Assembly & Adjustment

Fig. 2 Differential case & drive pinion assembly exploded view:

Differential Case
Lubricate components with specified differential lubricant prior to assembly. If components are to be reused, install them in original positions.
1. Position output shaft retaining rings in grooves of side gears, then install side gear thrust washers and side gears in case, Fig. 2.
2. Position differential pinions along with thrust washers in case, with pinions 180° apart and meshed with side gears.
3. Rotate gears until pinion gear bores are aligned with pinion shaft bores in case.
4. Insert pinion shaft, ensuring that retaining pin holes are aligned with holes in case, then secure shaft with new roll pin.
5. Ensure that ring gear mounting flange is clean and free from burrs, align bolt holes in ring gear with holes in case, then install ring gear bolts hand tight. Do not reuse ring gear bolts. If bottom surface of replacement bolt head is not serrated, apply suitable thread locking compound to bolt heads. If head is serrated, no locking compound is needed.
6. Torque ring gear bolts in progressive stages to 96 ft. lbs. Torque bolts alternately and evenly to avoid cocking ring gear.
7. Install differential case side bearings using a suitable driver.

Fig. 6 Pinion depth gauge installation:

Final Drive Housing
1. Lubricate inner pinion bearing race with specified differential lubricant, then install race in housing using a suitable driver. Inner bearing race acts as a stop for the pinion seal installation tool. If race is not fully seated, the seal will be mispositioned and may leak.
2. Lubricate outer pinion bearing race with automatic transmission fluid, then install race using a suitable driver. If ring gear and pinion assembly are being replaced, use following procedure to select pinion depth adjusting shim. If ring gear and pinion are being reused, proceed to step 9.
3. Lubricate inner pinion bearing with differential lubricant and outer bearing with automatic transmission fluid, then install bearings in housing.
4. Install pinion setting gauge J-21777-75 or equivalent and suitable dial indicator as follows:
a. Install pilot J-21777-8 on short threaded end of stud, Fig. 6, until seated, then install gauge plate and tighten plate against pilot.
b. Insert stud through bearings from inside of housing, then install outer bearing pilot J-21777-78.
c. Install hex nut on stud hand tight, rotate tool assembly to ensure that bearings are seated, then tighten nut until 20 inch lbs. of torque are needed to rotate bearings.
d. Mount side bearing discs on arbor and install assembly into housing, ensuring that smaller steps of discs are seated in side bearing webs, Fig. 6.
e. Install side bearing caps and torque bolts to 41 ft. lbs.
f. Install dial indicator on mounting post of arbor with contact button bearing against top of plunger, Fig. 6.
g. Preload indicator approximately 1/2 turn, then tighten mounting screw.
5. Rotate gauge until plunger rests squarely on flattest surface.
6. Rock arbor assembly back and forth across plate slowly until dial indicator registers largest deflection, then zero indicator.
7. Repeat step 6 several times to confirm setting. Once zero reading is set, swing plunger until it moves off gauge plate.
8. Dial indicator should read between .020 and .050 inch. Indicator reading corresponds to the required pinion depth adjusting shim thickness. Check inner face of drive pinion for a pinion code stamping. This number indicates a necessary change in pinion shim thickness in one-thousandths of an inch. If the number is proceeded by a plus, add the stamped value to the dimension obtained in step 8. If the number is followed by a minus, subtract the stamped value from the dimension obtained in step 8.
9. Install selected shim on pinion, then press on inner bearing.
10. Install pinion seal in housing using driver J-28516, ensuring seal is properly located in housing bore, then lubricate seal lips with automatic transmission fluid.
11. Lubricate inner pinion bearing with differential lubricant, install seal protector over end of pinion shaft, then insert pinion into housing.
12. Lubricate outer pinion bearing with automatic transmission fluid, then install new collapsible spacer and outer bearing on pinion shaft. Do not allow pinion to unseat from inner bearing race as seal may be damaged.

Fig. 3 Pinion bearing preload check:

13. Install pinion nut and tighten with a suitable wrench until all endplay has been eliminated, holding pinion shaft with spline adapter J-26514 or equivalent.
14. Check pinion bearing preload using a suitable torque wrench and spline adapter, Fig. 3, tightening pinion nut in small increments until specified preload is obtained. Rotate pinion several revolutions each time nut is tightened to ensure that bearings are properly seated.

Fig. 1 Final drive assembly exploded view:

Backlash & Side Bearing Preload Adjustment & Final Assembly
Do not re-use cast iron shims used during production as they may break when tapped into place. Measure thickness of left and right production shims or service spacer/shim pack assemblies, Fig. 1, to determine approximate thickness of shims required for differential case installation.
1. Install races on differential case side bearings, position case assembly in housing, then place a service spacer between each bearing race and housing.
2. Select and install one or two shims between left (opposite ring gear) bearing race and service spacer, filling gap until right (ring gear side) bearing race and spacer are snug against housing.

Fig. 7 Side bearing adjusting shim measurement:

Fig. 8 Ring gear & pinion backlash measurement:

3. Insert progressively larger feeler gauges between shim and service spacer until there is a noticeable increase in drag, Fig. 7. Original light drag is caused by weight of case against housing, while additional drag is caused by side bearing preload. By starting with smaller gauges, a sense of ``feel'' is obtained so that the beginning of preload can be recognized to obtain zero preload. Total shim thickness needed to obtain zero preload is equal to the thickness of feeler gauge used just before noticeable drag is felt plus the thickness of shims installed in step 2.
4. Remove shims installed in step 2.
5. Select two shims, as close to equal thickness as possible, that together equal the thickness of shims installed in step 2 plus the thickness of feeler gauge used to obtain zero preload.
6. Install one selected shim on each side between bearing race and service spacer to obtain zero preload ``slip fit'' of case assembly in housing.
7. Rotate differential case several revolutions to seat bearings, then mount suitable dial indicator on housing with button bearing against heel end of ring gear tooth, Fig. 8.
8. Check ring gear and pinion backlash at several positions, holding pinion while rocking gear back and forth, and record readings. If a variation greater than 0.002 inch is recorded, check for burred gears, improperly installed ring gear or distorted differential case, and correct as needed.
9. Install side bearing caps, torque bolts to 52 ft. lbs. and repeat step 8.
10. Backlash for new gears should be 0.005---0.009 inch, while backlash for used gears should be set to value recorded prior to disassembly.
11. If backlash is not within specifications, correct by increasing thickness of one side bearing shim while decreasing thickness of opposite shim by an equal amount to maintain proper side bearing preload. For each 0.002 inch change in shim thickness, backlash will be altered by 0.001 inch.
12. When backlash has been adjusted to specified value, remove side bearing caps and both shim packs, keeping components in order.

Fig. 9 Side bearing shim installation:

Fig. 10 Ring gear & pinion tooth contact inspection:

13. Adjust differential case side bearing preload as follows:
a. Select shim 0.003 inch larger than shim removed from right (ring gear) side, then install shim between right bearing race and spacer.
b. Install right bearing cap with bolts hand tight.
c. Select shim 0.003 inch larger than shim removed from left (opposite ring gear) side, then install shim between left bearing race and spacer, Fig. 9.
14. Install left bearing cap, then torque left and right cap bolts to 52 ft. lbs.
15. Ensure that backlash is still within specifications, then check tooth contact pattern using suitable gear marking compound.
16. If tooth contact is incorrect, Fig. 10, readjust pinion depth or backlash as needed.
17. When assembly adjustments have been properly completed, install output shaft seals, rear cover gasket and the cover.