Vibration - Drivetrain Buick Century VI

DESCRIPTION & OPERATION

Note. This covers GENERAL MOTORS vehicles only. Other manufacturers offer generic information & procedure.

4-Wheel Drive/All Wheel Drive

Front axle shafts are flexible assemblies which consist of the following components

1. Constant velocity joint outer joint.
2. Tri-pot joint inner joint.
3. The front axle shaft connects the tri-pot inner joint and the constant velocity outer joint.
4. Axle shaft seal cover (1500 series).
5. The tri-pot joint is completely flexible, and moves with an in and out motion.
6. The constant velocity joint is flexible but can not move in and out.

The axle shaft is a balanced shaft that transmits rotational force from the front differential to the front wheels when the transfer case is engaged. The axle shaft is mounted to the front differential by bolting the flange of the axle shaft to the flange on the inner output shaft of the front differential. The other end of the axle shaft is splined to fit into and drive the hub assembly when the transfer case is engaged. The tri-pot joint and constant velocity joint on the axle shaft allows the shaft to be flexible to move with the suspension travel of the vehicle.

Front Wheel Drive

Front axle shafts are flexible assemblies and consist of the following components

1. A front axle shaft constant velocity or tri-pot type joint (inner joint).
2. A front axle shaft constant velocity joint (outer joint).
3. A front axle shaft. The front axle shaft connects the front axle shaft tri-pot joint and the front axle shaft constant velocity joint.

The front axle shaft inner joint is completely flexible. The inner joint can move in and out. The front axle shaft outer joint is flexible, but the outer joint cannot move in and out.

Boots (Seals) & Clamps

The shaft boots (seals) in the front axle are made of a thermoplastic material. The clamps in front axle are made of stainless steel. The boot (seal) provides the following functions

1. To protect the internal parts of the inboard and outboard joint by protecting the grease from surrounding detrimental atmospheric conditions such as extreme temperatures, ozone gas, etc.
2. To protect the internal parts of the inboard and outboard joint by protecting the grease from foreign materials such as stones, dirt, water, salt, etc.
3. Allows angular movement and the axial movement of the front axle shaft inner joint.
4. Allows angular movement of the front axle shaft outer joint.

Note. Protect the boots (seals) from sharp tools and from the sharp edges of the surrounding components. Any damage to the boots (seals) or the clamps will result in leakage. Leakage will allow water to leak into the front axle shaft joints. Leakage will also allow grease to leak out of the joints. Leakage may cause noisy front axle operation and eventual failure of the internal components.

The clamps provide a leak proof connection for the front axle shaft joints at the following locations

1. The housing.
2. The front axle shaft.

The thermoplastic material performs well under normal conditions and normal operation. However, the material is not strong enough to withstand the following conditions

1. Abusive handling.
2. Damage from sharp objects (such as sharp tools or any sharp edges of the surrounding components in the vehicle).

Inner Joint

The front axle shaft tri-pot joint is made with the tri-pot design without an over-extension limitation retainer. The front axle inner joint is splined to interlock with the transaxle.

Outer Joint

The front axle shaft constant velocity joint is made with the Rzeppa joint design. The shaft end (which mates with the knuckle/hub) has a helical spline. The helical spline ensures a tight, press-type fit. This design prevents end play between the hub bearing and the front axle.

Rear Wheel Drive With Independent Rear Suspension

Drive axles are flexible assemblies consisting of an inner and outer constant velocity (CV) joint connected by an axle shaft. The inner joint is completely flexible, and can move in and out. The outer joint is also flexible, but cannot move in and out. These drive axles are used to transmit rotational force from the rear axle differential to the rear tire and wheel assemblies.

Seal & Clamp

The drive axle assemblies use inboard and outboard joint seals made of thermoplastic material, and clamps made of stainless steel. The functions of the seals are as follows

1. The seals protect the internal parts of the inboard and outboard joints. They protect the joint lubricating grease from surrounding detrimental atmospheric conditions (such as extreme temperatures, ozone gas, etc.). They protect the joint lubricating grease from foreign materials (such as stones, dirt, water, salt, etc.).
2. The seals facilitate angular and axial movement of the inboard joint.
3. The seals facilitate angular movement of the outboard joint.

The function of the clamps is as follows

1. Provide a leak proof connection at both the housing and the axle shaft for the inboard and outboard joints.
2. The thermoplastic material performs well against normal handing, operational wear and conditions. This material however, is not strong enough to withstand abusive handling or damage due to objects such as sharp tools or the sharp edge of any other surrounding component on the vehicle.

Inner Joint

The inner joints are of the enhanced double offset design. The inner joints use a female spline which is installed over a stub shaft protruding from the rear axle differential.

Outer Joint

The outer joints are of the Rzeppa joint design. The splined shaft end which mates with the knuckle and hub assembly, incorporates a helical spline to assure a tight, press-type fit. This design assures that no end play will exist between the hub bearing and the drive shaft assembly for added durability and reduced bearing noise.

Selectable Four Wheel Drive (S4WD) Front Differential Assembly

The Selectable Four Wheel Drive (S4WD) front differential assembly consist of the following components.

1. Differential Carrier Housing
2. Differential Assembly
3. Output Shafts (Left and Right Side)
4. Inner Axle Shaft Housing
5. Inner Axle Shaft (Right Side)
6. Clutch Fork
7. Clutch Fork Sleeve
8. Electric Motor Actuator

The front differential assembly on Selectable Four Wheel Drive (S4WD) model vehicles uses a central disconnect feature in order to engage and disengage the front differential assembly. When the driver engages the 4WD system, the transfer case control module sends a signal to the electric motor actuator to energize and extend the plunger inside. The extended plunger moves the clutch fork and clutch fork sleeve across the inner axle shaft and the clutch fork shaft and locks the 2 shafts together. The locking of the 2 shafts allows the axle to operate in the same manner as a semi-floating rear axle. A driveshaft connects the transfer case to the front differential assembly. The differential carrier assembly uses a conventional ring and pinion gear set to transmit the driving force of the engine to the wheels. The open differential allows the wheels to turn at different rates of speed while the axle continues to transmit the driving force. This prevents tire scuffing when going around corners and premature wear on internal axle parts. The ring and pinion set and the differential are contained within the carrier. The axle identification number is located on top of the differential carrier assembly or on a label on the bottom of the right half of differential carrier assembly. The drive axles are completely flexible assemblies consisting of inner and outer constant velocity (CV) joints protected by thermoplastic boots and connected by a axle shaft.

Full-Time Four Wheel Drive (F4WD) Front Differential Assembly

The Full-Time Four Wheel Drive (F4WD) Front Differential Assembly consist of the following components.

1. Differential Carrier Housing
2. Differential Assembly
3. Output Shaft (Left Side)
4. Inner Axle Shaft Housing
5. Inner Axle Shaft (Right Side)

The front differential assembly on Full-Time Four Wheel Drive (F4WD) model vehicles does not have a central disconnect feature in order to engage and disengage the front differential assembly. The left and right axle shafts are connected directly to the differential case assembly. This allows the axle shafts and the driveshaft to spin continuously. The transfer case controls the amount of torque applied to the front differential assembly. The remaining components are the same as the Selectable Four Wheel Drive axle.

DRIVESHAFT

The driveshaft is a tube with universal joints at both ends which DO NOT require periodic maintenance, that transmit power from the transfer case or transmission output shaft to the differential.

Front Driveshaft Description

The front driveshaft transmits rotating force from the transfer case to the front differential when the transfer case is engaged. The front driveshaft connects to the transfer case using a splined slip joint.

One Piece Driveshaft Description

A one piece driveshaft uses a splined slip joint to connect the driveline to the transmission or transfer case.

Two Piece Driveshaft Description

There are 3 universal joints used on the 2 piece driveshaft, A center bearing assembly is used to support the driveshaft connection point, and help isolate the vehicle from vibration.

Driveshaft Phasing Description

The driveshaft is designed and built with the yoke lugs (ears) in line with each other. This produces the smoothest running shaft possible. A driveshaft designed with built in yoke lugs in line is known as in-phase. An out of phase driveshaft often causes vibration. The driveshaft generates vibration from speeding up and slowing down each time the universal joint goes around. The vibration is the same as a person snapping a rope and watching the wave reaction flow to the end. An in phase driveshaft is similar to 2 persons snapping a rope at the same time and watching the waves meet and cancel each other out. A total cancellation of vibration produces a smooth flow of power in the drive line. All splined shaft slip yokes are keyed in order to ensure proper phasing.

Universal Joint Description

The universal joint is connected to the driveshaft. The universal consist of 4 caps with needle bearings and grease seals mounted on the trunnions of a cross or spider. These bearings and caps are greased at the factory and no periodic maintenance is required. There are 2 universal joints used in a one piece driveshaft and 3 used in 2 piece driveshaft. The bearings and caps are pressed into the yokes and held in place with snap rings, except for 2 bearings on some models witch are strapped onto the pinion flange of the differential. Universal joints are designed to handle the effects of various loads and rear axle windup conditions during acceleration and braking. The universal joint operates efficiently and safely within the designed angle variations. When the design angles are exceeded, the operational life of the joint decreases.

Center Bearing Description

Center bearings support the driveline when using 2 or more driveshafts. The center bearing is a ball bearing mounted in a rubber cushion that attaches to a frame crossmember. The manufacturer pre-lubricates and seals the bearing. The cushion allows vertical motion at the driveline and helps isolate the vehicle from vibration.

Standard Differential

Rear differential assembly can consist of the following components.

1. Differential Axle Housing
2. Differential Carrier
3. Right & Left Axle Tubes
4. Right & Left Axle Shafts

These differential assembly is either full-floating or semi-floating. These differential can be identified as follows

1. The semi-floating differential has axle shafts with C-Clips inside the differential carrier on the inner ends of the axle shafts.
2. The full-floating differential has bolts at the hub retaining the axle shafts to the hub assembly.

The differential can be identified by the stamping on the right side axle tube They may also be identified by the ring gear size. The limited slip/locking differential information for these rear differentials can be located in the appropriate LIMITED SLIP/LOCKING DIFFERENTIAL article in DRIVELINE/AXLES.

A open differential has a set of 4 gears. Two are side gears and 2 are pinion gears. Some differentials have more than 2 pinion gears. Each side gear is splined to an axle shaft so each axle shaft turns when it's side gear rotates. The pinion gears are mounted on a differential pinion shaft, and the gears are free to rotate on this shaft. The pinion shaft is fitted into a bore in the differential case and is at right angles to the axle shafts. Power is transmitted through the differential as follows

1. The drive pinion rotates the ring gear.
2. The ring gear being bolted to the differential case, rotates the case.
3. The differential pinion, as it rotates the case, forces the pinion gears against the side gears.
4. When both wheels have equal traction, the pinion gears DO NOT rotate on the pinion shaft because of input force on the pinion gear is equally divided between the 2 side gears. Therefore, the pinion gears revolve with the pinion shaft, but does not rotate around the shaft itself.
5. The side gears, being splined to the axle shafts and in mesh with the pinion gears rotate the axle shafts. NOTE: If a vehicle were always driven in a straight line, the ring and pinion gears would be sufficient. The axle shaft could be solidly attached to the ring gear and both driving wheels would turn at equal speed. However, if it became necessary to turn a corner, the tires would scuff and slide because the differential allows the axle shafts to rotate at different speeds. When the vehicle turns a corner, the inner wheel turns slower than the outer wheel and slows it's rear axle side gear (as the shaft is splined to the side gear). The rear axle pinion gears will roll around the slowed rear axle side gear, driving the rear axle side gear wheel faster.

Locking Differential

The locking differential consists of the following components

1. Differential case; one or 2 piece.
2. Locking differential spider; 2 piece case only.
3. Pinion gear shaft; one piece case only.
4. Differential pinion gear shaft lock bolt; one piece case only.
5. 2 clutch discs sets.
6. Locking differential side gear.
7. Thrust block.
8. Locking differential clutch disc guides.
9. Differential side gear shim.
10. Locking differential clutch disc thrust washer.
11. Locking differential governor.
12. Latching bracket.
13. Cam plate assembly.
14. Differential pinion gears.
15. Differential pinion gear thrust washers.

The optional locking differential (RPO G80) enhances the traction capability of the rear axle by combining the characteristics of a limited-slip differential and the ability of the axle shafts to "lock" together when uneven traction surfaces exist. The differential accomplishes this in 2 ways. First by having a series of clutch plates at each side of the differential case to limit the amount of slippage between each wheel. Second, by using a mechanical locking mechanism to stop the rotation of the right differential side gear, or the left differential side gear on the 10.5 inch axle, in order to transfer the rotating torque of the wheel without traction to the wheel with traction. Each of these functions occur under different conditions.

Limited-Slip Function

Under normal conditions, when the differential is not locked, a small amount of limited-slip action occurs. The gear separating force developed in the right-hand (left-hand side on 10.5 inch axle) clutch pack is primarily responsible for this.

The operation of how the limited-slip function of the unit works can be explained when the vehicle makes a right-hand turn. Since the left wheel travels farther than the right wheel, it must rotate faster than the ring gear and differential case assembly. This results in the left axle and left side gear rotating faster than the differential case. The faster rotation of the left-side gear causes the pinion gears to rotate on the pinion shaft. This causes the right-side gear to rotate slower than the differential case.

Although the side gear spreading force produced by the pinion gears compresses the clutch packs, primarily the right side, the friction between the tires and the road surface is sufficient to overcome the friction of the clutch packs. This prevents the side gears from being held to the differential case.

Locking Function

Locking action occurs through the use of some special parts

1. A governor mechanism with 2 flyweights.
2. A latching bracket.
3. The left side cam plate and cam side gear.

When the wheel-to-wheel speed difference is 100 RPM or more, the flyweights of the governor will fling out and one of them will contact an edge of the latching bracket. This happens because the left cam side gear and cam plate are rotating at a speed different, either slower or faster, than that of the ring gear and differential case assembly. The cam plate has teeth on its outer diameter surface in mesh with teeth on the shaft of the governor.

As the side gear rotates at a speed different than that of the differential case, the shaft of the governor rotates with enough speed to force the flyweights outward against spring tension. One of the flyweights catches its edge on the closest edge of the latching bracket, which is stationary in the differential case. This latching process triggers a chain of events.

When the governor latches, it stops rotating. A small friction clutch inside the governor allows rotation, with resistance, of the governor shaft while one flyweight is held to the differential case through the latching bracket. The purpose of the governor's latching action is to slow the rotation of the cam plate as compared to the cam side gear. This will cause the cam plate to move out of its detent position.

The cam plate normally is held in its detent position by a small wave spring and detent humps resting in matching notches of the cam side gear. At this point, the ramps of the cam plate ride up on the ramps of the cam side gear, and the cam plate compresses the left clutch pack with a self-energizing action.

As the left clutch pack is compressed, it pushes the cam plate and cam side gear slightly toward the right side of the differential case. This movement of the cam side gear pushes the thrust block which compresses the right-hand side gear clutch pack.

At this point, the force of the self-energizing clutches and the side gear separating force combine to hold the side gears to the differential case in the locking stage.

The entire locking process occurs in less than one second. The process works with either the left or right wheel spinning, due to the design of the governor and cam mechanism. A torque reversal of any kind will unlatch the governor, causing the cam plate to ride back down to its detent position. Cornering or deceleration during a transmission shift will cause a torque reversal of this type. The differential unit returns to its limited-slip function.

The self-energizing process would not occur if it were not for the action of one of the left clutch discs. This energizing disc provides the holding force of the ramping action to occur. It is the only disc which is splined to the cam plate itself. The other splined discs fit on the cam side gear.

If the rotating speed of the ring gear and differential case assembly is high enough, the latching bracket will pivot due to centrifugal force. This will move the flyweights so that no locking is permitted. During vehicle driving, this happens at approximately 20 MPH and continues at faster speeds.

When comparing the effectiveness of the locking differential, in terms of percent-of-grade capability to open and limited-slip units, the locking differential has nearly 3 times the potential of the limited-slip unit under the same conditions.

Locking Differential Torque-Limiting Disc

The locking differential design was modified in mid-1986 to include a load-limiting feature to reduce the chance of breaking an axle shaft under abusive driving conditions. The number of tangs on the energizing disc in the left-hand clutch pack was reduced allowing these tangs to shear in the event of a high-torque engagement of the differential locking mechanism.

At the time of failure of the load-limiting disc, there will be a loud bang in the rear axle and the differential will operate as a standard differential with some limited-slip action of the clutch packs at low torques.

The service procedure, when the disc tangs shear, involves replacing the left-hand clutch plates and the wave spring. It is also necessary to examine the axle shafts for twisting because at high torques it is possible to not only shear the load-limiting disc, but to also twist the axle shafts.

Limited Slip Differential

The locking differential consists of the following components

1. Differential case.
2. Pinion gear shaft.
3. Differential pinion gear shaft lock pin.
4. 2 clutch discs sets.
5. Differential side gears.
6. Differential clutch disc guides.
7. Differential side gear shim.
8. Differential clutch disc thrust washer.
9. Differential pinion gears.
10. Differential pinion gear thrust washers.

In a conventional differential, if one wheel spins, the opposite wheel will generate only as much torque as the wheel with the least amount of traction. In a limited slip differential, part of the ring gear torque is transmitted through clutch packs which contain multiple discs. In operation, two forces engage the limited slip differential's clutches. The first is the pre-load force within the clutch packs. The second is the separating forces generated by the side gears as torque is applied through the ring gear. The limited slip design provides the action needed for turning corners and for driving in a straight line when traction is uneven. When one wheel loses traction, the clutch packs transfer additional torque to wheel having the most traction. Limited slip differential resist wheel spin on bumpy roads and provides greater pulling power when one wheel loses traction. If both wheels slip due to unequal traction, limited slip operation is normal. Also in extreme cases of unequal traction, the wheel with the least amount of traction may spin.

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 (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 3 elements

1. The SOURCE is the cause of the vibration.
2. The TRANSFER PATH is the path the vibration travels through the vehicle.
3. The RESPONDER is the component where the vibration is felt.

For example, the SOURCE could be an 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 3 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.

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 instrument panel.

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

1. Clamp a yardstick to the edge of a table, leaving about 20" (50 cm) 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 10" (25 cm) 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 (1800 cycles per minute).

Cycle

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 21)and (Scheme 22).

Scheme 21

Scheme 22

Frequency

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 one second. Thus, frequency is expressed in cycles per second. (Scheme 23) 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 23

Amplitude

Amplitude is the maximum value of a periodically varying quantity. (Scheme 24) 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 50 MPH as opposed to 25 MPH. As the speed increases, the amplitude increases.

Scheme 24

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.

Centrifugal Force Due To An Imbalance

A spinning object with an imbalance generates a centrifugal force. (Scheme 25) 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 25

Natural Or Resonant Frequency

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.

Resonance

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. (Scheme 26) 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 26

Damping

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.

Beating (Phasing)

Two separate disturbances that are relatively close together in frequency will lead to a condition called beating, or phasing. (Scheme 27) 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.

Scheme 27

Order

Order refers to how many times an event occurs during one revolution of a rotating component. For example, a tire with one high spot would create a disturbance once for every revolution of the tire. This is called first-order vibration.

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.

ELECTRONIC VIBRATION ANALYZER (EVA)

Note. Tools Required: Electronic Vibration Analyzer (J-38792-A).

The 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 frequencies (up to 3) on its liquid crystal display. The vibration concern frequencies are obtained through the use of the EVA while following the Vibration Analysis Diagnostic Tables. The frequencies 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 EVA vibration sensor incorporates a 20 ft (6.1m) cord, that allows the sensor to be placed on virtually any component of the vehicle where a vibration concern is felt.

The EVA 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 Electronic Vibration Analyzer (EVA) 2 (J-38792-A) vibration sensor (accelerometer) is critical to ensure that proper vibration readings are obtained by the EVA. 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

Note. The EVA vibration sensor must be attached to vehicle components in the manner indicated in order to achieve accurate frequency readings of the vibration disturbance.

The vibration sensor of the EVA 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 EVA 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 EVA 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 EVA uses a Software Cartridge (J-38792-60), which provides various information to the EVA. The software cartridge provides the EVA with an additional feature which can be selected and utilized to assist in diagnosing vibration concerns.

Note. The Auto-Mode function of the EVA software cartridge, is designed to be used in support of the Vibration Analysis Diagnostic Tables only.

This support-feature is available through the EVA Auto-Mode function. When selected, the EVA 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 EVA 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 EVA 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 unbalanced.

EVA Strobe Balancing Function

The EVA can be used to identify the light spot on a driveshaft IF the driveshaft rotational speed is the dominant frequency of the vibration concern. The EVA 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 EVA vibration sensor to identify the light spot on a driveshaft and to help in making a determination as to when driveshaft balance is obtained.

Averaging/Non-Averaging Modes

1. The Electronic Vibration Analyzer (EVA) provides 2 modes of displaying the most dominate frequencies which the EVA 2 (J-38792-A) vibration sensor (accelerometer) detects; averaging and non-averaging (instantaneous).
2. 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.
3. 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.
4. 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.
5. 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.

EVA Display

1. The most dominant input frequencies, up to 3, received from the Electronic Vibration Analyzer (EVA) 2 (J-38792-A) vibration sensor, are displayed in descending order of amplitude strength.
2. 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).
3. The frequencies 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.
4. 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.
5. 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.
6. The actual amplitude strength of each frequency is displayed at the right side of the screen and shown in G's-of-acceleration force.

The Vibrate Software (J-38792-VS), is a computer software program which is designed to be used in support of the Vibration Analysis diagnostic tables, along with the Electronic Vibration Analyzer (EVA) (J-38792-A), and a scan tool, to help in determining the source of a vibration concern. The vibrate software 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 vibrate software 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 EVA 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.

Description

1. 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.
2. 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.
3. 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.
4. When diagnosing a vibration concern, use the Electronic Vibration Analyzer (EVA) 2 (J-38792-A). The EVA has been designed to overcome the shortcomings to the reed tachometer. See «ELECTRONIC VIBRATION ANALYZER (EVA)»(/buick/century/vi-1997-2005/remont/axle-shafts/#vibration-drivetrain__electronic-vibration-analyzer-eva) under DESCRIPTION & OPERATION.

VIBRATION DIAGNOSIS & CORRECTION

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

1. See «VIBRATION ANALYSIS - ROAD TESTING»(/buick/century/vi-1997-2005/remont/axle-shafts/#vibration-drivetrain__vibration-analysis-road-testing) 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 and 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 Electronic Vibration Analyzer (EVA) 2 (J-38792-A), and the Vibrate Software (J-38792-VS). 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: See «VIBRATION THEORY & TERMINOLOGY»(/buick/century/vi-1997-2005/remont/axle-shafts/#vibration-drivetrain) under DESCRIPTION & OPERATION. See «ELECTRONIC VIBRATION ANALYZER (EVA)»(/buick/century/vi-1997-2005/remont/axle-shafts/#vibration-drivetrain__electronic-vibration-analyzer-eva) under DESCRIPTION & OPERATION. See «VIBRATE SOFTWARE»(/buick/century/vi-1997-2005/remont/axle-shafts/#vibration-drivetrain) under DESCRIPTION & OPERATION. See «REED TACHOMETER»(/buick/century/vi-1997-2005/remont/axle-shafts/#vibration-drivetrain) under DESCRIPTION & OPERATION.

Vibration Diagnostic Process

Note. Using the following steps of the vibration diagnostic process will help you to effectively narrow-down and pinpoint 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»(/buick/century/vi-1997-2005/remont/axle-shafts/#vibration-drivetrain__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 and 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 .

COMPONENT ROTATIONAL SPEED CALCULATION

Note. Tools Required: Electronic Vibration Analyzer (EVA) 2 (J-38792-A).

A size P235/75R15 tire rotates one complete Revolution Per Second (RPS), or one Hz, at a vehicle speed of 5 MPH. This means that at 10 MPH, the same tire will make 2 complete revolutions in one second, 2 Hz, and so on.

Tire & Wheel Rotational Speed Calculation

1. At 5 MPH, a vehicle will travel approximately 88" (7.333 ft) per second. To determine the distance around the tire/wheel combination (circumference) make a vertical mark on the tire with chalk and a corresponding mark on the ground. Move the vehicle forward or backward until mark is pointing towards the ground again (360 degrees) and mark ground again. Measure distance between both marks to determine the circumference around the tire/wheel combination. Divide 88 (inches per second at 5 MPH) by the circumference of each tire to determine the RPS, or Hz at 5 MPH.
2. Determine the number of increments of 5 MPH that are present, based on the vehicle speed (MPH) at which the disturbance occurs. For example: Assume that a disturbance occurs at a vehicle speed of 60 MPH. A speed of 60 MPH has 12 increments of 5 MPH: 60 MPH divided by 5 MPH = 12 increments.
3. Determine the rotational speed of the tires in revolutions per second (Hz), at the specific vehicle speed (MPH) at which the disturbance occurs. For example: To determine the tire rotational speed at 60 MPH, multiply the number of increments of 5 MPH by the revolutions per second (Hz) for one increment: 12 increments X 1.12 Hz = 13.44 Hz, rounded to 13 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 EVA 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: 13 Hz X 2, for second order = 26 Hz second-order tire/wheel assembly rotation related 13 Hz X 3, for third order = 39 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.

Driveline Rotational Speed Calculation

1. Determine the first order rotational speed of the driveline/transmission output shaft/rear axle pinion gear, in revolutions per second (Hz), based on the first-order rotational speed of the tire/wheel assemblies and the drive axle ratio. 13 Hz X 3.42 drive axle ratio = 44.46 Hz, rounded to 44 Hz first-order driveline rotation related.
2. Compare the rotational speed of the driveline/transmission output shaft/rear axle pinion gear, at the specific vehicle speed at which the disturbance occurs, to the dominant frequency recorded on the Electronic Vibration Analyzer (EVA) 2 during testing. If the frequencies match, then a first-order disturbance related to the rotation of the driveline/transmission output shaft/rear axle pinion gear, is present.

Component Rotational Speed Worksheet

1. Utilize the following worksheet as an aid in calculating the first, second and third order of tire/wheel assembly rotational speed and the first order of driveline (transmission output shaft/rear axle pinion gear) rotational speed related disturbances that may be present in the vehicle. (Scheme 28)
2. 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 1-5 MPH of speedometer error.
3. If the possible tire/wheel assembly and/or driveline/transmission output shaft/rear axle pinion gear rotational speed related frequencies still DO NOT match the dominant frequency of the disturbance, the disturbance is most likely torque/load sensitive.
4. 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 driveline/transmission output shaft/rear axle pinion gear.

Scheme 28

AXLE SHAFTS

Begin the system diagnosis with VIBRATION DIAGNOSIS & CORRECTION and by reviewing AXLE SHAFTS under DESCRIPTION & OPERATION. Reviewing these sections will help you to determine if the condition described by the customer is normal operation. See AXLE SHAFTS under SYMPTOMS in order to identify the correct procedure for diagnosing the system and where the procedure is located.

FRONT DIFFERENTIAL ASSEMBLY

Begin the system diagnosis by reviewing the system FRONT DIFFERENTIAL ASSEMBLY under DESCRIPTION & OPERATION. Reviewing the description and operation information will help you determine the correct symptom diagnostic procedure when a malfunction exist. Reviewing the description and operation information will also help you determine if the condition described by the customer is normal operation. See FRONT DIFFERENTIAL ASSEMBLY under SYMPTOMS in order to identify the correct procedure for diagnosing the system and where the procedure is located.

Begin the system diagnosis with VIBRATION DIAGNOSIS & CORRECTION and by reviewing DRIVESHAFT under DESCRIPTION & OPERATION. Reviewing these sections will help you determine if the concern is related to the driveshaft. Reviewing the description and operation information will also help you determine if the condition described by the customer is normal operation. See DRIVESHAFT under SYMPTOMS in order to identify the correct procedure for diagnosing the system, where the procedure is located and in order to isolate and identify driveshaft related concerns.

REAR DIFFERENTIAL ASSEMBLY (STANDARD)

Begin the system diagnosis by reviewing the REAR AXLE DISASSEMBLED VIEWS in appropriate DRIVESHAFTS article DRIVELINE/AXLES. Also review REAR DIFFERENTIAL ASSEMBLY and AXLE SHAFTS under DESCRIPTION & OPERATION. Reviewing the description and operation information will help you determine the correct symptom diagnostic procedure when a malfunction exists. Reviewing the description and operation information will also help you determine if the condition described by the customer is normal operation. See REAR DIFFERENTIAL ASSEMBLY under SYMPTOMS in order to identify the correct procedure for diagnosing the system and where the procedure is located.

REAR DIFFERENTIAL ASSEMBLY (LOCKING/LIMITED SLIP)

Begin the system diagnosis by reviewing the system description and operation. See LOCKING DIFFERENTIAL and LIMITED SLIP DIFFERENTIAL under DESCRIPTION & OPERATION. Reviewing the description and operation information will help you determine the correct symptom diagnostic procedure when a malfunction exist. Reviewing the description and operation information will also help you determine if the condition described by the customer is normal operation. See REAR DIFFERENTIAL ASSEMBLY (LOCKING/LIMITED SLIP) under SYMPTOMS in order to identify the correct procedure for diagnosing the system and where the procedure is located.

Before beginning diagnosis, review the system description and operation in order to familiarize yourself with the system function. See AXLE SHAFTS under DESCRIPTION & OPERATION.

Classifying The Symptom

Axle Shaft symptoms can usually be classified into the following categories.

1. Leaks
2. Noises
3. Vibrations

For leak and noise related concerns, see

SYMPTOM LIST

. For additional information not addressed here, see TROUBLE SHOOTING in GENERAL INFORMATION. For vibration related symptoms, refer to

VIBRATION DIAGNOSIS & CORRECTION

under DIAGNOSTIC STARTING POINT.

Visual/Physical Inspection

1. Inspect the system for aftermarket devices which could affect the operation of the axle shafts.
2. Inspect the easily accessible or visible system components for obvious damage or conditions which could cause the symptom.

Symptom List

Refer to a symptom diagnostic procedure from the following list in order to diagnose the symptom

1. «CLICK NOISE IN TURNS»(/buick/century/vi-1997-2005/remont/axle-shafts/#vibration-drivetrain__click-noise-in-turns) under TROUBLE SHOOTING.
2. «CLUNK WHEN ACCELERATING FROM COAST»(/buick/century/vi-1997-2005/remont/axle-shafts/#vibration-drivetrain__clunk-when-accelerating-from-coast) under TROUBLE SHOOTING.
3. «CLUNK NOISE WHEN ACCELERATING DURING TURNS»(/buick/century/vi-1997-2005/remont/axle-shafts/#vibration-drivetrain__clunk-noise-when-accelerating-during-turns) under TROUBLE SHOOTING.
4. «SHUDDER ON ACCELERATION AT LOW SPEED»(/buick/century/vi-1997-2005/remont/axle-shafts/#vibration-drivetrain__shudder-on-acceleration-at-low-speed) under TROUBLE SHOOTING.

Before beginning diagnosis, review the system description and operation in order to familiarize yourself with the system functions. See FRONT DIFFERENTIAL ASSEMBLY under DESCRIPTION & OPERATION.

Noise Diagnosis

Any gear-driven unit produces a certain amount of noise that is normal and that conventional repairs or adjustment cannot eliminate. Slight noise that is heard only at a certain speed or under unusual or remote conditions is acceptable. For example, this noise tends to reach a peak at speeds from 40-60 MPH depending upon road and load conditions, or upon gear ratio and tire size. Noise of this kind does not indicate trouble in the axle assembly.

When an axle is suspected of being noisy, make a thorough test in order to determine whether the noise originates in the tires, road surface, wheel bearings, engine, transmission, driveshaft, or axle assembly.

Front differential assembly symptoms can usually be classified into the following categories

1. Leaks
2. Noises
3. Vibrations

For leak and noise related concerns, see

SYMPTOMS LIST

. For additional information not addressed here, see TROUBLE SHOOTING in GENERAL INFORMATION. For vibration related symptoms, refer to

VIBRATION DIAGNOSIS & CORRECTION

under DIAGNOSTIC STARTING POINT.

1. Inspect the system for loose or missing fasteners.
2. Inspect the system for loose or leaking components.
3. Inspect the system for obvious damage or conditions which may cause the symptom.

Symptoms List

Refer to a symptom diagnostic procedure from the following list in order to diagnose the symptom

1. See «FRONT DIFFERENTIAL ASSEMBLY NOISES»(/buick/century/vi-1997-2005/remont/axle-shafts/#vibration-drivetrain) .
2. See «NOISY IN DRIVE»(/buick/century/vi-1997-2005/remont/axle-shafts/#vibration-drivetrain) under TROUBLE SHOOTING.
3. See «NOISY WHEN COASTING»(/buick/century/vi-1997-2005/remont/axle-shafts/#vibration-drivetrain__noisy-when-coasting) under TROUBLE SHOOTING.
4. See «INTERMITTENT NOISE»(/buick/century/vi-1997-2005/remont/axle-shafts/#vibration-drivetrain) under TROUBLE SHOOTING.
5. See «CONSTANT NOISE»(/buick/century/vi-1997-2005/remont/axle-shafts/#vibration-drivetrain) under TROUBLE SHOOTING.
6. See «NOISY ON TURNS»(/buick/century/vi-1997-2005/remont/axle-shafts/#vibration-drivetrain) under TROUBLE SHOOTING.
7. See «FRONT DIFFERENTIAL ASSEMBLY LUBRICANT LEAK DIAGNOSIS»(/buick/century/vi-1997-2005/remont/axle-shafts/#vibration-drivetrain__front-differential-assembly-lubricant-leak-diagnosis) under TROUBLE SHOOTING.

Review the driveshaft system function. See DRIVESHAFT under Description & Operation.

Driveshaft symptoms can usually be classified into the following categories.

1. Leaks
2. Noises
3. Vibrations

For leak and noise related concerns, see

SYMPTOM LIST

. For additional information not addressed here, see TROUBLE SHOOTING under appropriate DRIVE AXLE article in BASIC TROUBLE SHOOTING in GENERAL INFORMATION. For vibration related symptoms, refer to

VIBRATION DIAGNOSIS & CORRECTION

under DIAGNOSTIC STARTING POINT.

1. Inspect for aftermarket devices, which could affect the operation of the vehicle. See «AFTERMARKET ADD-ON ACCESSORIES»(/buick/century/vi-1997-2005/remont/axle-shafts/#vibration-drivetrain__aftermarket-add-on-accessories) under VIBRATION DUPLICATED, COMPONENT NOT IDENTIFIED under VIBRATION DIAGNOSTIC AIDS.
2. Inspect the easily accessible or visible system components for obvious damage or conditions, which could cause the symptom.
3. Verify the exact operating conditions under which the concern exists. Note factors such as vehicle speed, road conditions, ambient temperature, and other specifics.
4. Compare driving characteristics or sounds, if applicable, to a known good vehicle and make sure you are not trying to correct a normal condition.

Intermittent

Text the vehicle under the same conditions that the customer reported in order to verify the system is operating properly.

Refer to a symptom diagnostic procedure from the following list in order to diagnose the symptom

1. See «RATTLE NOISE»(/buick/century/vi-1997-2005/remont/axle-shafts/#vibration-drivetrain__rattle-noise) under TROUBLE SHOOTING.
2. See «UNIVERSAL JOINT NOISE»(/buick/century/vi-1997-2005/remont/axle-shafts/#vibration-drivetrain) under TROUBLE SHOOTING.
3. See «PING, SNAP, OR CLICK NOISE»(/buick/century/vi-1997-2005/remont/axle-shafts/#vibration-drivetrain__ping-snap-or-click-noise) under TROUBLE SHOOTING.
4. See «KNOCK OR CLUNK NOISE»(/buick/century/vi-1997-2005/remont/axle-shafts/#vibration-drivetrain__knock-or-clunk-noise) under TROUBLE SHOOTING.
5. See «SCRAPING NOISE»(/buick/century/vi-1997-2005/remont/axle-shafts/#vibration-drivetrain__scraping-noise) under TROUBLE SHOOTING.
6. See «MOANING NOISE»(/buick/century/vi-1997-2005/remont/axle-shafts/#vibration-drivetrain__moaning-noise) under TROUBLE SHOOTING.
7. See «WHIRRING OR SQUEALING NOISE»(/buick/century/vi-1997-2005/remont/axle-shafts/#vibration-drivetrain__whirring-or-squealing-noise) under TROUBLE SHOOTING.
8. See «SQUEAK NOISE»(/buick/century/vi-1997-2005/remont/axle-shafts/#vibration-drivetrain__squeak-noise) under TROUBLE SHOOTING.
9. See «SHUDDER ON ACCELERATION AT LOW SPEED»(/buick/century/vi-1997-2005/remont/axle-shafts/#vibration-drivetrain__shudder-on-acceleration-at-low-speed) under TROUBLE SHOOTING.

Strategy Based Diagnostics

Review the system operations in order to familiarize yourself with the system functions. See REAR DIFFERENTIAL ASSEMBLY and AXLE SHAFTS under DESCRIPTION & OPERATION. All diagnosis on a vehicle should follow a logical process. Strategy based diagnostics is a uniform approach for repairing all systems. The diagnostic flow may always be used in order to resolve a system problem. The diagnostic flow is the place to start when repairs are necessary. For a detailed explanation, refer to Strategy Based Diagnosis in General Information.

1. Inspect for aftermarket devices, which could affect the operation of the vehicle.
2. Inspect the easily accessible or visible system components for obvious damage or conditions, which could cause the symptom.
3. Check for the correct lubricant level and the proper viscosity.
4. Verify the exact operating conditions under which the concern exists. Note factors such as vehicle speed, road conditions, ambient temperature, and other specifics.
5. Compare the driving characteristics or sounds, if applicable, to a known good vehicle and make sure you are not trying to correct a normal condition.

Intermittents

Test the vehicle under the same conditions that the customer reported in order to verify the system is operating properly.

Refer to a symptom diagnostic procedure from the following list in order to diagnose the symptom. For noise and leak related symptoms, see TROUBLE SHOOTING under appropriate DRIVE AXLE article in BASIC TROUBLE SHOOTING in GENERAL INFORMATION.

1. See «VIBRATION DIAGNOSIS & CORRECTION»(/buick/century/vi-1997-2005/remont/axle-shafts/#vibration-drivetrain__vibration-diagnosis-correction) under DIAGNOSTIC STARTING POINT.
2. See appropriate AUTOMATIC TRANSMISSION article in TRANSAXLE/TRANSMISSIONS.
3. See MANUAL TRANSMISSION NOISY (if equipped) under TROUBLE SHOOTING in appropriate MANUAL TRANSMISSIONS article in TRANSAXLE/TRANSMISSIONS.
4. See «DRIVESHAFT»(/buick/century/vi-1997-2005/remont/axle-shafts/#vibration-drivetrain) under SYMPTOMS.
5. See CLUTCH NOISY under TROUBLE SHOOTING in appropriate CLUTCH article in TRANSAXLE/TRANSMISSIONS.
6. See «REAR DIFFERENTIAL ASSEMBLY NOISES»(/buick/century/vi-1997-2005/remont/axle-shafts/#vibration-drivetrain) under TROUBLE SHOOTING.
7. See «NOISY IN DRIVE»(/buick/century/vi-1997-2005/remont/axle-shafts/#vibration-drivetrain) under TROUBLE SHOOTING.
8. See «NOISY WHEN COASTING»(/buick/century/vi-1997-2005/remont/axle-shafts/#vibration-drivetrain__noisy-when-coasting) under TROUBLE SHOOTING.
9. See «INTERMITTENT NOISE»(/buick/century/vi-1997-2005/remont/axle-shafts/#vibration-drivetrain) under TROUBLE SHOOTING.
10. See «CONSTANT NOISE»(/buick/century/vi-1997-2005/remont/axle-shafts/#vibration-drivetrain) under TROUBLE SHOOTING.
11. See «NOISY ON TURNS»(/buick/century/vi-1997-2005/remont/axle-shafts/#vibration-drivetrain) under TROUBLE SHOOTING.
12. See «REAR DIFFERENTIAL ASSEMBLY LUBRICANT LEAK DIAGNOSIS»(/buick/century/vi-1997-2005/remont/axle-shafts/#vibration-drivetrain__rear-differential-assembly-lubricant-leak-diagnosis) under TROUBLE SHOOTING.

Review the system and operation in order to familiarize yourself with the system functions. See LOCKING DIFFERENTIAL and LIMITED SLIP DIFFERENTIAL under DESCRIPTION & OPERATION.

1. Inspect the system for the following: Loose or missing fasteners. Obvious damage or conditions which may cause the symptom.
2. Check the system for proper operation. See «LOCKING DIFFERENTIAL DIAGNOSIS»(/buick/century/vi-1997-2005/remont/axle-shafts/#vibration-drivetrain__locking-differential-diagnosis) and «LIMITED SLIP DIFFERENTIAL DIAGNOSIS»(/buick/century/vi-1997-2005/remont/axle-shafts/#vibration-drivetrain__limited-slip-differential-diagnosis) under TROUBLE SHOOTING.

Refer to a system diagnostic procedure from the following list in order to diagnose the symptom

1. See «LOCKING REAR AXLE DOES NOT LOCK»(/buick/century/vi-1997-2005/remont/axle-shafts/#vibration-drivetrain) under TROUBLE SHOOTING.
2. See «LOCKING REAR AXLE LOCKS IN TURNS»(/buick/century/vi-1997-2005/remont/axle-shafts/#vibration-drivetrain) under TROUBLE SHOOTING.
3. See «LIMITED SLIP DIFFERENTIAL CHATTERS IN TURNS»(/buick/century/vi-1997-2005/remont/axle-shafts/#vibration-drivetrain) under TROUBLE SHOOTING.
4. See «LOCKING REAR DRIVE AXLE CHATTERS IN TURNS»(/buick/century/vi-1997-2005/remont/axle-shafts/#vibration-drivetrain) under TROUBLE SHOOTING.
5. See «NOISE IN ADDITION TO NORMAL CLUTCH ENGAGEMENT»(/buick/century/vi-1997-2005/remont/axle-shafts/#vibration-drivetrain__noise-in-addition-to-normal-clutch) under TROUBLE SHOOTING.

VIBRATION DIAGNOSTIC AIDS

Note. If you have not reviewed the Diagnostic Starting Point - Vibration Diagnosis and completed the Vibration Analysis tables as indicated, refer to VIBRATION DIAGNOSIS & CORRECTION under DIAGNOSTIC STARTING POINT before proceeding.

The diagnostic information contained in this Diagnostic Aids section will help you determine the correct course of action to take for the following 4 main conditions. Refer to the appropriate condition from this list.

1. «VIBRATION INTERMITTENT OR NOT DUPLICATED»(/buick/century/vi-1997-2005/remont/axle-shafts/#vibration-drivetrain__vibration-intermittent-or-not-duplicated)
2. «VIBRATION DUPLICATED, COMPONENT NOT IDENTIFIED»(/buick/century/vi-1997-2005/remont/axle-shafts/#vibration-drivetrain__vibration-duplicated-component-not-identified)
3. «VIBRATION DUPLICATED, DIFFICULT TO ISOLATE/BALANCE COMPONENT»(/buick/century/vi-1997-2005/remont/axle-shafts/#vibration-drivetrain__vibration-duplicated-difficult-to-isolatebalance-component)
4. «VIBRATION DUPLICATED, APPEARS TO BE POTENTIAL OPERATING CHARACTERISTIC»(/buick/century/vi-1997-2005/remont/axle-shafts/#vibration-drivetrain__vibration-duplicated-appears-to-be-potential)

VIBRATION INTERMITTENT OR NOT DUPLICATED

Note. 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.

Temperature, Ground-Out, Accessory Load

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 1-2" (2.5-5 cm) 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. An improper power steering fluid level could produce noises in the power steering system. An improper air conditioning refrigerant level or an excessive amount of refrigerant oil could produce noises or possibly vibrations in the air conditioning system.
7. 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 DUPLICATED, COMPONENT NOT IDENTIFIED

Note. If you have not completed the Vibration Analysis tables as indicated and reviewed Vibration Diagnostic Aids, refer to VIBRATION DIAGNOSTIC AIDS before proceeding.

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.

Aftermarket Add-On Accessories

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 and isolated properly, the transfer path would be removed and the disturbance would no longer be present.

VIBRATION DUPLICATED, DIFFICULT TO ISOLATE/BALANCE COMPONENT

Note. 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 duplicated the vibration concern but have had difficulty in balancing a component or isolating a component, refer to the following information.

Most vibration concerns are corrected or eliminated through correcting excessive runout of a component, correcting balance of a component or isolating a component which has come into abnormal contact with another object/component.

Components which can generate a lot of energy and are experiencing excessive runout, imbalance or ground-out can produce a vibration with a strong enough amplitude that the vibration can transmit to components which are closely related. This type of a condition is usually related to and sensitive to torque-load. The most likely system that could exhibit this type of a condition is the driveline.

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 driveshaft(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 driveshaft 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 driveshaft is attached should be suspected to have internal problems which are being transmitted to the driveshaft. See FRONT DIFFERENTIAL ASSEMBLY under DIAGNOSTIC STARTING POINT, or REAR DIFFERENTIAL ASSEMBLY under TROUBLE SHOOTING in appropriate DRIVELINE/AXLES article, for internal axle diagnostics.

VIBRATION DUPLICATED, APPEARS TO BE POTENTIAL OPERATING CHARACTERISTIC

Note. If you have not completed the Vibration Analysis tables as indicated and reviewed Vibration Diagnostic Aids, refer to VIBRATION DIAGNOSTIC AIDS before proceeding.

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 «VIBRATION DIAGNOSIS & CORRECTION»(/buick/century/vi-1997-2005/remont/axle-shafts/#vibration-drivetrain__vibration-diagnosis-correction) under DIAGNOSTIC STARTING POINT 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.

VIBRATION ANALYSIS - ROAD TESTING

Note. For Vibration Analysis - Road Testing, refer to illustrations. (Scheme 29)- (Scheme 32).

Scheme 29

Scheme 30

Scheme 31

Scheme 32

CLICK NOISE IN TURNS

1. Check for worn or damaged outer CV joints. Are the outer CV joints/seals worn? If so, go to next step. If not, system is okay.
2. Replace the outer CV joints/seals. See AXLE SHAFT OUTER JOINT & SEAL under REMOVAL & INSTALLATION in appropriate AXLE SHAFTS article in DRIVELINE/AXLES. Is the repair complete? If so, system is okay.

CLUNK WHEN ACCELERATING FROM COAST

1. Check for a loose axle shaft to hub assembly nut. Is the axle shaft nut loose? If so, go to next step. If not, go to step 3 .
2. Tighten the axle shaft to hub assembly nut to appropriate specification. Is the repair complete? If so, system is okay.
3. Check for a damaged inner CV joint. Is the inner CV joint damaged? If so, go to next step. If not, system is okay.
4. Replace the inner CV joint. See AXLE SHAFT INNER JOINT & SEAL under REMOVAL & INSTALLATION in appropriate AXLE SHAFTS article in DRIVELINE/AXLES. Is the repair complete? If so, system is okay.

CLUNK NOISE WHEN ACCELERATING DURING TURNS

1. Check for worn or damaged outer CV joints and/or seals. Are the outer CV joints/seals worn? If so, go to next step. If not, system is okay.
2. Replace the outer CV joints/seals. See AXLE SHAFT OUTER JOINT & SEAL under REMOVAL & INSTALLATION in appropriate AXLE SHAFTS article in DRIVELINE/AXLES. Is the repair complete? If so, system is okay.

Gear Noise

Gear noise or whine is audible from 20-55 MPH under 4 driving conditions

1. Drive - Acceleration or heavy pull.
2. Road Load - Vehicle driving load or constant speed.
3. Float - Using enough throttle to keep the vehicle from driving the engine, the vehicle slows down gradually but the engine still pulls slightly.
4. Coast - Throttle is closed and the vehicle is in gear.

Gear noise most frequently has periods where the noise is more prominent, usually between 30-40 MPH and 50-53 MPH. Gear whine is corrected by ring and pinion gear replacement or adjustment, depending on the mileage of the gear set.

Bearing Noise

Faulty bearings produce a rough growl or grating sound, rather than the whine typical of gear noise. Bearing noise (hum) will pulsate at a constant vehicle speed. This indicates a bad pinion or a bad front axle side bearing. This noise can be confused with front wheel bearing noise. Inspect and replace the bearings and the affected components as required.

Front Wheel Bearing Noise

A rough front wheel bearing produces a noise which continues with the vehicle coasting at low speed and the transmission in neutral. The noise may diminish some when the brakes are gently applied. The noise may also change when performing side-to-side maneuvers with the vehicle.

A rough and/or noisy wheel bearing can be heard by spinning the wheels by hand and listening at the hubs for the noise. Inspect and replace the bearings and the affected components as needed.

Knock At Low Speeds

A low speed knock can be caused by a differential case side gear bore that has worn oversize. Inspect the side gears and the differential case assembly and replace the components as necessary.

Backlash Clunk

Excessive backlash clunk under acceleration or de-acceleration can be caused by any of the following

1. Worn differential pinion shaft.
2. Worn differential pinion and/or side gear teeth.
3. Worn thrust washers.
4. Excessive clearance between the side gears and the axle shafts.
5. Excessive clearance between differential side gears and the bore in the case.
6. Excessive drive pinon and ring gear backlash.

Inspect, adjust or replace the affected components as necessary.

Gear noise or whine is audible from 20-55 MPH under 4 driving conditions

1. Drive - Acceleration or heavy pull.
2. Road Load - vehicle driving load or constant speed.
3. Float - Using enough throttle to keep the vehicle from driving the engine, the vehicle slows down gradually but the engine still pulls slightly.
4. Coast - Throttle is closed and the vehicle is in gear.

Gear noise most frequently has periods where the noise is more prominent, usually between 30-40 MPH and 50-53 MPH. Gear whine is corrected by either ring and pinion gear replacement or adjustment, depending on the mileage of the gearset.

Faulty bearings produce a rough growl or grating sound, rather than the whine typical of gear noise. Bearing noise (hum) will pulsate at a constant vehicle speed. This indicates a bad pinion or a bad front axle side bearing. This noise can be confused with front wheel bearing noise. Inspect and replace the bearings and the affected components as required.

Rear Wheel Bearing Noise

A rough rear wheel bearing produces a noise which continues with the vehicle coasting at low speed and the transmission in neutral. The noise may diminish some when the brakes are gently applied. The noise may also change when performing side-to-side maneuvers with the vehicle.

A rough/noisy rear wheel bearing can be heard by spinning the rear wheels by hand and listening at the hubs for the noise. Inspect and replace the bearings and the affected components as needed.

A low speed knock can be caused by a differential case side gear bore that has worn oversize. Inspect the side gears and differential case and replace the components as necessary.

Excessive backlash clunk under acceleration or deceleration can be caused by any of the following

1. Worn differential pinion shaft.
2. Worn differential pinion and/or side gear teeth.
3. Worn thrust washers.
4. Excessive clearance between the side gears and the axle shafts.
5. Excessive clearance between differential side gears and the bore in the case.
6. Excessive drive pinon and ring gear backlash.

Inspect, adjust or replace the affected components as necessary.

Excessive Pinion To Ring Gear Backlash

Adjust the pinion to ring gear backlash. See BACKLASH INSPECTION & ADJUSTMENT under OVERHAUL in appropriate DIFFERENTIALS article in DRIVELINE/AXLES.

Worn Pinion & Ring Gear

Replace the pinion and ring gear. See PINION AND RING GEAR under OVERHAUL in appropriate DIFFERENTIALS article in DRIVELINE/AXLES.

Worn Pinion Bearings

Replace the pinion bearings. See PINION & RING GEAR under OVERHAUL in appropriate DIFFERENTIALS article in DRIVELINE/AXLES.

Loose Pinion Bearings

Adjust the pinion bearings preload. See PINION BEARINGS PRELOAD under OVERHAUL in appropriate DIFFERENTIALS article in DRIVELINE/AXLES.

Excessive Pinion End Play

Adjust the pinion end play. See PINION END PLAY ADJUSTMENT under OVERHAUL in appropriate DIFFERENTIALS article in DRIVELINE/AXLES.

Worn Differential Bearings

Replace the differential bearings. See DIFFERENTIAL BEARINGS under OVERHAUL in appropriate DIFFERENTIALS article in DRIVELINE/AXLES.

Loose Differential Bearings

Adjust the differential bearing preload. See DIFFERENTIAL BEARING PRELOAD under OVERHAUL in appropriate DIFFERENTIALS article in DRIVELINE/AXLES.

Excessive Ring Gear Runout

Replace the ring gear. See RING GEAR under OVERHAUL in appropriate DIFFERENTIALS article in DRIVELINE/AXLES.

Low Oil Level

Fill the fluid level to specifications with the proper lubricant.

Wrong Or Poor Grade Oil

Drain and refill the system with the proper lubricant.

NOISY WHEN COASTING

Note. Noise is audible when slowing down and disappears when driving.

Adjust or replace the pinion and the ring gear. See PINION AND RING GEAR under OVERHAUL in appropriate DIFFERENTIALS article in DRIVELINE/AXLES.

Pinion & Ring Gear Too Tight

Adjust the pinion and the ring gear backlash. See BACKLASH INSPECTION & ADJUSTMENT under OVERHAUL in appropriate DIFFERENTIALS article in DRIVELINE/AXLES.

Warped Ring Gear

Replace the ring gear. See RING GEAR under OVERHAUL in appropriate DIFFERENTIALS article in DRIVELINE/AXLES.

Loose Differential Case Assembly

Set the differential case assembly to the proper preload and backlash. See BACKLASH INSPECTION & ADJUSTMENT under OVERHAUL in appropriate DIFFERENTIALS article.

Flat Spot On The Pinion Or The Ring Gear Teeth

Replace the pinion and the ring gear. See PINION AND RING GEAR under OVERHAUL in appropriate DIFFERENTIALS article in DRIVELINE/AXLES.

Flat Spot On The Pinion Bearing

Replace the bearing. See PINION BEARING under OVERHAUL in appropriate DIFFERENTIALS article in DRIVELINE/AXLES.

Worn Pinion Splines

Replace the pinion. See PINION under OVERHAUL in appropriate DIFFERENTIALS article in DRIVELINE/AXLES.

Worn Differential Side Gears & Pinions

Replace the differential side gears and pinions. See DIFFERENTIAL SIDE GEARS & PINIONS under OVERHAUL in appropriate DIFFERENTIALS article in DRIVELINE/AXLES.

Worn Differential Spider

Replace the spine gears. See SPINE GEARS under OVERHAUL in appropriate DIFFERENTIALS article in DRIVELINE/AXLES.

Worn Axle Shaft Splines

Replace the axle shaft. See AXLE SHAFTS under OVERHAUL in appropriate DIFFERENTIALS article in DRIVELINE/AXLES.

FRONT DIFFERENTIAL ASSEMBLY LUBRICANT LEAK DIAGNOSIS

Front axle lubricant leaks can occur at the following locations

1. Axle shaft oil seals.
2. Differential carrier assembly mating surface.
3. Drain plug.
4. Fill plug.
5. Inner axle tube assembly to differential carrier assembly mating surface.
6. Pinion yoke oil seal.
7. Vent tube.

Determining The Cause

While most front axle leaks may be easy to find, determining the cause may not be. A thorough inspection of the area around the leak may assist in determining the cause of the leak.

Oil Seals - Lubricant leaks from a oil seal may be caused by any of the following

1. An improperly installed seal.
2. A distorted seal.
3. A worn seal.
4. A worn shaft.
5. A brittle seal lip.
6. A hardened seal lip.

To determine the actual cause of the leak, clean the area around the leak. Observe the area of the leak and determine the if the seal or another component is causing the leak. A worn seal surface will cause a leak at the sealing lip while a misaligned seal or a seal installed into a housing with an excessive bore will cause the seal to leak at the outside surface of the seal. Hardened or cracked seal lips usually indicate the axle is operating beyond the normal temperature limits for the axle. A seal whose sealing surface has been nicked or cut may indicate that the shaft has a rough, burred, or gouged surface and will need to be inspected before the seal can be replaced.

Sealing Surfaces

Front axles components are assembled using specific sealers. A leak at a surface sealed with sealant is usually caused by a poor fit of the components but can also be caused by the use of the wrong sealant. When correcting a sealant leak, inspect each component for distortion and for nicks or gouges that may prohibit the sealant from sealing properly and when reassembling the component, use the proper sealant.

Differential Carrier Assembly - Lubricant leaks at the differential carrier assembly can occur at the following locations

1. Drain plug.
2. Fill plug.
3. Vent tube.

Drain and fill plug leaks are usually caused by a loose plug. A vent tube leak can be cause by a loose fitting vent hose or by a vent tube assembly whose interior shield is stuck in the upside down position. Inspect the vent plug's interior shield for unrestricted movement, repair or replace the plug as necessary. Drain or fill plug leaks can be repaired by either tightening the plug or by using an approved sealer on the threads on the plug.

REAR DIFFERENTIAL ASSEMBLY LUBRICANT LEAK DIAGNOSIS

Rear axle lubricant leaks can occur at the following locations

1. Axle Tube To Differential Carrier Housing Joint
2. Axle Shaft Oil Seal
3. Axle Housing Porosity
4. Differential Housing Cover Gasket
5. Drain Plug
6. Fill Plug
7. Pinion Yoke Oil Seal
8. Vent Tube

While most rear axle leaks may be easy to find, determining the cause may not be. A thorough inspection of the area around the leak may assist in determining the cause of the leak.

Oil Seals - Lubricant leaks from a oil seal may be caused by any of the following

1. An improperly installed seal.
2. A distorted seal.
3. A worn seal.
4. A worn shaft.
5. A brittle seal lip.
6. A hardened seal lip.

To determine the actual cause of the leak, clean the area around the leak. Observe the area of the leak and determine the if the seal or another component is causing the leak. A worn seal surface will cause a leak at the sealing lip while a misaligned seal or a seal installed into a housing with an excessive bore will cause the seal to leak at the outside surface of the seal. Hardened or cracked seal lips usually indicate the axle is operating beyond the normal temperature limits for the axle. A seal whose sealing surface has been nicked or cut may indicate that the shaft has a rough, burred, or gouged surface and will need to be inspected before the seal can be replaced.

Gaskets - A leak at a gasket is usually caused by a poor fit of the components on each side of the gasket surface. Inspect each component for distortion and for nicks or gouges that may prohibit the gasket from sealing properly.

Rear Axle Housing - Rear axle housing lubricant leaks usually occur at the following locations

1. Drain Plug.
2. Fill Plug.

Drain and fill plug leaks are usually caused by a loose plug. These leaks can by repaired by either tightening the plug or by using an approved sealer on the threads on the plug. Other leaks such as axle tube to differential carrier housing or porosity leaks require the replacement of the rear axle housing.

LOCKING DIFFERENTIAL DIAGNOSIS

1. Place the vehicle on a frame-contact hoist, allowing free rotation of the rear wheels.
2. Hold one wheel stationary. Slowly rotate the other wheel approximately 1/2 revolution per second in both the forward and reversed directions. The wheel should rotate freely. The differential is locking and is broken if both wheels attempt to turn together.
3. Raise the hoist to maximum height with one person in the vehicle.
4. Start the engine. Ensure that the engine is operating at low idle speed (warm engine).
5. Apply the service brake. Place the automatic transmission in drive. Depress the clutch and place the transmission in first gear with a manual transmission.
6. Lock one rear wheel by pulling one parking brake cable from under the vehicle with the aid of an assistant.
7. Release the service brakes or disengage the clutch slowly enough to start the free wheel turning. The locked rear wheel remains stationary.
8. Increase the speed of the free wheel. The differential will lock, causing the rotating wheel to stop or both wheels to turn at the same speed. The engine, if equipped with manual transmission, may stall. In order to cause the differential to lock, you may need to accelerate the engine until approximately 10 MPH is indicated on the vehicle speedometer. If the indicated speed can be increased beyond 20 MPH without causing the differential to lock, the unit is not functioning properly. Rapid release of the brakes or clutch, or rapid acceleration of the engine, will invalidate the test.
9. Lock the opposite rear wheel and repeat the procedure.

LIMITED SLIP DIFFERENTIAL DIAGNOSIS

1. Did you review the general description and perform the necessary inspections? If so, go to next step. If not, see «LOCKING/LIMITED SLIP REAR DIFFERENTIAL»(/buick/century/vi-1997-2005/remont/axle-shafts/#vibration-drivetrain__rear-differential-assembly-lockinglimited-slip) under DIAGNOSTIC STARTING POINT.
2. Measure the rotational force of the axle using the following procedure: Block the front wheels. Raise and support the vehicle. Remove the tire and wheel. Using the Front/Rear Spindle Remover (J-28733-B), measure the rotational force of the axle. See «AXLE ROTATIONAL FORCE SPECIFICATION»(/buick/century/vi-1997-2005/remont/axle-shafts/#vibration-drivetrain) . Repeat the procedure for the other axle. Does the force measure outside the specified range? If so, go to next step. If not, system is okay.
3. Repair the rear axle. Did you complete the repair? If so, go to next step.
4. Operate the system in order to verify the repair. Did you correct the condition? If so, system is okay. If not, go to step 2 .

AXLE ROTATIONAL FORCE SPECIFICATION

LEAK AT FRONT SLIP YOKE

Note. An occasional drop of lubricant leaking from the splined yoke is normal and requires no attention.

The Slip Yoke Barrel Is Burred, Nicked, Corroded, Or Worn

Inspect the slip yoke for burrs. Minor burrs can be removed by careful use of crocus cloth or fine stone honing. If the is badly burred, corroded or worn, replace the yoke. See SLIP YOKE under REMOVAL & INSTALLATION in appropriate DIFFERENTIALS article in DRIVELINE/AXLES.

Replace the oil seal. See OUTPUT SHAFT SEAL under REMOVAL & INSTALLATION in appropriate DIFFERENTIALS article in DRIVELINE/AXLES.

There Is A Faulty Transmission Or Transfer Case Output Shaft Oil Seal

Replace the oil seal. See OUTPUT SHAFT SEAL under REMOVAL & INSTALLATION in appropriate DIFFERENTIALS article in DRIVELINE/AXLES.

One Or More Universal Joints Are Worn, Damaged Or Have Lost Lubrication

Replace "U" joints as necessary. See UNIVERSAL JOINT under REMOVAL & INSTALLATION in appropriate DRIVESHAFT & UNIVERSAL JOINTS article in DRIVELINE/AXLES.

The "U" Joint Hardware Has Become Loose

Tighten "U" joint hardware to appropriate specification.

PING, SNAP, OR CLICK NOISE

Note. A "ping, snap or click" is usually heard on initial load after the transmission is in gear, either in forward or reverse.

The Fixed Yoke Or The Pinion Yoke Is Loose

Tighten the bolts and the pinion nut to appropriate specification.

One Or More Of The Universal Joints Are Worn Or Damaged

Replace "U" joints as necessary. See UNIVERSAL JOINT under REMOVAL & INSTALLATION in appropriate DRIVESHAFT & UNIVERSAL JOINTS article in DRIVELINE/AXLES.

KNOCK OR CLUNK NOISE

Note. A "knocking or clunking" noise occurs when operating the vehicle in high gear or coasting in neutral at 10 MPH.

Replace "U" joints as necessary. See UNIVERSAL JOINT under REMOVAL & INSTALLATION in appropriate DRIVESHAFT & UNIVERSAL JOINTS article in DRIVELINE/AXLES.

The Side Gear Hub Counterbore In The Differential Is Worn Oversize

Replace the differential case and/or the side gears. See DIFFERENTIAL CASE and/or SIDE GEARS under OVERHAUL in DIFFERENTIALS & DRIVE AXLES.

SCRAPING NOISE

A "scraping" type noise may occur when something is rubbing against the rotating components of the driveline. Inspect entire driveline for wear marks or interference with any vehicle components. Correct the interference as necessary.

SQUEAK NOISE

Note. When driving the vehicle at various speeds a squeaking sound occurs. Refer to appropriate diagnosis to determine correct course of action.

One Or More Of The Universal Joints Have Lost Lubricant

Replace the universal joint. See UNIVERSAL JOINT under REMOVAL & INSTALLATION in appropriate DRIVESHAFT & UNIVERSAL JOINTS article in DRIVELINE/AXLES.

A Broken Or Missing Snap Ring On The Rear Bearing Housing Assembly (Manual Transmission Only)

A broken or missing snap ring on the rear bearing housing may allow the driveshaft assembly to move forward in the driveline tube. In those situations, the shoulder of the input shaft will contact the outer race of the clutch pilot bearing and create a "squealing or squeaking" type noise with the clutch pedal depressed.

SHUDDER ON ACCELERATION AT LOW SPEED

A driveshaft "out-of-balance" condition may create a vibration and be caused by

1. Bent driveshaft.
2. Loose or missing weights or parts.

Replace or balance components as required.

WHIRRING OR SQUEALING NOISE

A "whirring or squealing" type noise will increase or decrease relative to the vehicle speed and may be caused by a worn bearing within the driveline assembly. A minor "whirring" type noise should be considered normal. Replace the bearings as required.

MOANING NOISE

A rev limiter/snubber that is contacting the driveline tube may create a "moaning" type noise and/or vibration that is felt through the shift lever (manual transmission applications only). A rev limiter/snubber that is contacting the driveline tube may create a "moaning" type noise and/or vibration that is felt through the shift lever. Replace components as required.

RATTLE NOISE

A loose driveshaft hub clamp bolt may create a "rattle" type noise mainly at idle in the flywheel area of the transmission housing (automatic transmission applications only). Tighten driveshaft hub clamp bolt to appropriate specification.

Little Or No Preload On The Latching Bracket

Replace the governor assembly and the latching bracket.

Flyweights In The Governor Assembly Are Stuck Closed

Replace the governor assembly and the latching bracket.

Drive Teeth On The Governor Or Cam Gear Assembly Are Broken

Replace the cam plate, the governor assembly, and the latching bracket. Refer to the following

1. Locking differential disassemble. See OVERHAUL in appropriate DIFFERENTIALS article in DRIVELINE/AXLES.
2. Locking differential cam unit disassemble. See OVERHAUL in appropriate DIFFERENTIALS article in DRIVELINE/AXLES.
3. Locking differential cleaning and inspection. See OVERHAUL in appropriate DIFFERENTIALS article in DRIVELINE/AXLES.
4. Locking differential cam unit assemble. See OVERHAUL in appropriate DIFFERENTIALS article in DRIVELINE/AXLES.
5. Locking differential adjustment. See OVERHAUL in appropriate DIFFERENTIALS article in DRIVELINE/AXLES.
6. Locking differential assemble. See OVERHAUL in appropriate DIFFERENTIALS article in DRIVELINE/AXLES.

Broken Clutch Plates

Replace the clutch plates and the wave spring. Refer to the following

1. Locking differential disassemble. See OVERHAUL in appropriate DIFFERENTIALS article in DRIVELINE/AXLES.
2. Locking differential cam unit disassemble. See OVERHAUL in appropriate DIFFERENTIALS article in DRIVELINE/AXLES.
3. Locking differential cleaning and inspection. See OVERHAUL in appropriate DIFFERENTIALS article in DRIVELINE/AXLES.
4. Locking differential cam unit assemble. See OVERHAUL in appropriate DIFFERENTIALS article in DRIVELINE/AXLES.
5. Locking differential adjustment. See OVERHAUL in appropriate DIFFERENTIALS article in DRIVELINE/AXLES.
6. Locking differential assemble. See OVERHAUL in appropriate DIFFERENTIALS article in DRIVELINE/AXLES.

Governor Assembly Is Tight In Case

Free up the governor assembly. See OVERHAUL in appropriate DIFFERENTIALS article in DRIVELINE/AXLES.

Broken Or Weak Governor Flyweight Spring

Replace the governor assembly and the latching bracket. See OVERHAUL in appropriate DIFFERENTIALS article in DRIVELINE/AXLES.

Flyweight In Governor Assembly Is Stuck Open

Replace the governor assembly and the latching bracket. See OVERHAUL in appropriate DIFFERENTIALS article in DRIVELINE/AXLES.

Cam Plate Or Governor Drive Teeth Are Broken

Replace the cam plate, the governor assembly, and the latching bracket. Refer to the following

1. Locking differential disassemble. See OVERHAUL in appropriate DIFFERENTIALS article in DRIVELINE/AXLES.
2. Locking differential cam unit disassemble. See OVERHAUL in appropriate DIFFERENTIALS article in DRIVELINE/AXLES.
3. Locking differential cleaning and inspection. See OVERHAUL in appropriate DIFFERENTIALS article in DRIVELINE/AXLES.
4. Locking differential cam unit assemble. See OVERHAUL in appropriate DIFFERENTIALS article in DRIVELINE/AXLES.
5. Locking differential adjustment. See OVERHAUL in appropriate DIFFERENTIALS article in DRIVELINE/AXLES.
6. Locking differential assemble. See OVERHAUL in appropriate DIFFERENTIALS article in DRIVELINE/AXLES.

Lubricant Is Contaminated

Drain and flush the axle housing thoroughly. See OVERHAUL in appropriate DIFFERENTIALS article in DRIVELINE/AXLES. Refill with the correct lubricant.

Clutch Plates Are Deteriorated

Replace the clutch plates. See OVERHAUL in appropriate DIFFERENTIALS article in DRIVELINE/AXLES.

Drain and flush the axle housing thoroughly. See OVERHAUL in appropriate DIFFERENTIALS article in DRIVELINE/AXLES. Refill with the correct lubricant.

Replace the clutch plates. See OVERHAUL in appropriate DIFFERENTIALS article in DRIVELINE/AXLES.

NOISE IN ADDITION TO NORMAL CLUTCH ENGAGEMENT

Note. Refer to appropriate diagnosis to determine correct course of action.

Clutch Plates Are Broken

Replace the clutch plates. Refer to the following

1. Locking differential disassemble. See OVERHAUL in appropriate DIFFERENTIALS article in DRIVELINE/AXLES.
2. Locking differential cam unit disassemble. See OVERHAUL in appropriate DIFFERENTIALS article in DRIVELINE/AXLES.
3. Locking differential cleaning and inspection. See OVERHAUL in appropriate DIFFERENTIALS article in DRIVELINE/AXLES.
4. Locking differential cam unit assemble. See OVERHAUL in appropriate DIFFERENTIALS article in DRIVELINE/AXLES.
5. Locking differential adjustment. See OVERHAUL in appropriate DIFFERENTIALS article in DRIVELINE/AXLES.
6. Locking differential assemble. See OVERHAUL in appropriate DIFFERENTIALS article in DRIVELINE/AXLES.

Thrust Block Is Broken

Replace the thrust block with a block of identical thickness. Check closely for other damage. See LOCKING DIFFERENTIAL DISASSEMBLE and LOCKING DIFFERENTIAL ASSEMBLE in appropriate OVERHAUL article.

Case Is Damaged

Replace the unit. Refer to DIFFERENTIAL REPLACEMENT in appropriate REMOVAL & INSTALLATION article in DRIVELINE/AXLES.

Differential Gears Are Broken

Replace the gears. Refer to the following

1. Locking differential disassemble. See OVERHAUL in appropriate DIFFERENTIALS article in DRIVELINE/AXLES.
2. Locking differential cam unit disassemble. See OVERHAUL in appropriate DIFFERENTIALS article in DRIVELINE/AXLES.
3. Locking differential cleaning and inspection. See OVERHAUL in appropriate DIFFERENTIALS article in DRIVELINE/AXLES.
4. Locking differential cam unit assemble. See OVERHAUL in appropriate DIFFERENTIALS article in DRIVELINE/AXLES.
5. Locking differential adjustment. See OVERHAUL in appropriate DIFFERENTIALS article in DRIVELINE/AXLES.
6. Locking differential assemble. See OVERHAUL in appropriate DIFFERENTIALS article in DRIVELINE/AXLES.

See also:
• ELECTRONIC VIBRATION ANALYZER (EVA)
• VIBRATION ANALYSIS - ROAD TESTING
• VIBRATION THEORY & TERMINOLOGY
• VIBRATION DIAGNOSTIC AIDS
• VIBRATION DIAGNOSIS & CORRECTION
• AXLE SHAFTS
• FRONT DIFFERENTIAL ASSEMBLY
• DRIVESHAFT
• LOCKING DIFFERENTIAL
• LIMITED SLIP DIFFERENTIAL
• SYMPTOM LIST
• CLICK NOISE IN TURNS
• CLUNK WHEN ACCELERATING FROM COAST
• CLUNK NOISE WHEN ACCELERATING DURING TURNS
• SHUDDER ON ACCELERATION AT LOW SPEED
• SYMPTOMS LIST
• NOISY WHEN COASTING
• FRONT DIFFERENTIAL ASSEMBLY LUBRICANT LEAK DIAGNOSIS
• AFTERMARKET ADD-ON ACCESSORIES
• RATTLE NOISE
• PING, SNAP, OR CLICK NOISE
• KNOCK OR CLUNK NOISE
• SCRAPING NOISE
• MOANING NOISE
• WHIRRING OR SQUEALING NOISE
• SQUEAK NOISE
• REAR DIFFERENTIAL ASSEMBLY LUBRICANT LEAK DIAGNOSIS
• LOCKING DIFFERENTIAL DIAGNOSIS
• LIMITED SLIP DIFFERENTIAL DIAGNOSIS
• NOISE IN ADDITION TO NORMAL CLUTCH ENGAGEMENT
• VIBRATION INTERMITTENT OR NOT DUPLICATED
• VIBRATION DUPLICATED, COMPONENT NOT IDENTIFIED
• VIBRATION DUPLICATED, DIFFICULT TO ISOLATE/BALANCE COMPONENT
• VIBRATION DUPLICATED, APPEARS TO BE POTENTIAL OPERATING CHARACTERISTIC
• LOCKING/LIMITED SLIP REAR DIFFERENTIAL