scheme 61

Important: After remounting a tire to a wheel or after replacing a tire and/or a wheel, remeasure the tire and wheel assembly runout in order to verify that the amount of runout has been reduced and brought to within tolerances. Ensure that the tire and wheel assembly is properly balanced before reinstalling to the vehicle.

Scheme 62

1. Mark the location of the high spot (3) on the tire as determined during the off-vehicle tire and wheel assembly runout measurement.
2. Place a reference mark (2) on the tire sidewall at the location of the valve stem (5). Always refer to the valve stem as the 12 o'clock position. Refer to the location of the high spot (3) by its clock position on the wheel, relative to the valve stem.
3. Mount the tire and wheel assembly on a tire machine and break down the bead. Do not dismount the tire from the wheel at this time.
4. Rotate the tire 180 degrees on the rim so that the valve stem reference mark (8) is now at the 6 o'clock position in relation to the valve stem (6). You may need to lubricate the bead in order to easily rotate the tire on the wheel.
5. Reinflate the tire and seat the bead properly.
6. Mount the assembly on the tire balancer and remeasure the runout. Mark the new location of the assembly runout high spot on the tire.
7. If the assembly runout has been reduced and is within tolerance, no further steps are necessary. Balance the tire and wheel assembly, then install the assembly to the vehicle. Refer to the following: Tire and Wheel Assembly Balancing - Off-Vehicle Tire and Wheel Removal and Installation in Tires and Wheels
8. If the clock location of the high spot remained at or near the original clock location of the high spot (7) and the assembly run out has NOT been reduced, the wheel is the major contributor to the assembly runout concern.
9. If the clock location of the high spot has moved, however the assembly runout has NOT been reduced, perform the following steps: If the clock location of the high spot (7) is now at or near a position 180 degrees from the original clock location of the high spot, the tire is the major contributor to the assembly runout concern. If the clock location of the high spot is now in-between the 2 extremes, then both the tire and the wheel are both contributing to the assembly runout concern. Rotate the tire an additional 90 degrees in both the clockwise and the counterclockwise directions to obtain the lowest amount of assembly runout.

Tire and Wheel Assembly-to-Hub/Axle Flange Match-Mounting

Important: After remounting a tire and wheel assembly to a hub/axle flange, remeasure the tire and wheel assembly on-vehicle runout in order to verify that the amount of runout has been reduced and brought to within tolerances.

1. Mark the location of the high spot on the tire and wheel assembly as determined during the on-vehicle tire and wheel assembly runout measurement.
2. Place a reference mark on the wheel stud that is located closest to the wheel valve stem. Always refer to the reference mark on the wheel stud as the 12 o'clock position. Refer to the location of the high spot by its clock position on the tire and wheel assembly, relative to the marked wheel stud.
3. Remove the tire and wheel assembly from the hub/axle flange. Refer to Tire and Wheel Removal and Installation in Tires and Wheels.
4. Rotate the tire and wheel assembly as close to 180 degrees as possible on the hub/axle flange, so that the wheel valve stem is now approximately at the 6 o'clock position in relation to the marked wheel stud.
5. Reinstall the wheel lug nuts to secure the tire and wheel assembly in the new position. Refer to Tire and Wheel Removal and Installation in Tires and Wheels.
6. Remeasure the tire and wheel assembly on-vehicle runout. Mark the new location of the assembly on-vehicle runout high spot on the tire. Refer to Tire and Wheel Assembly Runout Measurement - On-Vehicle.
7. If the assembly on-vehicle runout has been reduced and is within tolerance, no further steps are necessary.
8. If the assembly runout has NOT been reduced, perform the following steps: If the clock location of the high spot remained at or near the original clock location of the high spot, the hub/axle flange and/or the brake rotor/drum mounting flange is the major contributor to the assembly on-vehicle runout concern. If the clock location of the high spot is now at or near a position 180 degrees from the original clock location of the high spot, the tire and wheel assembly is the major contributor to the assembly on-vehicle runout concern. If the clock location of the high spot is now in-between the two extremes, then both the tire and wheel assembly and the hub/axle flange are contributing to the assembly on-vehicle runout concern. Rotate the tire and wheel assembly as close to an additional 90 degrees as possible in both the clockwise and the counterclockwise directions to obtain the lowest amount of assembly on-vehicle runout.

Driveline System Balance Adjustment (Using EVA)

This procedure is designed to fine-tune the balance of a propeller shaft while it is mounted in the vehicle. Small amounts of residual imbalance which could be present in other related driveline system components could be compensated for as a result of performing this procedure. The end result of properly fine-tuning a propeller shaft balance may be either a significant reduction or an elimination of a vibration disturbance that is related to the first-order rotation of a propeller shaft.

Fine-tuning the balance of a propeller shaft can aid in achieving a more balanced total driveline system.

Important: The runout of the propeller shaft to be balanced and the runout of the components that the propeller shaft mates to must be within tolerances before an attempt should be made to perform this procedure.

1. J 38792-A Electronic Vibration Analyzer 2
2. J 38792-20 20-Foot Timing Light Power Cord Extension
3. J 38792-25 Inductive Pickup Timing Light, or equivalent
4. J 38792-27 6-Foot EVA Power Cord Extension

Adjustment Procedure

Note. Do not depress the brake pedal with the brake rotors and/or the brake drums removed, or with the brake calipers repositioned away from the brake rotors, or damage to the brake system may result.

Scheme 63

Scheme 64

1. Raise and support the vehicle; ensure that the drive axle(s) are supported at ride height - vehicle body supported by suspension components. Refer to Lifting and Jacking the Vehicle in General Information.
2. With the tire and wheel assemblies, and the brake rotors and/or brake drums removed from the drive axle, or axles, start the engine and turn OFF all engine accessories.
3. Place the transmission in forward gear.
4. Run the vehicle at the speed which causes the most vibration in the propeller shaft; observe which end of the propeller shaft exhibits the greatest amount of vibration disturbance.
5. Turn the engine OFF to slow and stop the rotation of the propeller shaft.
6. Mark the circumference of the propeller shaft (1) to be balanced at four points 90 degrees apart (2), nearest the end that exhibited the greatest amount of vibration. Number the marks 1 through 4.
7. Install the J 38792-A, the J 38792-27, the J 38792-25, or equivalent, and the J 38792-20 to the vehicle.
8. Connect the clip of the J 38792-25, or equivalent, onto the trigger wire of the J 38792-A.
9. Mount the J 38792-A vibration sensor to the bottom of the driveline component nearest to the end of the propeller shaft that exhibited the greatest amount of vibration. Ensure that the side of the sensor marked UP faces upward and that the sensor is positioned as close to horizontal as possible.
10. Plug the vibration sensor cord into Input A of the J 38792-A. Input B is not used with the strobe function.
11. Run the vehicle at the speed which causes the most vibration in the propeller shaft; observe the frequency readings displayed on the J 38792-A. Important: Do NOT continue with fine-tuning the balance of a propeller shaft if the dominant frequency displayed is not related to the first-order rotational speed of the propeller shaft.
12. Verify that the dominant frequency displayed on the J 38792-A matches the recorded frequency of the vibration concern.
13. Record the amplitude reading of the dominant frequency displayed.
14. Using the strobe function of the J 38792-A, select the correct filter range to use for the balance adjustment, so that the dominant frequency would be near the middle of the filter range. Use the full range filter only as a last resort if one of the specific range filters will not cover the frequency adequately.
15. The J 38792-A display will show the dominant frequency, the amplitude and the selected filter range.
16. Aim the J 38792-25, or equivalent, at the marks placed on the propeller shaft. When activated, the strobe effect will appear to freeze the marks placed on the rotating propeller shaft. Record which of the numbered marks appears to be at the bottom of the propeller shaft, or the 6 o'clock position. This position identifies the light spot of the propeller shaft.
17. Turn the engine OFF to slow and stop the rotation of the propeller shaft.
18. Install a band-type hose clamp as a weight, with the head of the clamp directly on the light spot.
19. Run the vehicle at the speed which causes the most vibration in the propeller shaft.
20. Using the J 38792-25, or equivalent, observe the positioning of the marks placed on the propeller shaft.
21. If the marks on the propeller shaft now appear to move erratically, compare the current amplitude of the vibration frequency to the original amplitude recorded previously. If the amplitude has decreased from the amplitude recorded, the balance achieved may be sufficient and the vehicle should be road tested to determine the effect on the vibration concern.
22. If the clamp head over the original light spot, is now near the top of the propeller shaft, within 180 degrees - near or below the 12 o'clock position - of the original position at the bottom of the propeller shaft - 6 o'clock position - the position of the weight needs adjusting. Perform the following steps: Move the position of the clamp head toward the 6 o'clock position. Using the J 38792-25, or equivalent, recheck the positioning of the propeller shaft marks. If necessary, continue to move the position of the clamp head toward the 6 o'clock position and recheck progress until an improvement in balance is achieved.
23. If the clamp head over the original light spot, is still positioned at the bottom of the propeller shaft - 6 o'clock position - additional weight is required. Perform the following steps: Add a second clamp to the propeller shaft, next to the first clamp and with the clamp heads aligned. Using the J 38792-25, or equivalent, recheck the positioning of the propeller shaft marks. If the clamp heads over the original light spot, are now 90 to 180 degrees - at or above the 9 o'clock or the 3 o'clock positions - from the original position at the bottom of the propeller shaft - 6 o'clock position - less total weight is required. Proceed to step 23.4. Move the position of the clamp heads an equal distance on either side of the light spot between 1 and 120 degrees apart from each other to reduce the total amount of weight in relation to the lightspot. Using the J 38792-25, or equivalent, recheck the positioning of the propeller shaft marks. If necessary, continue to move the position of the clamp heads an equal distance on either side of the light spot to a maximum of 120 degrees apart from each other, until the greatest improvement to balance is achieved. If improvement has been made to the balance of the propeller shaft, but the balance is still not satisfactory, still more total weight may be required. Perform the following steps: Add a third clamp to the propeller shaft, next to the first and second clamps and with the clamp head directly on the light spot. Move the position of the first and second clamp heads an equal distance on either side of the light spot between 1 and 120 degrees apart from each other to arrive at a total amount of weight greater than two weights, but less than three weights in relation to the light spot. Using the J 38792-25, or equivalent, recheck the positioning of the propeller shaft marks. If necessary, continue to move the position of the first and second clamp heads an equal distance on either side of the light spot to a maximum of 120 degrees apart from each other, until the greatest improvement to balance is achieved. If a third clamp was used on the propeller shaft and sufficient balance could still not be achieved, the propeller shaft requires replacement.
24. If the clamp head over the original light spot is now 90 to 180 degrees - at or above the 9 o'clock or the 3 o'clock positions - from the original position at the bottom of the propeller shaft - 6 o'clock position - less total weight is required. Perform the following steps: Add a second clamp to the propeller shaft, next to the first clamp and with the clamp heads aligned. Move the position of the clamp heads an equal distance on either side of the light spot between 120 and 180 degrees apart from each other to reduce the total amount of weight in relation to the lightspot. Using the J 38792-25, or equivalent, recheck the positioning of the propeller shaft marks. If necessary, continue to move the position of the clamp heads an equal distance on either side of the light spot to a maximum of 180 degrees apart from each other, but not less than 120 degrees apart, until the greatest improvement to balance is achieved.
25. If the marks on the propeller shaft now appear to move erratically, compare the current amplitude of the vibration frequency to the original amplitude recorded previously. If the amplitude has decreased from the amplitude recorded, the balance achieved may be sufficient and the vehicle should be road tested to determine the effect on the vibration concern.

Driveline System Balance Adjustment (Without EVA)

This procedure is designed to fine-tune the balance of a propeller shaft while it is mounted in the vehicle. Small amounts of residual imbalance which could be present in other related driveline system components could be compensated for as a result of performing this procedure. The end result of properly fine-tuning a propeller shaft balance may be either a significant reduction or an elimination of a vibration disturbance that is related to the first-order rotation of a propeller shaft.

Fine-tuning the balance of a propeller shaft can aid in achieving a more balanced total driveline system.

Important: The runout of the propeller shaft to be balanced and the runout of the components that the propeller shaft mates to must be within tolerances before an attempt should be made to perform this procedure.

Note. Do not depress the brake pedal with the brake rotors and/or the brake drums removed, or with the brake calipers repositioned away from the brake rotors, or damage to the brake system may result.

1. Raise and support the vehicle; ensure that the drive axle, or axles are supported at ride height - vehicle body supported by suspension components. Refer to Lifting and Jacking the Vehicle in General Information.
2. With the tire and wheel assemblies, and the brake rotors and/or brake drums removed from the drive axle(s), start the engine and turn OFF all engine accessories.
3. Place the transmission in forward gear.
4. Run the vehicle at the speed which causes the most vibration in the propeller shaft; observe which end of the propeller shaft exhibits the greatest amount of vibration disturbance.
5. Carefully hold a piece of chalk up to the end of the propeller shaft in order to just make contact as the shaft rotates.
6. Turn the engine OFF to slow and stop the rotation of the propeller shaft.
7. Observe the location of the chalk mark on the propeller shaft. If the chalk mark circles the entire propeller shaft after the first attempt, remove the mark from the shaft and repeat steps 2 through 7 touch the chalk more gently to the propeller shaft. If the chalk mark circles the entire propeller shaft after the second attempt, runout of the propeller shaft may not be the cause of the disturbance. Proceed to step 16. If the chalk mark is only on a small portion of the propeller shaft, the mark identifies the heavy spot of the propeller shaft. The heavy spot of the propeller shaft will deflect downward during rotation. Place a small mark on the shaft 180 degrees, directly opposite the heavy spot, and identify the mark as the light spot. Proceed to step 8.
8. Install a band-type hose clamp to the propeller shaft as a weight, with the head of the clamp directly on the light spot, or 180 degrees, directly opposite the heavy spot.
9. Observe the amount of disturbance to the propeller shaft. If the amount of disturbance to the propeller shaft appears to be significantly reduced, the balance achieved may be sufficient and the vehicle should be road tested to determine the effect on the vibration concern. The head of the clamp can be moved very slightly, if necessary to refine the balance achieved. If the amount of disturbance to the propeller shaft appears to be almost unchanged or even increased, proceed to step 10.
10. Add a second clamp to the propeller shaft, next to the first clamp and with the clamp heads aligned.
11. Observe the amount of disturbance to the propeller shaft. If the amount of disturbance to the propeller shaft appears to be significantly reduced, the balance achieved may be sufficient and the vehicle should be road tested to determine the effect on the vibration concern. The head of the clamps can be moved very slightly an equal distance apart on either side of the light spot, or moved slightly while still aligned, if necessary to refine the balance achieved. If the amount of disturbance to the propeller shaft appears to be almost unchanged or even increased, proceed to step 12.
12. Move the position of the clamp heads an equal distance on either side of the light spot between 1 and 120 degrees apart from each other to reduce the total amount of weight in relation to the lightspot.
13. Observe the amount of disturbance to the propeller shaft. If the amount of disturbance to the propeller shaft appears to be significantly reduced, the balance achieved may be sufficient and the vehicle should be road tested to determine the effect on the vibration concern. If necessary, continue to move the position of the clamp heads an equal distance on either side of the light spot to a maximum of 120 degrees apart from each other, until the greatest amount of reduction in the vibration disturbance is achieved. If the amount of disturbance to the propeller shaft appears to be almost unchanged or even increased, proceed to step 14.
14. Add a third clamp to the propeller shaft, next to the first and second clamps and with the head of the clamp directly on the light spot.
15. Observe the amount of disturbance to the propeller shaft. If the amount of disturbance to the propeller shaft appears to be significantly reduced, the balance achieved may be sufficient and the vehicle should be road tested to determine the effect on the vibration concern. If necessary, continue to move the position of the first and second clamp heads an equal distance on either side of the light spot to a maximum of 120 degrees apart from each other, until the greatest amount of reduction in the vibration disturbance is achieved. If the amount of disturbance to the propeller shaft appears to be almost unchanged or even increased after a third clamp was used on the propeller shaft, the propeller shaft likely requires replacement.
16. If the heavy spot of the propeller shaft could not be identified, install a band-type hose clamp to the propeller shaft as a weight, with the head of the clamp directly in-line with an existing factory-installed weight.
17. Observe the amount of disturbance to the propeller shaft. If the amount of disturbance to the propeller shaft appears to be significantly reduced, the balance achieved may be sufficient and the vehicle should be road tested to determine the effect on the vibration concern. The head of the clamp can be moved very slightly, if necessary to refine the balance achieved. If the amount of disturbance to the propeller shaft appears to be almost unchanged or even increased, proceed to step 18.
18. Move the head of the clamp 180 degrees, directly opposite the factory-installed weight.
19. Observe the amount of disturbance to the propeller shaft. If the amount of disturbance to the propeller shaft appears to be significantly reduced, the balance achieved may be sufficient and the vehicle should be road tested to determine the effect on the vibration concern. The head of the clamp can be moved very slightly, if necessary to refine the balance achieved. If the amount of disturbance to the propeller shaft appears to be almost unchanged or even increased, the propeller shaft may require replacement.

Driveline Working Angles Adjustment

Rear axle wind-up may cause launch shudder even when all of the working angles are within specifications. Rear axle wind-up occurs when heavy torque during acceleration causes the pinion nose to point upward. In order to compensate for axle wind-up, tip the pinion nose downward. Install the axle shims incrementally, performing a road test after each shim. Add shims until the road test indicates that the shudder is eliminated.

Wedge shims of different sizes are available through the parts' system and independent suppliers for the purpose of shimming the rear axle angle. Wedge shims are available in 2, 3, and 4 degrees.

Scheme 65

1. Choose a wedge shim based on the Measuring Propeller Shaft Angle Procedure.
2. Remove the U-bolt. Refer to Leaf Spring Replacement in Rear Suspension.
3. Install the shims (5) in order to increase or decrease the angle of the rear axle pinion. Install the shims between the leaf spring (3) and the spring seat (2). Important After installing the shims, ensure that the U-bolt has 2 or 3 threads above the nut. Ensure also that the center bolt, located in the spring seat, is long enough to seat in the locator hole. If these 2 conditions do not exist, use longer U-bolts and center bolts. Longer U-bolts and center bolts are available through local spring shops.
4. Install the U-bolt. Refer to Leaf Spring Replacement in Rear Suspension.

Scheme 66

If a transmission requires shims, order the shims through the parts distribution system.

Installing most shims will change the transmission angle approximately 1/2 degree.

When shimming transmissions, use a shim made from steel stock at the necessary thickness. Ensure that the shim contacts the full width of the area to be shimmed. Do not use washers.

One Piece Propeller Shaft Phasing Correction

An out of phase single-piece propeller shaft is very unusual. If the shaft is visibly out of place, the end yokes are welded on in the wrong position, or the shaft is damaged due to twisting, the propeller shaft requires replacement.

Multiple-Piece Propeller Shaft Phasing Correction

There are two possible causes for an out of phase multiple-piece propeller shaft

1. Inspect the shaft to see if it is visibly out of place, the end yokes are welded on in the wrong position, or the shaft is damaged due to twisting. If any of these conditions apply, the propeller shaft requires replacement.
2. If the propeller shaft assembly has no visual physical defects and the propeller shaft phasing inspection procedure indicated that the propeller shafts were out of phase, perform the following: Remove the yoke from the spline shaft and determine if it is possible to correct the out of phase condition by reinstalling the yoke on a different position on the spline shaft. If it is possible to reinstall the yoke on a different position on the spline shaft, determine the correct location, reinstall the yoke to the spline shaft, and reinspect the phasing of the propeller shafts. If it is not possible to reinstall the yoke on a different position on the spline shaft and the propeller shaft phasing inspection procedure indicated that the propeller shafts were out of phase, the defective propeller shaft requires replacement.

Vibration Theory

The designs and engineering requirements of vehicles have undergone drastic changes over the last several years.

Vehicles are stiffer and provide more isolation from road input than they did previously. The structures of today's stiffer vehicles are less susceptible to many of the vibrations which could be present in vehicles of earlier designs, however, vibrations can still be detected in a more modern vehicle if a transfer path is created between a rotating component and the body of the vehicle.

There are not as many points of isolation from the road in many vehicles today. If a component produces a strong enough vibration, it may overcome the existing isolation and the component needs to be repaired or replaced.

The presence/absence of unwanted noise and vibration is linked to the customer's perception of the overall quality of the vehicle.

Vibration is the repetitive motion of an object, back and forth, or up and down. The following components cause most vehicle vibrations

1. A rotating component
2. The engine combustion process firing impulses

Rotating components will cause vibrations when excessive imbalance or runout is present. During vibration diagnosis, the amount of allowable imbalance or runout should be considered a TOLERANCE and not a SPECIFICATION. In other words, the less imbalance or runout the better.

Rotating components will cause a vibration concern when they not properly isolated from the passenger compartment: Engine firing pulses can be detected as a vibration if a motor mount is collapsed.

A vibrating component operates at a consistent rate (km/h, mph, or RPM). Measure the rate of vibration in question. When the rate/speed is determined, relate the vibration to a component that operates at an equal rate/speed in order to pinpoint the source. Vibrations also tend to transmit through the body structure to other components. Therefore, just because the seat vibrates does not mean the source of vibration is in the seat.

Vibrations consist of the following three elements

1. The source - the cause of the vibration
2. The transfer path - the path the vibration travels through the vehicle
3. The responder - the component where the vibration is felt

Scheme 67

In the preceding picture, the source is the unbalanced tire. The transfer path is the route the vibrations travels through the vehicle's suspension system into the steering column. The responder is the steering wheel, which the customer reports as vibrating. Eliminating any one of these three elements will usually correct the condition. Decide, from the gathered information, which element makes the most sense to repair. Adding a brace to the steering column may keep the steering wheel from vibrating, but adding a brace is not a practical solution. The most direct and effective repair would be to properly balance the tire.

Scheme 68

Vibration can also produce noise. As an example, consider a vehicle that has an exhaust pipe grounded to the frame. The source of the vibration is the engine firing impulses traveling through the exhaust. The transfer path is a grounded or bound-up exhaust hanger. The responder is the frame. The floor panel vibrates, acting as a large speaker, which produces noise. The best repair would be to eliminate the transfer path. Aligning the exhaust system and correcting the grounded condition at the frame would eliminate the transfer path.

Basic Vibration Terminology

The following are the 2 primary components of vibration diagnosis

1. The physical properties of objects
2. The object's properties of conducting mechanical energy

The repetitive up and down or back and forth movement of a component cause most customer vibration complaints. The following are the common components that vibrate

1. The steering wheel
2. The seat cushion
3. The frame
4. The IP

Vibration diagnosis involves the following simple outline

1. Measure the repetitive motion and assign a value to the measurement in cycles per second or cycles per minute.
2. Relate the frequency back on terms of the rotational speed of a component that is operating at the same rate or speed.
3. Inspect and test the components for conditions that cause vibration.

For example, performing the following steps will help demonstrate the vibration theory

Scheme 69

1. Clamp a yardstick to the edge of a table, leaving about 50 cm (20 in) hanging over the edge of the table.
2. Pull down on the edge of the stick and release while observing the movement of the stick.

The motion of the stick occurs in repetitive cycles. The cycle begins at midpoint, continues through the lowest extreme of travel, then back past the midpoint, through the upper extreme of travel, and back to the midpoint where the cycle begins again.

The cycle occurs over and over again at the same rate, or frequency. In this case, about 10 cycles in one minute. If we measure the frequency to reflect the number of complete cycles that the yardstick made in one minute, the measure would be 10 cycles x 60 seconds = 600 cycles per minute (cpm).

We have also found a specific amount of motion, or amplitude, in the total travel of the yardstick from the very top to the very bottom. Redo the experiment as follows

1. Reclamp the yardstick to the edge of a table, leaving about 25 cm (10 in) hanging over the edge of the table.
2. Pull down on the edge of the stick and release while observing the movement of the stick.

The stick vibrates at a much faster frequency: 30 cycles per second (1,800 cycles per minute).

Scheme 70

Scheme 71

The word cycle comes from the same root as the word circle. A circle begins and ends at the same point, as thus, so does a cycle. All vibrations consist of repetitive cycles.

Scheme 72

Frequency is defined as the rate at which an event occurs during a given period of time. With a vibration, the event is a cycle, and the period of time is 1 second. Thus, frequency is expressed in cycles per second.

The proper term for cycles per seconds is Hertz (Hz). This is the most common way to measure frequency. Multiply the Hertz by 60 to get the cycles or revolutions per minute (RPM).

Scheme 73

Amplitude is the maximum value of a periodically varying quantity. Used in vibration diagnostics, we are referring it to the magnitude of the disturbance. A severe disturbance would have a high amplitude; a minor disturbance would have a low amplitude.

Amplitude is measured by the amount of actual movement, or the displacement. For example, consider the vibration caused by an out-of-balance wheel at 80 km/h (50 mph) as opposed to 40 km/h (25 mph). As the speed increases, the amplitude increases.

Free Vibration

Free vibration is the continued vibration in the absence of any outside force. In the yardstick example, the yardstick continued to vibrate even after the end was released.

Forced Vibration

Forced vibration is when an object is vibrating continuously as a result of an outside force.

Scheme 74

A spinning object with an imbalance generates a centrifugal force. Performing the following steps will help to demonstrate centrifugal force

1. Tie a nut to a string.
2. Hold the string. The nut hangs vertically due to gravity.
3. Spin the string. The nut will spin in a circle.

Centrifugal force is trying to make the nut fly outward, causing the pull you feel on your hand. An unbalanced tire follows the same example. The nut is the imbalance in the tire. The string is the tire, wheel, and suspension assembly. As the vehicle speed increases, the disturbing force of the unbalanced tire can be felt in the steering wheel, the seat, and the floor. This disturbance will be repetitive (Hz) and the amplitude will increase. At higher speeds, both the frequency and the amplitude will increase. As the tire revolves, the imbalance, or the centrifugal force, will alternately lift the tire up and force the tire downward, along with the spindle, once for each revolution of the tire.

Scheme 75

The natural frequency is the frequency at which an object tends to vibrate. Bells, guitar strings, and tuning forks are all examples of objects that tend to vibrate at specific frequencies when excited by an external force.

Suspension systems, and even engines within the mounts, have a tendency to vibrate at certain frequencies. This is why some vibration complaints occur only at specific vehicle speeds or engine RPM.

The stiffness and the natural frequency of a material have a relationship. Generally, the stiffer the material, the higher the natural frequency. The opposite is also true. The softer a material, the lower the natural frequency. Conversely, the greater the mass, the lower the natural frequency.

Scheme 76

All objects have natural frequencies. The natural frequency of a typical automotive front suspension is in the 10-15 Hz range. This natural frequency is the result of the suspension design. The suspension's natural frequency is the same at all vehicle speeds. As the tire speed increases along with the vehicle speed, the disturbance created by the tire increases in frequency. Eventually, the frequency of the unbalanced tire will intersect with the natural frequency of the suspension. This causes the suspension to vibrate. The intersecting point is called the resonance.

The amplitude of a vibration will be greatest at the point of resonance. While the vibration may be felt above and below the problem speed, the vibration may be felt the most at the point of resonance.

Scheme 77

Damping is the ability of an object or material to dissipate or absorb vibration. The automotive shock absorber is a good example. The function of the shock absorber is to absorb or dampen the oscillations of the suspension system.

Scheme 78

Two separate disturbances that are relatively close together in frequency will lead to a condition called beating, or phasing. A beating vibration condition will increase in intensity or amplitude in a repetitive fashion as the vehicle travels at a steady speed. This beating vibration can produce the familiar droning noise heard in some vehicles.

Beating occurs when 2 vibrating forces are adding to each other's amplitude. However, 2 vibrating forces can also subtract from each other's amplitude. The adding and subtracting of amplitudes in similar frequencies is called beating. In many cases, eliminating either one of the disturbances can correct the condition.

Order

Order refers to how many times an event occurs during 1 revolution of a rotating component.

Scheme 79

For example, a tire with 1 high spot would create a disturbance once for every revolution of the tire. This is called first-order vibration.

Scheme 80

An oval-shaped tire with 2 high spots would create a disturbance twice for every revolution. This is called second-order vibration. Three high spots would be third-order, and so forth. Two first-order vibrations may add or subtract from the overall amplitude of the disturbance, but that is all. Two first-order vibrations do not equal a second-order. Due to centrifugal force, an unbalanced component will always create at least a first-order vibration.

J 38792-A Electronic Vibration Analyzer

The J 38792-A, electronic vibration analyzer (EVA), is a 12-volt powered hand-held device, similar to a scan tool, which receives input from an attached vibration sensor or accelerometer and displays the most dominate input frequency(ies) (up to three) on its liquid crystal display. The vibration concern frequency(ies) are obtained through the use of the J 38792-A while following the Vibration Analysis Diagnostic Tables. The frequency(ies) obtained, when applied to the Vibration Analysis Diagnostic Tables, are used as a primary input to help determine the source of the vibration concern.

EVA Vibration Sensor

The J 38792-A vibration sensor incorporates a 6.1 m (20 ft) cord, that allows the sensor to be placed on virtually any component of the vehicle where a vibration concern is felt.

The J 38792-A contains 2 sensor input ports which can be activated individually to allow for 2 individual vibration sensor inputs. The vibration sensors can then be placed in 2 different locations in the vehicle and their individual inputs can be read without having to stop a test, move the sensor and resume the test. The use of 2 vibration sensors can help in more quickly finding and recording an accurate frequency of the vibration concern, and in more quickly making comparisons between 2 different areas of a single component, or a vehicle system, during the diagnostic process.

EVA Vibration Sensor Placement

Proper placement of the J 38792-A vibration sensor (accelerometer) is critical to ensure that proper vibration readings are obtained by the J 38792-A. The vibration sensor should be placed on the specific vehicle component identified as being the most respondent to the vibration. If no component has been identified, install the sensor to the steering column as a starting point.

EVA Vibration Sensor-to-Component Attachment

The vibration sensor of the J 38792-A is designed to pickup disturbances which primarily occur in the vertical plane, since most vibrations are felt in that same up-and-down direction. The J 38792-A vibration sensor is therefore directional sensitive and must be attached to vehicle components such that the side of the sensor marked UP is always facing upright and the sensor body is as close to horizontal as possible. The sensor must be installed in the exact same position each time tests are repeated or comparisons are made to other vehicles.

The J 38792-A vibration sensor can be attached to vehicle components in various ways. For non-ferrous surfaces, such as the shroud of a steering column, the sensor can be attached using putty, or hook and loop fasteners. For ferrous surfaces, the sensor can be attached using a magnet supplied with the sensor.

EVA Software Cartridge

The J 38792-A uses a software cartridge, the J 38792-60, which provides various information to the J 38792-A. The J 38792-60 provides the J 38792-A with an additional feature which can be selected and utilized to assist in diagnosing vibration concerns.

This support-feature is available through the J 38792-A Auto-Mode function. When selected, the J 38792-A will prompt the user to select which one of 2 vehicle systems (vehicle speed or engine speed), is the SUSPECTED source of the vibration concern. Using the inputted vehicle data parameters along with the most dominate vibration frequency obtained, it will identify a SUSPECTED source of the vibration concern, such as first-order tire and wheel. This can be a useful feature when used in conjunction with the Vibration Analysis Diagnostic Tables, to confirm results obtained through the diagnostic process.

EVA Smart Strobe Function

The J 38792-A can be used to identify some rotating components/systems which exhibit imbalance IF the component rotational speed is the dominant frequency of the vibration concern. The J 38792-A is equipped with a strobe light trigger wire which can be used with an inductive pickup timing light, J 38792-25, or equivalent included with the J 38792-KIT, or available separately. Using the Smart Strobe function enables the user to input the vibration frequency to which the strobe will flash. By marking the suspected rotating component, such as a pulley, adjusting the strobe frequency to match the dominant vibration frequency at the engine RPM noted during diagnosis, and then operating the engine at that specific RPM, the mark on the object will appear to be stationary if that object is imbalance.

EVA Strobe Balancing Function

The J 38792-A can be used to identify the light spot on a propeller shaft IF the propeller shaft rotational speed is the dominant frequency of the vibration concern. The J 38792-A is equipped with a strobe light trigger wire which can be used with an inductive pickup timing light, J 38792-25, or equivalent included with the J 38792-KIT, or available separately, and in conjunction with the J 38792-A vibration sensor to identify the light spot on a propeller shaft and to help in making a determination as to when propeller shaft balance is obtained.

Averaging/Non-Averaging Modes

The EVA provides 2 modes of displaying the most dominate frequencies which the EVA vibration sensor (accelerometer) detects; averaging and non-averaging (instantaneous).

The averaging mode uses multiple vibration samples taken over a period of time and then displays the most dominant frequencies which have been averaged-out. Using the averaging mode minimizes the distractions caused by a sudden vibration frequency being displayed that is not related to the concern vibration, such as from pot holes or from uneven road surfaces.

The non-averaging (instantaneous) mode is more sensitive to vibration disturbances than the averaging mode. Using the non-averaging mode will generate instantaneous frequency displays which are not averaged across multiple samples over a period of time; the specific vibration frequencies that occur at a specific moment during diagnostic testing will be displayed at that moment. The non-averaging (instantaneous) mode is useful when measuring a vibration disturbance that exists for only a short period of time or during acceleration/deceleration testing.

When operating the EVA in the averaging mode along with the Auto Mode, "A" will be displayed along the top of the screen to the left of the vibration sensor input port being used. When operating the EVA in the averaging mode and the Manual Mode, "AVG" will be displayed along the top center of the screen.

When operating the EVA in the non-averaging (instantaneous) mode along with the Auto Mode, "I" will be displayed along the top of the screen to the left of the vibration sensor input port being used. When operating the EVA in the non-averaging (instantaneous) mode and the Manual Mode, the top center of the screen will be blank.

Scheme 81

The most dominant input frequencies, up to three, received from the J 38792-A vibration sensor, are displayed in descending order of amplitude strength.

The frequency readings are displayed along the left side of the screen, followed to the right by either a bar graph or the suspected source of the vibration - depending upon the mode selected, then the amplitude reading for each frequency along the right side of the screen. The top row of the screen indicates the units of measure being displayed for the frequencies along the left side and for the amplitudes along the right side. The top row also indicates the vibration sensor input port which was selected on the keypad (A or B) and which mode was selected: averaging or non-averaging (instantaneous).

The frequency(ies) can be displayed in either revolutions per minute (RPM) or revolutions per second; Hertz (Hz). The selected display type (RPM or Hz) will be indicated at the left side of the screen, above the frequency readings.

When the AUTO MODE function is not in use, a bar graph is displayed next to each frequency to provide a quick visual indication of the relative amplitude strength.

When the AUTO MODE function is being used, the suspected source of the vibration is displayed next to each frequency to provide support to the diagnostic process.

The actual amplitude strength of each frequency is displayed at the right side of the screen and shown in G's-of-acceleration force.

Vibrate Software Description and Operation

The J 38792-VS, Vibrate Software, is a computer software program which is designed to be used in support of the Vibration Analysis diagnostic tables, along with the J 38792-A, Electronic Vibration Analyzer (EVA) and a scan tool, to help in determining the source of a vibration concern. The J 38792-VS is designed to provide quick calculations and produce a chart of the rotational speeds and frequency ranges for specific vehicle systems and components, based upon vehicle data parameters inputted by the user.

The J 38792-VS uses the vehicle data parameters, such as axle ratio, number of engine cylinders, etc. to create the base chart, depicting the relationships of the various vehicle systems and/or components. The chart view can be modified to show data related to vehicle speed only, engine speed only, or both vehicle speed and engine speed. The user can then plot the dominant frequency reading obtained on the J 38792-A which correlates with the vibration concern, and the engine RPM obtained on a scan tool which correlates with the concern. Once these pieces of data are correctly plotted, the chart will point to the source of the vibration concern, which should confirm the results obtained through the following the Vibration Analysis diagnostic tables.

Scheme 82

The reed tachometer consists of 2 rows of reeds arranged side-by-side. Each reed is tuned to vibrate or resonate when it is excited by a specific frequency. The reeds are arranged by their specific resonant frequency, increasing from left to right, ranging from 10-80 Hz. This arrangement allows for a visual display of the most dominate frequencies which fall within this range.

The reed tachometer can be a helpful diagnostic tool, however it is extremely sensitive to external inputs that are not related to the vibration concern, such as rough road surfaces, etc., and it is difficult to master its use. Due to these conditions, the reed tachometer has limited diagnostic capability.

Due to the limited diagnostic capability, limited availability and increasing costs of the reed tachometer, it is NOT recommended as the primary tool to use in diagnosing a vibration concern.

When diagnosing a vibration concern, use the J 38792-A, electronic vibration analyzer (EVA). The J 38792-A has been designed to overcome the shortcomings to the reed tachometer. Refer to Electronic Vibration Analyzer (EVA) Description and Operation.

Scheme 83

Scheme 84

Scheme 85

See also:
• WORK STALL TEST CAUTION