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Backlash Adjustment (8.6 Inch Axle): Procedure

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    Fig 1: Measuring Pinion Rotating Torque
    GM661077Courtesy of GENERAL MOTORS CORP.
  1. Using an inch-pound torque wrench, measure the rotating torque of the drive pinion and differential assembly.

    Specification:  The rotating torque of the drive pinion and differential assembly should be 2.3-4.5 N.m (20-40 lb in) for new bearings or 1.7-3.4 N.m (15-30 lb in) for used bearings.

  2. If the rotating torque is too low, tighten the differential bearing adjuster nut in 1 slot increments until the specified rotating torque is obtained.
  3. If the rotating torque is too high, loosen the differential bearing adjuster nut in 1 slot increments until the specified rotating torque is obtained.
  4. If the specification for the rotating torque of the drive pinion and differential assembly cannot be obtained by adjusting the differential bearing adjuster nut, remove the differential assembly, measure the rotating torque of the drive pinion and adjust as necessary. Refer to Differential Replacement (10.5 Inch Axle)  or Differential Replacement (8.6 Inch Axle)  and Drive Pinion Bearings Replacement (8.6 Inch Axle)  or Drive Pinion Bearings Replacement (10.5 Inch Axle) .
    5. Fig 2: Measuring Ring Gear Backlash
    GM6946Courtesy of GENERAL MOTORS CORP.
  5. Install the J 25025-1  and the J 8001-3  to the axle housing as shown.
  6. Place the indicator stem of the J 8001-3  at the heel end of a gear tooth.
  7. Set the J 8001-3  so that the stem is aligned with the gear rotation and perpendicular to the tooth angle.
  8. Preload the dial of the J 8001-3  approximately 3/4 of a turn.

    Align the needle and the dial face of the J 8001-3  to ZERO.

  9. While holding the drive pinion stationary, move the ring gear back and forth.

    Measure and record the backlash.

  10. 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).

  11. 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
  12. 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).

    13. IMPORTANT: Increasing or decreasing the shim thickness by 0.05 mm (0.002 in) will change the backlash adjustment approximately 0.03 mm (0.001 in).
  13. If the backlash is not within specifications, adjust the backlash by performing the following procedure:
    1. Remove the differential bearing adjuster nut retainer bolt.
    2. Remove the differential bearing adjuster nut retainer.
    3. Loosen the bearing cap bolts.
  14. Do not remove the bearing cap bolts.
    1. Loosen the differential bearing adjuster nut using the J 24429  . See Special Tools .
    2. Remove the differential side bearing shim.
    3. Measure the thickness of the shim.
  15. Calculate the average of the 3 measurements.
  16. Record the measurement.
    • If the backlash is too small, select a smaller shim than the one that was removed. For example, to increase the backlash by 0.05 mm (0.002 in), select a shim that is 0.10 mm (0.004 in) thinner than the shim that was removed.
    • If the backlash is too large, select a larger shim than the one that was removed. For example, to increase the backlash by 0.05 mm (0.002 in), select a shim that is 0.10 mm (0.004 in) thicker than the shim that was removed.
    • Install the shim.
  17. Tighten the differential bearing adjuster nut using the J 24429  until the differential bearing adjuster nut is seated against the bearing cup. See Special Tools .
  18. Once the differential bearing adjuster is seated against the differential bearing, tighten the differential bearing adjuster nut using the J 24429  the following additional amounts:. See Special Tools .

    Tighten: 

    • For used bearings, tighten the differential bearing adjuster nut an additional 2 slots.
    • For new bearings, tighten the differential bearing adjuster nut an additional 3 slots.

    19. NOTE: Refer to Fastener Notice .
  19. Tighten the differential bearing cap bolts.

    Tighten:  Tighten the bearing cap bolts to 85 N.m (63 lb ft).

  20. Recheck the backlash following the steps above to verify that the backlash is within specifications.
  21. Install the differential bearing adjuster nut retainer.
  22. Install the differential bearing adjuster nut retainer bolt.

    Tighten:  Tighten the differential bearing adjuster nut retainer nut bolt to 26 N.m (19 lb ft).

  23. Measure the drive pinion and differential case side bearing preload and adjust, if necessary following the steps above.
  24. Once the backlash and bearing preload 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 .
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