Chevrolet Silverado / GMC Sierra. Service manual — part 1391

The effects of bearing preloads are not readily apparent on hand-loaded tooth contact pattern
tests. However, bearing preloads should be within specifications before proceeding with backlash
and pinion depth adjustments.

Pinion Depth Adjustment

Adjust the position of the pinion by increasing or decreasing the distance between the pinion head
and the centerline of the ring gear. Decreasing the distance moves the pinion closer to the
centerline of the ring gear. Increasing the distance moves the pinion farther away from the
centerline of the ring gear.

Backlash Adjustment

Adjust the backlash by means of moving the side bearing adjuster sleeves which move the case
and ring gear assembly closer to or farther from the pinion. Also use the adjuster sleeves in order
to set the side bearing preload.

If the left side adjuster sleeve is moved in, along with an equal outward movement of the
right side adjuster, the backlash will increase.

If the left side adjuster sleeve is moved out, along with an equal inward movement of the
right side adjuster, the backlash will decrease.

Testing Procedure

1. Wipe clean the differential case, the ring gear and the differential carrier housing of

lubricant. Carefully clean each tooth of the ring gear.

2008 Chevrolet Silverado 1500

2008 Driveline/Axle Front Drive Axle - Cab & Chassis Sierra, Cab & Chassis Silverado, Sierra & Silverado

Fig. 240: Ring Gear Teeth Pattern
Courtesy of GENERAL MOTORS CORP.

2. Use a medium stiff brush in order to sparingly apply gear marking compound GM P/N

1052351 (Canadian P/N 10953497) or equivalent to all of the ring gear teeth.

3. Using a wrench, turn the drive pinion flange/yoke so that the ring gear rotates at least 3 full

revolutions.

4. Turn the drive pinion flange/yoke in the opposite direction so that the ring gear rotates at

least 3 full revolutions in the opposite direction.

5. Observe the pattern on the ring gear teeth. Compare the pattern with the following

illustrations.

6. Once the proper pattern is obtained, continue the assembly of differential carrier. Refer to

IMPORTANT: Avoid turning the ring gear excessively.

2008 Chevrolet Silverado 1500

2008 Driveline/Axle Front Drive Axle - Cab & Chassis Sierra, Cab & Chassis Silverado, Sierra & Silverado

Differential Carrier Assembly Assemble (8.25 Inch Axle Lock Ring Style) or
Differential Carrier Assembly Assemble (9.25 Inch Axle).

Correct Contact Pattern

Condition

Fig. 241: Identifying Correct Gear Tooth Contact Pattern
Courtesy of GENERAL MOTORS CORP.

The backlash and pinion depth is correct.

Correction

None required.

Service Hints

Loose bearing on the drive pinion or in the differential case may cause patterns that vary. If the
contact pattern varies, inspect the following preload settings:

Total assembly

Differential case

Drive pinion

2008 Chevrolet Silverado 1500

2008 Driveline/Axle Front Drive Axle - Cab & Chassis Sierra, Cab & Chassis Silverado, Sierra & Silverado

If these settings are correct, inspect for damage or incorrectly assembled parts.

Drive Side Heel - Coast Side Toe Contact Pattern

Fig. 242: Identifying Drive Side Heel - Coast Side Toe Contact Pattern
Courtesy of GENERAL MOTORS CORP.

Condition

The pinion depth is incorrect. The drive pinion is too far away from the ring gear.

Correction

Adjust the pinion depth of drive pinion. Refer to Pinion Depth Adjustment.

Drive Side Toe - Coast Side Heel Contact Pattern

2008 Chevrolet Silverado 1500

2008 Driveline/Axle Front Drive Axle - Cab & Chassis Sierra, Cab & Chassis Silverado, Sierra & Silverado