Axle gear noise can be caused by insufficient lubricant, incorrect backlash, incorrect pinion depth, tooth contact,
worn/damaged gears, or the carrier housing not having the proper offset and squareness.

Gear noise usually happens at a specific speed range. The noise can also occur during a specific type of driving
condition. These conditions are acceleration, deceleration, coast, or constant load.

When road testing, first warm-up the axle fluid by driving the vehicle at least 5 miles and then accelerate the vehicle
to the speed range where the noise is the greatest. Shift out-of-gear and coast through the peak-noise range. If the
noise stops or changes greatly check for:

•

Insufficient lubricant.

•

Incorrect ring gear backlash.

•

Gear damage.

Differential side and pinions gears, usually do not cause noise during straight-ahead driving, when the gears are
unloaded. The side gears are loaded during turns. A worn pinion mate shaft can also cause a snapping or a knock-
ing noise.

BEARING NOISE

Bearing noise can be either a whining or a growling sound.

Pinion bearings have a constant high pitch noise, because it rotates at a faster rate. This noise changes with
vehicle speed. If noise is heard under a load, the rear pinion bearing is the source. If noise is heard during a coast,
the front pinion bearing is the source.

Differential bearings usually produce a low pitch noise. The differential bearing noise is constant and varies only
with vehicle speed.

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Axle shaft bearing noise generally changes when the bearings are loaded. Turn vehicle sharply to the left and the
right during a road test. This will load and unload the bearings and change the noise level. If axle bearing damage
is slight, the noise is usually not noticeable at speeds above 30 m.p.h.

LOW SPEED KNOCK

Low speed knock is generally caused by:

•

Worn U-joints or C/V joints.

•

Worn side-gear thrust washers

•

Worn pinion shaft bore.

VIBRATION

Vibration at the rear of the vehicle is usually caused by:

•

Damaged drive shaft.

•

Missing drive shaft balance weight(s).

•

Worn or out of balance wheels.

•

Loose wheel lug nuts.

•

Worn U-joints or C/V joints.

•

Loose/broken springs.

•

Damaged axle shaft bearing(s).

•

Loose pinion gear nut.

•

Excessive pinion yoke run out.

•

Bent axle shaft(s).

Check for loose or damaged front-end components or engine/transmission mounts. These components can contrib-
ute to what appears to be an axle vibration. Also look at engine accessories, brackets and drive belts.

NOTE: All driveline components should be examined before starting any repair.

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 or C/V joints.

•

Loose spring mounts.

•

Loose pinion gear nut and yoke.

•

Excessive ring gear backlash.

•

Excessive side gear to case clearance.

To determined the source of a snap/clunk noise, raise vehicle on a hoist with the wheels free to rotate. Have a
helper shift the transmission into gear and listen for the noise.

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REAR AXLE - 8 1/4

DIAGNOSTIC CHART

Condition

Possible Causes

Correction

Wheel Noise

1. Wheel loose.

1. Tighten loose nuts.

2. Faulty, brinelled 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.

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 pre-load 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 yoke.

5. Replace yoke and seal.

6. Axle cover not properly sealed.

6. Remove, clean, and re-seal cover.

REAR AXLE - 8 1/4

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Condition

Possible Causes

Correction

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 pre-loads too high.

3. Re-adjust bearing pre-loads.

4. Insufficient ring gear backlash.

4. Re-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. Adjust backlash or pinion depth.

3. Unmatched ring gear and pinion.

3. Replace gears with a matched ring
gear and pinion.

4. Worn teeth on ring gear and/or
pinion.

4. Replace ring gear and pinion.

5. Loose pinion bearings.

5. Adjust pinion bearing pre-load.

6. Loose differential bearings.

6. Adjust differential bearing pre-load.

7. Mis-aligned or sprung ring gear.

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 tot he proper
specification.

9. Housing not machined properly.

9. Replace housing.

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