The axle receives power from the transmission through the propeller shaft. The propeller shaft is connected to the
pinion gear which rotates the differential through the gear mesh with the ring gear bolted to the differential case. The
engine power is transmitted to the axle shafts through the pinion mate and side gears. The side gears are splined
to the axle shafts.

DIAGNOSIS AND TESTING - REAR DIFFERENTIAL NOISE

GEAR NOISE

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 gears and pinions can be checked by turning the vehicle. They usually do not cause noise during
straight-ahead driving when the gears are unloaded. The side gears are loaded during vehicle turns. A worn pinion
shaft can also cause a snapping or a knocking noise.

BEARING NOISE

The halfshafts, differential and pinion bearings can all produce noise when worn or damaged. Bearing noise can be
either a whining, or a growling sound.

Pinion bearings have a constant-pitch noise. This noise changes only with vehicle speed. Pinion bearing noise will
be higher pitched because it rotates at a faster rate. Drive the vehicle and load the differential. If bearing noise
occurs, the rear pinion bearing is the source of the noise. If the bearing noise is heard during a coast, the front
pinion bearing is the source.

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REAR DIFFERENTIAL

Worn or damaged differential bearings usually produce a low pitch noise. Differential bearing noise is similar to
pinion bearing noise. The pitch of differential bearing noise is also constant and varies only with vehicle speed.

Rear wheel hub bearings produce noise and vibration when worn or damaged. The noise generally changes when
the bearings are loaded. Road test the vehicle. Turn the vehicle sharply to the left and to the right. This will load the
bearings and change the noise level. Where bearing damage is slight, the noise is usually not noticeable at speeds
above 30 mph.

LOW SPEED KNOCK

Low speed knock is generally caused by worn universal joints. A worn pinion shaft bore will also cause a low speed
knock.

VIBRATION

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

•

Damaged propeller shaft.

•

Missing propeller shaft balance weight(s).

•

Worn or out-of-balance wheels.

•

Loose wheel studs.

•

Worn U-joint(s).

•

Damaged rear wheel hub bearings.

•

Loose pinion gear nut.

•

Excessive pinion yoke run out.

•

Damaged halfshafts.

Check for loose or damaged front-end components or engine/transmission mounts. These components can contrib-
ute to what appears to be a rear end vibration. Do not overlook engine accessories, brackets and drive belts.

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.

•

Worn U-joints.

•

Loose pinion gear nut and yoke.

•

Excessive ring gear backlash.

•

Excessive side gear to case clearance.

•

Damaged halfshafts.

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

REAR DIFFERENTIAL

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DIAGNOSTIC CHART

CONDITION

POSSIBLE CAUSES

CORRECTION

WHEEL NOISE

1. Wheel loose.

1. Tighten loose wheel bolts.

2. Faulty wheel hub bearing.

2. Replace bearing.

DIFFERENTIAL CRACKED

1. Improper adjustment of the
differential bearings.

1. Replace differential.

2. Excessive ring gear backlash.

2. Replace differential.

3. Erratic clutch operation.

3. Replace differential.

DIFFERENTIAL GEARS SCORED

1. Insufficient lubrication.

1. Replace differential. Fill
differential with the correct fluid type
and quantity.

2. Improper grade of lubricant.

2. Replace differential. Fill
differential with the correct fluid type
and quantity.

LOSS OF LUBRICANT

1. Lubricant level too high.

1. Drain lubricant to the correct
level.

2. Worn differential side seals.

2. Replace seals.

3. Cracked differential housing.

3. Replace as necessary.

4. Worn pinion seal.

4. Replace seal.

5. Worn/scored yoke.

5. Replace yoke and seal.

6. Differential cover not properly
sealed.

6. Remove, clean, and reseal 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.

GEAR TEETH BROKE

1. Overloading.

1. Replace differential.

2. Erratic clutch operation.

2. Replace differential.

3. Ice-spotted pavement.

3. Replace differential.

4. Improper adjustments.

4. Replace differential.

DIFFERENTIAL NOISE

1. Insufficient lubricant.

1. Fill differential with the correct
fluid type and quantity.

2. Improper ring gear and pinion
adjustment.

2. Replace differential.

3. Unmatched ring gear and pinion.

3. Replace differential.

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

4. Replace differential.

5. Loose pinion bearings.

5. Replace differential.

6. Loose differential bearings.

6. Replace differential.

7. Misaligned or sprung ring gear.

7. Replace differential.

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