Backlash Adjustment (All Except 9.75 Inch Axle)

Tools Required

• J 8001  Dial Indicator Set
• J 23409  Dial Indicator Extension
• J 25588  Side Bearing Shim Installer

1. Install the differential case with the bearing cups into the rear axle.
2. Determine the differential side bearing preload. Refer to Differential Side Bearing Preload Adjustment .
3. Install the differential bearing caps and the bolts.
   NOTE: Use the correct fastener in the correct location. Replacement fasteners must be the correct part number for that application. Fasteners requiring replacement or fasteners requiring the use of thread locking compound or sealant are identified in the service procedure. Do not use paints, lubricants, or corrosion inhibitors on fasteners or fastener joint surfaces unless specified. These coatings affect fastener torque and joint clamping force and may damage the fastener. Use the correct tightening sequence and specifications when installing fasteners in order to avoid damage to parts and systems.

   Tighten 

   Tighten the bolts to 75 N.m (55 lb ft).

4. Rotate the case several times in order to seat the bearings.
5. Install the J 8001 and the J 23409 to the axle housing as shown.
Fig 1: Installing J 8001 And J 23409 To Axle Housing
Courtesy of GENERAL MOTORS CORP.
6. Place the indicator stem of the J 8001 at the heel end of a gear tooth.
7. Set the J 8001 so that the stem is aligned with the gear rotation and perpendicular to the tooth angle.
8. While holding the pinion stationary, move the ring gear back and forth.

   Measure and record the backlash.

9. Repeat the measuring procedure at eight points around the ring gear.

   Specification 

   The difference between the backlash at all of the measuring points should not vary by more than 0.05 mm (0.002 in).

10. If the difference between the backlash at all of the measuring points varies by more than 0.05 mm (0.002 in), inspect for the following conditions:
    • Burrs
    • A distorted case flange
    • Uneven bolting
11. If the difference between all the measuring points is within specifications, the backlash at the minimum lash point measured should be:

    Specification 

    The backlash between the ring gear and the drive pinion should be between 0.08- 0.25 mm (0.003-0.010 in) with a preferred backlash of 0.13-0.18 mm (0.005-0.007 in).

    IMPORTANT:

    • Do not use the original cast iron production shims to adjust the backlash. Use service shim and spacers instead.
    • Adjust the thickness of the shim pack on each side of the differential in equal amounts. This will maintain the correct axle side bearing preload.
    • Moving 0.05 mm (0.002 in) of shim thickness from one side of the differential to the other will change the backlash adjustment by 0.03 mm (0.001 in).
12. If the backlash is too small, increase the backlash using the following procedure:
    1. 12.1. Remove the appropriate amount of thickness from the left side shim pack. For example, to increase the backlash by 0.10 mm (0.004 in), subtract 0.20 mm (0.008 in) of thickness from the left side shim pack.
    2. 12.2. Add the 0.20 mm (0.008 in) of shim thickness to the right side shim pack.
    3. 12.3. Recheck the backlash and adjust as necessary.
13. If the backlash is too large, decrease the backlash using the following procedure:
    1. 13.1. Remove the appropriate amount of thickness from the right side shim pack. For example, to decrease the backlash by 0.10 mm (0.004 in), subtract 0.20 mm (0.008 in) of thickness from the right side shim pack.
    2. 13.2. Add the 0.20 mm (0.008 in) of shim thickness to the left side shim pack.
    3. 13.3. Recheck the backlash and adjust as necessary.
14. When you have correctly adjusted the backlash, remove the bearing caps and the shim packs.
15. Select a shim 0.10 mm (0.004 in) thicker than the one removed from the left side. Insert this shim between the spacer and the left bearing race.
16. Install the left bearing cap and bolts. Do not tighten.
17. Select a shim 0.10 mm (0.004 in) thicker than the shim removed from the right side. Insert the shim between the spacer and the right bearing race. Drive the shim into place using the J 25588.
Fig 2: Driving Shim Into Place
Courtesy of GENERAL MOTORS CORP.
18. Install the right side bearing cap and bolts.

    Tighten 

    Tighten the bolts to 75 N.m (55 lb ft).

19. Recheck the backlash and adjust as necessary.
20. Once backlash is correct, perform a gear tooth contact pattern check in order to ensure proper alignment between the ring and pinion gears. Refer to Gear Tooth Contact Pattern Inspection .