Front Axle - 275FBI: Other — Front Axle - 275FBI — Differentials & Drive Axles

LOW SPEED KNOCK

Low speed knock is generally caused by

Worn U-joint(s).
Worn side-gear thrust washers.
Worn pinion shaft bore.

DRIVELINE SNAP

A snap or clunk noise when the vehicle is shifted into gear (or the clutch engaged) can be caused by

High engine idle speed.
Transmission shift operation.
Loose engine/transmission/transfer case mounts.
Worn U-joints.
Loose spring mounts.
Loose pinion gear nut and flange.
Excessive ring gear backlash.
Excessive side gear to case clearance.

The source of a snap or a clunk noise can be determined with the assistance of a helper. Raise the vehicle on a hoist with the wheels free to rotate. Instruct the helper to shift the transmission into gear and listen for the noise. A mechanics stethoscope is helpful in isolating the source of a noise.

Condition	Possible Causes	Correction
Wheel Noise	1. Wheel loose.	1. Tighten loose nuts.
Wheel Noise	2. Worn wheel bearing.	2. Replace bearing.
Axle Shaft Noise	1. Misaligned axle tube.	1. Inspect axle tube alignment. Correct as necessary.
	2. Bent or sprung axle shaft.	2. Inspect and correct as necessary.
	3. End-play in pinion bearings.	3. Refer to pinion preload information and correct as necessary.
	4. Excessive gear backlash between the ring gear and pinion.	4. Check adjustment of the ring gear and pinion backlash. Correct as necessary.
	5. Improper adjustment of pinion gear bearings.	5. Adjust the pinion bearings preload.
	6. Loose pinion flange nut.	6. Tighten the pinion flange nut.
	7. Scuffed gear tooth contact surfaces.	7. Inspect and replace as necessary.
Axle Shaft Broke	1. Misaligned axle tube.	1. Replace the broken shaft after correcting tube mis-alignment.
	2 Vehicle overloaded.	2. Replace broken shaft and avoid excessive weight on vehicle.
	3. Erratic clutch operation.	3. Replace broken shaft and avoid or correct erratic clutch operation.
	4. Grabbing clutch.	4. Replace broken shaft and inspect and repair clutch as necessary.
Differential Cracked	1. Improper adjustment of the differential bearings.	1. Replace case and inspect gears and bearings for further damage. Set differential bearing preload properly.
	2. Excessive ring gear backlash.	2. Replace case and inspect gears and bearings for further damage. Set ring gear backlash properly.
	3. Vehicle overloaded.	3. Replace case and inspect gears and bearings for further damage. Avoid excessive vehicle weight.
	4. Erratic clutch operation.	4. Replace case and inspect gears and bearings for further damage. Avoid erratic use of clutch.
Differential Gears Scored	1. Insufficient lubrication.	1. Replace scored gears. Fill differential with the correct fluid type and quantity.
	2. Improper grade of lubricant.	2. Replace scored gears. Fill differential with the correct fluid type and quantity.
	3. Excessive spinning of one wheel/tire.	3. Replace scored gears. Inspect all gears, pinion bores, and shaft for damage. Service as necessary.
Loss Of Lubricant	1. Lubricant level too high.	1. Drain lubricant to the correct level.
	2. Worn axle shaft seals.	2. Replace seals.
	3. Cracked differential housing.	3. Repair as necessary.
	4. Worn pinion seal.	4. Replace seal.
	5. Worn/scored flange.	5. Replace flange and seal.
	6. Axle cover not properly sealed.	6. Remove, clean and seal cover.
Axle Overheating	1. Lubricant level low.	1. Fill differential to correct level.
	2. Improper grade of lubricant.	2. Fill differential with the correct fluid type and quantity.
	3. Bearing preloads too high.	3. Adjust bearing preloads.
	4. Insufficient ring gear backlash.	4. Adjust ring gear backlash.
Gear Teeth Broke	1. Overloading.	1. Replace gears. Examine other gears and bearings for possible damage.
	2. Erratic clutch operation.	2. Replace gears and examine the remaining parts for damage. Avoid erratic clutch operation.
	3. Ice-spotted pavement.	3. Replace gears and examine remaining parts for damage.
	4. Improper adjustments.	4. Replace gears and examine remaining parts for damage. Ensure ring gear backlash is correct.
Axle Noise	1. Insufficient lubricant.	1. Fill differential with the correct fluid type and quantity.
	2. Improper ring gear and pinion adjustment.	2. Check ring gear and pinion contact pattern.
	3. Unmatched ring gear and pinion.	3. Replace gears with a matched ring gear and pinion.
	4. Worn teeth on ring gear and pinion.	4. Replace ring gear and pinion.
	5. Loose pinion bearings.	5. Adjust pinion bearing preload.
	6. Loose differential bearings.	6. Adjust differential bearing preload.
	7. Ring gear run-out.	7. Measure ring gear run-out. Replace components as necessary.
	8. Loose differential bearing cap bolts.	8. Inspect differential components and replace as necessary. Ensure that the bearing caps are torqued to the proper specification.
	9. Housing not machined properly.	9. Replace housing.

DIAGNOSTIC CHART

Scheme 166

Scheme 166: ADJUSTMENTS

Ring gear and pinion are supplied as a matched sets. Identifying numbers marked on the ring and pinion gears for production date, part number and matching number. A plus (+) number, minus (-) number or zero (0) will be marked on the pinion gear for depth variance. This first number is the amount (in thousandths of an inch) the depth varies from the standard depth setting of a pinion marked with a (0).

Pinion depth is adjusted with a select shim (1) located under the rear pinion bearing cup. Pinion bearing preload/torque to rotate is adjusted with a select shim (2) on the pinion shaft. Differential bearing preload and backlash is adjusted with select shims (3) located between the differential bearing cups and the housing.

Scheme 167

Scheme 167: PINION GEAR DEPTH

Measurement is taken with Height Block (special tool #6739, Block, Height) (1), Pinion Block (special tool #10091, Block, Gauge) (2), Screw (special tool #6741, Screw) (3), Nut (special tool #10121, Cone) (4), Arbor Discs (special tool #10094, Set, Arbor Disc) (5) and Arbor (special tool #D-115-3, Arbor) (6). With pinion bearing cups and pinion bearings installed in the housing, take measurements with Dial Indicator (special tool #C-3339A, Set, Dial Indicator) and Scooter Block (special tool #D-115-2A, Block, Scooter).

Scheme 168

Scheme 169

Scheme 170

Scheme 171

Scheme 172

Scheme 173

Scheme 174

Scheme 175

Scheme 176

Scheme 177

Assemble Pinion Height Block (special tool #6739, Block, Height) (1), Pinion Block (special tool #10091, Block, Gauge) (2) and rear pinion bearing onto Screw (special tool #6741, Screw).
Insert assembled pinion height block, pinion block, rear bearing and screw into the housing through pinion bearing cups.
Install front pinion bearing and Cone-Nut (special tool #10121, Cone) (1) onto Screw (special tool #6741, Screw) (2).
Tighten cone-nut (1) until Torque To Rotate (2) the screw is 1.7 - 2.26 N.m (15 - 20 in. lbs.).
Place Arbor Disc (special tool #10094, Set, Arbor Disc) (1) on Arbor (special tool #D-115-3, Arbor) (2), then position disc (1) in differential bearing cradles.
Install differential bearing caps (1) on arbor discs. Tighten larger bearing cap to 160 N.m (118 ft. lbs.) and small bearing to 100 N.m (74 ft. lbs.). NOTE: Arbor should rotate freely in the arbor disc.
Assemble Dial Indicator (special tool #C-3339A, Set, Dial Indicator) (1) into Scooter Block (special tool #D-115-2A, Block, Scooter) (2) and secure set screw.
Position Scooter Block (1) flush on the pinion height block. Hold scooter block and zero the dial indicator (2).
Slowly slide the scooter block (1) across the pinion height block over to the arbor (3). Move scooter block till dial indicator (2) crests the arbor (3), then record the highest reading. NOTE: If depth variance is -2, add 0.002 in. to the dial indicator reading. If the depth variance is +2, subtract 0.002 in. from the dial indicator reading.
Select a pinion depth shim equal to the dial indicator reading plus or minus the pinion depth variance number on the pinion gear.
Remove rear pinion bearing cup (1) with a hammer and brass drift (2).
Install pinion depth shim (1) in rear pinion bearing cup bore.
Install rear pinion bearing cup with Installer (special tool #10093, Installer, Bearing Cup) (1) and handle (special tool #C-4171, Driver Handle, Universal) (2).

Scheme 178

Scheme 178: PINION TORQUE TO ROTATE

Pinion torque to rotate/pinion bearing preload is achieved using a select shim (1). The shim is located on the pinion shaft on top of the spacer (2). Pinion preload shims thickness will change with pinion depth shim change.

Note. Pinion torque to rotate (PTTR) is measured without the pinion seal.

Scheme 179

Install pinion into the housing with the original shims plus/minus the pinion depth shim change. If pinion depth shim thickness was increased by 0.002 in. from the original shim thickness, increase preload shim thickness by 0.002 in. If pinion depth shim thickness was decreased by 0.002 in. from the original shim thickness, decrease preload shim thickness by 0.002 in.
Install pinion front bearing.
Install pinion flange and tighten the nut to 500 N.m (369 ft. lbs.)
Measure pinion torque to rotate (1) with and inch pound torque wrench (2). Pinion torque to rotate is: 5 - 8 N.m (44 - 70 in. lbs.).

Note. To increase PTTR install a thinner shim. To decreases PTTR install thicker shim. A shim thickness change of 0.025 mm (0.001 in.) will change PTTR approximately 0.9 N.m (8 in. lbs.).

DIFFERENTIAL BEARING PRELOAD AND GEAR BACKLASH

Before measuring differential bearing preload and gear backlash, pinion gear depth must be established and the pinion gear ready for installation. Pinion gear depth is essential to establishing gear backlash and tooth contact patterns.

Differential bearing preload and gear backlash is achieved with selective shims located between the differential bearing cups and differential housing. Shim thickness is determined using Dummy Bearings (special tool #10120, Bearings, Dummy) in place of the differential side bearings and preload shims.

Note. The large dummy bearings has 7 mm (0.275 in.) added to the thickness. This was done to eliminate the use of a dummy shim and differential spacer. The small dummy bearing has 3 mm (0.118) added to the thickness. This was done to eliminate the use of a dummy shim.

Scheme 180

Scheme 180: DIFFERENTIAL BEARING PRELOAD SHIM SELECTION

Scheme 181

Scheme 182

Scheme 183

Scheme 184

Scheme 185

Scheme 186

Scheme 187

Scheme 188

Remove bearings from differential case.
Install Dummy Bearings (special tool #10120, Bearings, Dummy) (1) on differential case (2).
Install differential case in the housing.
Install differential (1) bearing caps and tighten bearing cap bolts (2) finger tight.
Seat pinion gear side (1) dummy bearing with a dead-blow hammer (2).
Seat ring gear side (1) dummy bearing with a dead-blow hammer (2).
Tighten larger bearing cap to 160 N.m (118 ft. lbs.) and small bearing to 100 N.m (74 ft. lbs.).
Attach Dial Indicator (special tool #C-3339A, Set, Dial Indicator) (1) to the housing and position dial indicator plunger on a flat surface on the ring gear (2).
Push and hold differential case (3) to pinion gear side of the housing and zero dial indicator.
Push and hold differential case (3) to the ring gear (2) side and record differential dial indicator (1) reading. Add 6 mm (0.236 in.) to the dial indicator reading for dummy bearings thickness. Then add 0.2 mm (0.008 in) for bearing preload. This is the total shim thickness needed to preload the differential bearings. Example: Differential Dial Indicator Reading + Dummy Bearings 6 mm (0.236 in.) + Differential Bearing Preload 0.2 mm (0.008 in) = Total Differential Shim
Rotate dial indicator out of the way.
Remove differential case with dummy bearings from the housing.
Install pinion gear (1) into the housing.
Establish pinion (1) torque to rotating with torque wrench (2).
Install differential (2) with Dummy Bearings (special tool #10120, Bearings, Dummy) (1) into the housing.
Install differential (1) bearing caps and bearing cap bolts (2).
Seat differential dummy bearing to the ring gear side (1) of the housing with a dead-blow hammer (2).
Tighten larger bearing cap to 160 N.m (118 ft. lbs.) and small bearing to 100 N.m (74 ft. lbs.).
Attach Dial Indicator (special tool #C-3339A, Set, Dial Indicator) (1) to the housing and position dial indicator plunger on a flat surface on the ring gear (2).
Push and hold differential case (3) to pinion gear side of the housing and zero dial indicator.
Push and hold differential case (3) to the ring gear (2) side and record ring gear side dial indicator (1) reading. Add 3 mm (0.118 in.) to the record dial indicator reading to compensate for dummy bearing thickness. Then subtract 0.15 mm (0.006 in.) to compensate for ring gear backlash. The remainder is the total shim thickness needed on the ring gear side of the differential. Example: Ring Gear Side Dial Indicator Reading + One Dummy Bearing 3 mm (0.118 in.) - Ring Gear Backlash 0.15 mm (0.006 in.) = Ring Gear Side Shim
Subtract ring gear side shim from total differential shim, the remainder is the shim thickness needed on the pinion side of the housing. Example: Total Differential Shim - Ring Gear Side Shim = Pinion Gear Side Shim
Remove differential case with dummy bearings from the housing.
Install new side bearing cones and cups on differential case.
Mount Dial Indicator (special tool #C-3339A, Set, Dial Indicator) (1) to the housing (2) with indicator plunger against the opposite side of the housing. Zero the indicator.
Spread housing, while measuring the distance with the dial indicator. CAUTION: Never spread housing over 0.38 mm (0.015 in.). Failure to follow these instruction will damage the housing.
Remove dial indicator.
Install differential case (1) with bearing cups and shims (2) into the housing.
Rotate the differential case several times to seat the side bearings.
Remove Spreader (special tool #W-129-B, Spreader, Differential) and Adapter Plates (special tool #10068, Adapters, Spreader) (1) from housing (2).
Install differential (1) bearing caps and bolts (2).
Tighten larger bearing cap to 160 N.m (118 ft. lbs.) and small bearing to 100 N.m (74 ft. lbs.).

Scheme 189

Scheme 189: GEAR BACKLASH

Scheme 190

Position the dial indicator (1) plunger against a ring gear tooth (2).
Push and hold ring gear upward while not allowing the pinion gear to rotate.
Zero dial indicator face to pointer.
Push and hold ring gear downward while not allowing the pinion gear to rotate. Dial indicator reading should be between 0.1 - 0.15 mm (0.004 - 0.006 in.). If backlash is not within specifications transfer the necessary amount of shim thickness from one side of the differential housing to the other.
Verify differential case and ring gear runout by measuring ring to pinion gear backlash at eight locations around the ring gear. Readings should not vary more than 0.05 mm (0.002 in.). If readings vary more than specified, the ring gear or the differential case is defective.
If backlash is not within specifications adjust shims equally on both sides to obtain backlash specification.

After the proper backlash is achieved, perform the GEAR TOOTH CONTACT PATTERN procedure.

Scheme 191

Scheme 191: GEAR TOOTH CONTACT PATTERN

The gear and pinion gear tooth contact patterns will show if the ring gear backlash has been adjusted correctly.

Ring and pinion gear tooth description

Toe - (1)
Land - (2)
Drive Side - (3)
Root - (4)
Heel - (5)
Coast Side - (6)

Paint six ring gear teeth 180 degrees apart with marking compound. Rotate the pinion 4 full revolutions in each directions to obtain a contact pattern.

Scheme 192

Gear contact pattern correct. Backlash and pinion depth is correct.

Scheme 193

Ring gear too far away from pinion gear, coast side toe (1) and drive side heel (2). Decrease backlash, by moving the ring closer to the pinion gear.

Scheme 194

Ring gear too close to pinion gear, drive side toe (1) and coast side heel (2). Increase backlash, by moving the ring away from the pinion gear.

Scheme 195

Ring gear too far away from pinion gear, drive side heel (1) and coast side heel (2). Decrease backlash, by moving the ring closer to the pinion gear.

Scheme 196

Ring gear too close to pinion gear, drive side toe (1) and coast side toe (2). Increase backlash, by moving the ring away from the pinion gear.

Scheme 197

Pinion gear is set too low. Increase pinion gear height, by increasing the pinion depth shim thickness.

Scheme 198

Pinion gear is set too high. Decrease pinion depth, by decreasing the pinion depth shim thickness.

DIFFERENTIAL BEARING PRELOAD CHECK

The final check on the differential assembly before installing the axles is torque to rotate pinion and differential combined. This will verify the correct differential bearing preload.

Total Torque To Rotate (TTTR) the differential is: Pinion Torque To Rotate plus 1.5 N.m ± 0.5 N.m (13 in. lbs. ± 4.4 in. lbs.).

Note. If TTTR is too high, decrease shim thickness equally from both sides of the differential and check TTTR again. If TTTR is too low, increase shim thickness equally to both sides of the differential and check TTTR again.

Front Axle - 275FBI: Other RAM Pickup 2500