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Special Tools

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    NOTE:
    • Ensure that the side bearing surfaces in the axle housing are clean and free of burrs. If the original bearings are to be reused, the original bearing cups must also be used.
    • The differential side bearings must be initially preloaded in order to determine the backlash of the gear set. After the backlash is set, the final bearing preload is set.
  1. Measure the rotating torque of the drive pinion and differential assembly. Refer to Differential Drive Pinion Gear Bearing Replacement (8.6 Inch Axle) , Differential Drive Pinion Gear Bearing Replacement (10.5 Inch Axle) .
    2. Fig 1: Measuring Ring Gear Backlash
    GM6946Courtesy of GENERAL MOTORS COMPANY
  2. Install the J 25025  pins and the J 8001  indicator to the axle housing.
    3. NOTE:

    Preload the dial of the approximately 3/4 of a turn and zero the gauge.

  3. Set the J 8001  indicator so that the stem is aligned with the gear rotation and square to the tooth angle.
  4. Hold the drive pinion stationary, move the ring gear back and forth.
  5. Repeat the measuring procedure at eight points around the ring gear.
  6. 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 burrs, a distorted case flange or uneven bolting.
  8. If the difference between all the measuring points is within specifications, the backlash at the minimum lash point measured should be 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).
    9. NOTE:
    • Do not use the original cast iron production shims to adjust the backlash. Use service shims 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 approximately 0.03 mm (0.001 in).
  9. If the backlash is too small, increase the backlash using the following procedure:
      NOTE:

      Mark the bearing caps left or right.

    1. Remove the bearing cap bolts and the bearing caps.
      2. NOTE:

      Mark the bearing cups and the shims left or right.

    2. Remove the differential case assembly with the bearing cups and the shims.
      3. NOTE:
      • Measure the production shim or the shim and service spacer in 3 locations.
      • Measure each shim separately.
    3. Measure the thickness of left side shim pack.
      4. NOTE:
      • Add the average of each of the shim measurements together.
      • Record the measurement. This is the thickness for the left side shim pack.
    4. Calculate the average of the 3 measurements for each shim.
      5. NOTE:

      If the original shim is cast iron production shim, assemble the shim pack using a service spacer and service shims. For example, to increase the backlash by 0.05 mm (0.002 in), remove 0.10 mm (0.004 in) of thickness from the left side shim pack.

    5. Assemble a new left side shim pack by decreasing the appropriate amount of thickness from the original left side shim pack.
      6. NOTE:

      Measure each shim separately.

    6. Measure the thickness of right side shim or the shim and service spacer in 3 locations.
      7. NOTE:
      • Add the average of each of the shim measurements together.
      • Record the measurement. This is the thickness for the right side shim pack.
    7. Calculate the average of the 3 measurements for each shim.
    8. Assemble a new right side shim pack by increasing the appropriate amount of thickness to the original right side shim pack. If the original shim is cast iron production shim, assemble the shim pack using a service spacer and service shims. For example, to increase the backlash by 0.05 mm (0.002 in), add 0.10 mm (0.004 in) of thickness to the right side shim pack.
  10. Use the following procedure to decrease the backlash if the backlash is too large:
      NOTE:

      Mark the bearing caps left or right.

    1. Remove the bearing cap bolts and the bearing caps.
      2. NOTE:

      Mark the bearing cups and the shims left or right.

    2. Remove the differential case assembly with the bearing cups and the shims.
      3. NOTE:
      • Measure the production shim or the shim and service spacer in 3 locations.
      • Measure each shim separately.
    3. Measure the thickness of left side shim pack.
      4. NOTE:
      • Add the average of each of the shim measurements together.
      • Record the measurement. This is the thickness for the left side shim pack.
    4. Calculate the average of the 3 measurements for each shim.
    5. Assemble a new left side shim pack by increasing the appropriate amount of thickness to the original left side shim pack. If the original shim is cast iron production shim, assemble the shim pack using a service spacer and service shims. For example, to increase the backlash by 0.05 mm (0.002 in), add 0.10 mm (0.004 in) of thickness to the left side shim pack.
      6. NOTE:
      • Measure the shim or the shim and service spacer in 3 locations.
      • Measure each shim separately.
    6. Measure the thickness of right side shim pack.
      7. NOTE:
      • Add the average of each of the shim measurements together.
      • Record the measurement. This is the thickness for the right side shim pack.
    7. Calculate the average of the 3 measurements for each shim.
    8. Assemble a new right side shim pack by decreasing the appropriate amount of thickness to the original right side shim pack. If the original shim is cast iron production shim, assemble the shim pack using a service spacer and service shims. For example, to decrease the backlash by 0.05 mm (0.002 in), remove 0.10 mm (0.004 in) of thickness to the right side shim pack.
  11. Install the differential case assembly with the bearing cups.
  12. Install the left side service spacer between the axle housing and the differential case.
  13. Install the right side service spacer between the axle housing and the differential case.
    14. Fig 2: Installing The Left Side Service Shim Using J 25588
    GM688991Courtesy of GENERAL MOTORS COMPANY
    NOTE:

    The service shim or shims must be installed between the service spacer and the differential bearing cup.

  14. Using the J 25588  installer, install the left side service shim or shims.
    15. NOTE:

    The service shim or shims must be installed between the service spacer and the differential bearing cup.

  15. Using the J 25588  installer, install the right side service shim or shims.
    16. CAUTION:

    Refer to Fastener Caution .

  16. Install the bearing caps and bolts and tighten to 75 N.m (55 lb ft).
  17. Recheck the backlash and adjust, if necessary.
  18. 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 .
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