For 1990-2009 cars

Inspect the rear axle before disassembly. A close inspection of the rear axle and the report of the malfunction will aid in determining the type of repairs or adjustments that are necessary.

The following conditions may cause rear axle noise:

• | Improper backlash

• | The differential drive pinion gear inner bearing preload

• | The differential drive pinion gear outer bearing preload

• | The differential side bearing preload

• | Any combination of the above items

Measure the following items before removing the differential case from the housing:

• | The backlash

• | The total differential preload

• | The tooth contact pattern

Record and analyze the above measurements before removing the differential case from the housing.

Do not allow foreign matter (such as dirt or sand) near the rear axle. The presence of foreign matter in the rear axle may cause rear axle failure.

### Differential Ring Gear Tooth Nomenclature

The drive side (5) of the differential ring gear tooth curves outward, or is convex.

The coast side (3) of the differential ring gear tooth curves inward, or is concave.

The toe end (2) of the differential ring gear tooth is the end that is nearest to the center of the differential ring gear.

The heel end (1) of the differential ring gear tooth is the end that is farthest away from the center of the differential ring gear. The toe end of the tooth is smaller than the heel end.

### Effects Of Increasing Load On Tooth Contact Pattern

The load on the differential ring and the drive pinion gear is increased during vehicle acceleration.

An increased load on the differential ring and the drive pinion gear may cause the tooth contact to spread out. Under a very heavy load, the tooth contact may extend from the near to the near heel on the drive side.

Increasingly heavier loads cause the following changes in tooth contact:

• | The entire contact tends to shift toward the heel

• | The entire contact becomes broader with respect to the tops and the bottoms of the teeth

The following tooth contact pattern test will recreate the effects of a light load. For this reason, the patterns that will be obtained by the following test will only extend to about half of their potential expansion.

It is important to note that the contact pattern is centrally located up and down on the face of the differential ring gear teeth.

The following conditions may cause a change in the tooth contact pattern under a load:

• | A drive pinon gear is insufficiently preloaded

• | The differential bearings are insufficiently preloaded

### Adjustments Affecting Tooth Contact

The following two adjustments will affect the tooth contact pattern:

• | An adjustment to the backlash

• | An adjustment to the position of the drive pinion gear in the rear axle housing

The effects of bearing preloads are not readily apparent on hand-loaded tooth contact pattern tests.

Differential bearing shims can be used in order to adjust the backlash. The shims move the entire differential closer to or farther from the drive pinion gear.

Bearing shims can also be used in order to set the differential bearing preload.

• | Make the following changes in order to increase the backlash:

- | Increase the thickness of the right bearings shim

- | Decrease the thickness of the left bearing shim

• | Make the following changes in order to decrease the backlash:

- | Decrease the thickness of the right bearings shim

- | Increase the thickness of the left bearing shim

The position of the drive pinion gear can be adjusted by changing the thickness of the shims between the following components:

• | The drive pinion gear head

• | The race of the differential drive pinion gear inner bearing

The drive pinion gear shim is used in the rear axle in order to compensate for manufacturing tolerances.

• | Increasing the shim thickness moves the drive pinion gear closer to the centerline of the differential ring gear.

• | Decreasing shim thickness moves the drive pinion gear farther away from the centerline of the differential ring gear.

### Effects Of Differential Drive Pinion Gear Position On Tooth Pattern

The following tooth contact pattern exists when the differential drive pinion gear is too far away from the centerline of the differential ring gear:

• | High heel (2) contact on the drive side (4)

• | High toe (1) contact on the coast side (3)

Decreasing backlash in order to move the differential drive pinion gear closer to the centerline of the differential ring gear will cause the following tooth contact pattern:

• | High heel (2) contact on the drive side (4) moves down and toward the toe (1).

• | High toe (1) contact on the coast side (3) moves down and toward the heel (2).

The following tooth contact pattern exists when the differential drive pinion gear is too close to the centerline of the differential ring gear:

• | Low toe (1) contact on the drive side (4)

• | Low heel (2) contact on the coast side (3)

Increasing backlash in order to move the differential drive pinion gear further away from the centerline of the differential ring gear will cause the following tooth contact pattern to exist:

• | Low toe contact on the drive side (4) moves up and toward the heel (2).

• | Low heel contact on the coast side (3) moves up and toward the toe (1).