GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Pontiac 🢒 1999 🢒 Firebird 🢒 Driveline/Axle 🢒 Rear Drive Axle 🢒 Differential Carrier Bearing Preload Adjustment

Perform the differential bearing preload adjustment before installing the drive pinion gear. If the drive pinion gear is installed, remove the ring gear. Refer to Rear Axle Assemble .

When adjusting the differential bearing preload, change the thickness of both the right and the left bearing shims by an equal amount. This will ensure that the original backlash remains constant.

Production bearing shims are cast iron. Production bearing shims vary in thickness from 5.33-6.91 mm (0.210-0.272 in) in increments of 0.05 mm (0.002 in).

Steel service bearing shims are available from 1.02-2.08 mm (0.040-0.082 in) in increments of 0.05 mm (0.002 in).

Standard service bearing spacers are 4.32 mm (0.170 in) thick.

Refer to Production Differential Bearing Shim Thickness (Standard Spacer) and Service Differential Bearing Shim Thickness (Standard Spacer) in Rear Axle Specifications .

Important: 

   • Do not reinstall the production bearing shims. The production bearing shims may break when tapped by a hammer.
   • Service bearing shims are reusable. The differential bearings must have the original outer races in place when the bearings are reused.

  1. Determine the approximate required thickness of the replacement bearing shims. Measure each production bearing shim, each service bearing spacer, and each bearing shim pack.
  2. Determine the necessary service bearing shims. Select a starting point in service bearing shim thickness. Refer to Service Differential Bearing Shim Thickness (Standard Spacer) in Rear Axle Specifications .
  3. Position the following components into the rear axle housing:
    4. • The differential case
    • The differential bearing outer races
  4. Slip the correct service bearing spacer between each differential bearing race and the rear axle housing. Place the chamfered edge of the service bearing spacer against the rear axle housing.

    5. Notice: Install the left side bearing cap loosely so the differential case may be moved while checking adjustments. Another differential bearing cap bolt/screw can be added in the lower right side differential bearing cap hole. This will prevent the case from dropping while making shim adjustments.

  5. Select one or two bearing shims. Refer to Service Differential Bearing Shim Thickness in Rear Axle Specifications for the correct total thickness.

  6. Position the shims between the right side of the differential bearing race and the service bearing spacer.

    7. Position the left side of the differential bearing race and the bearing spacer against the left side of the rear axle housing.

  7. Insert progressively larger feeler gauge sizes between the right bearing shim and the service bearing spacer until you notice an increase in drag.

    8. The following measurements are examples of progressively larger feeler gauge sizes:

    • 0.25 mm (0.010 in)
    • 0.30 mm (0.012 in)
    • 0.36 mm (0.014 in)
  8. Push a feeler gauge downward until the end of the gauge touches the rear axle housing bore. This position will ensure an accurate reading. You have selected the correct feeler gauge thickness at the point just before additional drag begins.
  9. In order to ensure an even reading, rotate the differential case while using the feeler gauge.
    10. • The weight of the differential case against the rear axle housing causes the original light drag. The differential bearing preload causes the additional drag.
    • Start with a thin feeler gauge. This provides a sense of feel that is necessary in order to recognize the beginning of the preload and obtain zero clearance.
    • Work the differential case in, out, and to the left in order to insert the feeler gauge.
  10. Remove the following components from the rear axle housing:
    11. • The left side differential bearing cap
    • The left side bearing shim
  11. With no preload on the differential bearings, add the following measurements in order to obtain the size of the total shim pack :
    12. • The feeler gauge reading measured in Step 7.
    • The thickness of the bearing shims that were installed in Step 6.
  12. Select two bearing shims of approximately equal size. The total thickness of the two shims must be equal to the value obtained in Step 9.

    13. When installing the differential case into the rear axle housing, install the bearing shims between the following components:

    • Each differential bearing race
    • Each service bearing spacer
    • Add the additional preload after you install the differential case.
  13. When the drive pinion gear is in position, install the ring gear. Refer to Rear Axle Assemble .