Differential Bearing Preload and Gear Backlash

Fig. 38:

Differential side bearing preload and gear backlash is achieved by selective shims inserted between the bearing cup and the axle housing. The proper shim thickness can be determined using slip-fit Dummy Bearings 8398 in place of the differential side bearings and a dial indicator C-3339. Before proceeding with the differential bearing preload and gear backlash measurements, measure the pinion gear depth and prepare the pinion for installation. Establishing proper pinion gear depth is essential to establishing gear backlash and tooth contact patterns. After the overall shim thickness to take up differential side play is measured, the pinion is installed, and the gear backlash shim thickness is measured. The overall shim thickness is the total of the dial indicator reading, starting point shim thicknesses, and the preload specification added together. The gear backlash measurement determines the thickness of the shim used on the ring gear side of the differential case. Subtract the gear backlash shim thickness from the total overall shim thickness and select that amount for the pinion side of the differential (Fig. 38).

SHIM SELECTION

NOTE: It is difficult to salvage the differential side bearings during the removal procedure. Install replacement bearings if necessary.

1. Remove side bearings from differential case.
2. Install ring gear, if necessary, on differential case and tighten bolts to specification.
3. Install Dummy Side Bearings 8398 on differential case.
4. Install differential case in axle housing.

Fig. 39:

5. Insert Dummy Shims 8107 (0.118 in. (3.0 mm)) starting point shims between both dummy bearings and the axle housing (Fig. 39).
6. Install the marked bearing caps in their correct positions. Install and snug the bolts.

Fig. 40:

Fig. 41:

7. Using a dead-blow type mallet, seat the differential dummy bearings to each side of the axle housing (Fig. 40) and (Fig. 41).

Fig. 42:

8. Thread guide stud L-4438 into rear cover bolt hole below ring gear (Fig. 42).
9. Attach dial indicator C-3339 to guide stud. Position the dial indicator plunger on a flat surface on a ring gear bolt head (Fig. 42).

Fig. 43:

10. Push firmly and hold differential case to pinion side of axle housing (Fig. 43).
11. Zero dial indicator face to pointer.

Fig. 44:

12. Push firmly and hold differential case to ring gear side of the axle housing (Fig. 44).
13. Record dial indicator reading.
14. Add the dial indicator reading to the starting point shim thicknesses to determine the total shim thickness necessary to achieve zero differential end play.
15. Add 0.008 inch (0.2 mm) to the zero end play total. This new total represents the thickness of shims necessary to compress, or preload the new bearings when the differential is installed.
16. Rotate dial indicator out of the way on guide stud.
17. Remove differential case, dummy bearings, and starting point shims from the axle housing.
18. Install the pinion in the axle housing. Install the companion flange and establish the correct pinion rotating torque.
19. Install differential case and dummy bearings in axle housing with a single Dummy Shim 8107 on the ring gear side of the axle and tighten retaining cap bolts.

Fig. 46:

20. Position the dial indicator plunger on a flat surface between the ring gear bolt heads (Fig. 46).
21. Push and hold differential case toward pinion.
22. Zero dial indicator face to pointer.
23. Push and hold differential case to ring gear side of the axle housing.
24. Record dial indicator reading.
25. Subtract 0.002 inch (0.05 mm) from the dial indicator reading to compensate for backlash between ring and pinion gears. Add the resulting measurement to the thickness of the single starting point shim. This total is the thickness of shim required to achieve proper backlash.
26. Subtract the backlash shim thickness from the total preload shim thickness. The remainder is the shim thickness required on the pinion side of the axle housing.
27. Rotate dial indicator out of the way on guide stud.
28. Remove differential case, dummy bearings, and dummy shim from axle housing.
29. Install new side bearing cones and cups on differential case.
30. Install spreader W-129-B, utilizing Adapter Plates 8142-A, on axle housing and spread axle opening enough to receive differential case.
31. Place the side bearing shims in the axle housing against the axle housing shoulder.
32. Install the differential case in the axle housing.
33. Rotate the differential case several times to seat the side bearings.

Fig. 45:

34. Position the indicator plunger against a ring gear tooth (Fig. 45).
35. Push and hold ring gear upward while not allowing the pinion gear to rotate.
36. Zero dial indicator face to pointer.
37. Push and hold ring gear downward while not allowing the pinion gear to rotate. Dial indicator reading should be between 0.12 mm (0.005 inch) and 0.20 mm (0.008 inch). If backlash is not within specifications transfer the necessary amount of shim thickness from one side of the differential housing to the other (Fig. 46).
38. Verify differential case and ring gear runout by measuring ring to pinion gear backlash at eight locations around the ring gear. Readings should not vary more than 0.05 mm (0.002 inch). If readings vary more than specified, the ring gear or the differential case is defective.
After the proper backlash is achieved, perform the Gear Contact Pattern Analysis procedure.