Backlash Adjustment (9.75 Inch Axle)

Tools Required

• J 25025  Guide Pins. See Special Tools and Equipment .
• J 8001  Dial Indicator

1. Determine the differential side bearing preload and initial backlash. Refer to Differential Side Bearing Preload Adjustment (8.6 Inch Axle)  or Differential Side Bearing Preload Adjustment (9.5 Inch Axle)  or Differential Side Bearing Preload Adjustment (9.75 Inch Axle)  or Differential Side Bearing Preload Adjustment (10.5 Inch, 11.5 Inch Axles) .
2. Install the J 25025  (1) and the J 8001  (2, 3) to the axle housing as shown.
Fig 1: Installing J 25025 & J 8001 To The Axle Housing
Courtesy of GENERAL MOTORS CORP.
3. Place the indicator stem of the J 8001  at the heel end of a gear tooth.
4. Set the J 8001  so that the stem is aligned with the gear rotation and perpendicular to the tooth angle.
5. While holding the pinion stationary, move the ring gear back and forth.

   Measure and record the backlash.

6. 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).

7. 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
8. 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 0.13-0.20 mm (0.005-0.008 in).

IMPORTANT: 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.
9. If the backlash is not within specifications, adjust the backlash by doing the following:
   1. Remove the differential side bearings. Refer to Differential Side Bearings Replacement (All Except 9.75 Inch Axle)  or Differential Side Bearings Replacement (9.75 Inch Axle) .
   2. If the backlash is too small, increase the backlash using the following procedure:
      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.
         IMPORTANT: 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).
      2. Add the 0.20 mm (0.008 in) of shim thickness to the right side shim pack.
   3. If the backlash is too large, decrease the backlash using the following procedure:
      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.
         IMPORTANT: 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).
      2. Add the 0.20 mm (0.008 in) of shim thickness to the left side shim pack.
10. Install the left and right shim packs onto the differential case.
11. Install the differential side bearings. Refer to Differential Side Bearings Replacement (All Except 9.75 Inch Axle)  or Differential Side Bearings Replacement (9.75 Inch Axle) .
12. Recheck the backlash and adjust as necessary.
13. 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 .