Rear Axle - 8 1/4: Adjustments

ADJUSTMENTS





Ring gears and pinions are supplied as matched sets only. The identifying numbers for the ring gear and pinion are etched into the face of each gear (Fig. 5). A plus (+) number, minus (-) number or zero (0) is etched into the face of the pinion. This number is the amount (in thousandths of an inch) the depth varies from the standard depth setting of a pinion etched with a (0). The standard depth provides the best gear tooth contact pattern. Refer to Backlash and Contact Pattern Analysis.





Compensation for pinion depth variance is achieved with select shims. The shims are placed behind the rear pinion bearing (Fig. 6).
If a new gear set is being installed' note the depth variance etched into both the original and replacement pinion. Add or subtract the thickness of the original depth shims to compensate for the difference in the depth variances. Refer to the Depth Variance chart.
Note where Old and New Pinion Marking columns intersect. Intersecting figure represents plus or minus the amount needed.
Note the etched number on the face of the pinion gear head (-1, -2, 0, +1, +2, etc.). The numbers represent thousands of an inch deviation from the standard. If the number is negative, add that value to the required thickness of the depth shims. If the number is positive, subtract that value from the thickness of the depth shim. If the number is O no change is necessary.





PINION GEAR DEPTH VARIANCE

PINION DEPTH MEASUREMENT
Measurements are taken with pinion bearing cups and pinion bearings installed in the housing. Take measurements with Pinion Gauge Set and Dial Indicator C-3339.





1. Assemble Pinion Height Block 6739, Pinion Block 8540 and rear pinion bearing onto Screw 6741 (Fig. 7).





2. Insert assembled height gauge components, rear bearing, and screw into the housing through pinion bearing cups (Fig. 8).
3. Install front pinion bearing and Cone-Nut 6740 hand tight (Fig. 7).





4. Place Arbor Disc 8541 on Arbor D-115-3 in position in the housing side bearing cradles (Fig. 9). Install differential bearing caps on Arbor Discs and tighten cap bolts to 41 Nm (30 ft. lbs.).

NOTE: Arbor Discs 8541 has different step diameters to fit other axles. Choose proper step for axle bear' serviced.

5. Assemble Dial Indicator C-3339 into Scooter Block D-115-2 and secure set screw.
6. Place Scooter Block/Dial Indicator in position in axle housing so dial probe and scooter block are flush against the rearward surface of the pinion height block (Fig. 7). Hold scooter block in place and zero the dial indicator. Tighten dial indicator face lock screw.
7. Slowly slide the dial indicator probe over the edge of the pinion height block.





8. Slide the dial indicator probe across the gap between the pinion height block and the arbor bar with the scooter block against the pinion height block (Fig. 10). When the dial probe contacts the arbor bar, the dial pointer will turn clockwise. Continue moving the dial probe to the crest of the arbor bar and record the highest reading. If the dial indicator can not achieve the zero reading, the rear bearing cup or the pinion depth gauge set is not installed correctly.
9. Select a shim equal to the dial indicator reading plus the drive pinion gear depth variance number etched in the face of the pinion (Fig. 5). For example, if the depth variance is -2, add +0.002 inch to the dial indicator reading.

BEARING PRELOAD AND GEAR BACKLASH
The following must be considered when adjusting bearing preload and gear backlash:
^ The maximum ring gear backlash variation is 0.003 inch (0.076 mm).
^ Mark the gears so the same teeth are meshed during all backlash measurements.
^ Maintain the torque while adjusting the bearing preload and ring gear backlash.
^ Excessive adjuster torque will introduce a high bearing load and cause premature bearing failure. Insufficient adjuster torque can result in excessive differential case free-play and ring gear noise.
^ Insufficient adjuster torque will not support the ring gear correctly and can cause excessive differential case free-play and ring gear noise.

NOTE: The differential bearing cups will not always immediately follow the threaded adjusters as they are moved during adjustment. To ensure accurate bearing cup responses to the adjustments:

^ Maintain the gear teeth engaged (meshed) as marked.
^ The bearings must be seated by rapidly rotating the pinion gear a half turn back and forth.
^ Do this five to ten times each time the threaded adjusters are adjusted.





1. Use Wrench C-4164 to adjust each threaded adjuster inward until the differential bearing freeplay is eliminated (Fig. 11). Allow some ring gear backlash (approximately 0.01 inch/0.25 mm) between the ring and pinion gear. Seat the bearing cups with the procedure described above.





2. Install dial indicator and position the plunger against the drive side of a ring gear tooth (Fig. 12). Measure the backlash at 4 positions (90 degrees apart) around the ring gear. Locate and mark the area of minimum backlash.
3. Rotate the ring gear to the position of the least backlash. Mark the gear so that all future backlash measurements will be taken with the same gear teeth meshed.
4. Loosen the right-side, tighten the left-side threaded adjuster. Obtain backlash of 0.003 to 0.004 inch (0.076 to 0.102 mm) with each adjuster tightened to 14 Nm (10 ft. lbs.). Seat the bearing cups with the procedure described above.
5. Tighten the differential bearing cap bolts 95 Nm (70 ft. lbs.).
6. Tighten the right-side threaded adjuster to 102 Nm (75 ft. lbs.). Seat the bearing cups with the procedure described above. Continue to tighten the right-side adjuster and seat bearing cups until the torque remains constant at 102 Nm (75 ft. lbs.)
7. Measure the ring gear backlash. The range of backlash is 0.006 to 0.008 inch (0.15 to 0.203 mm).
8. Continue increasing the torque at the right side threaded adjuster until the specified backlash is obtained.

NOTE: The left-side threaded adjuster torque should have approximately 102 Nm (75 ft. lbs.). If the torque is considerably less, the complete adjustment procedure must be repeated.

9. Tighten the left-side threaded adjuster until 102 Nm (75 ft. lbs.) torque is indicated. Seat the bearing rollers with the procedure described above. Do this until the torque remains constant.
10. Install the threaded adjuster locks and tighten the lock screws to 10 Nm (90 inch lbs.).
After the proper backlash is achieved, perform the Gear Contact Pattern procedure.

GEAR CONTACT PATTERN
The ring gear and pinion teeth contact patterns will show if the pinion depth is correct in the housing. It will also show if the ring gear backlash has been adjusted correctly. The backlash can be adjusted within specifications to achieve desired tooth contact patterns.

1. Apply a thin coat of hydrated ferric oxide or equivalent, to the drive and coast side of the ring gear teeth.
2. Wrap, twist and hold a shop towel around the pinion yoke to increase the turning resistance of the pinion. This will provide a more distinct contact pattern.
3. With a boxed end wrench on a ring gear bolt, rotate the differential case one complete revolution in both directions while a load is being applied from shop towel.





The areas on the ring gear teeth with the greatest degree of contact against the pinion teeth will squeegee the compound to the areas with the least amount of contact. Note and compare patterns on the ring gear teeth to Gear Tooth Contact Patterns chart (Fig. 13) and adjust pinion depth and gear backlash as necessary.

SIDE GEAR CLEARANCE
When measuring side gear clearance, check each gear independently. If it necessary to replace a side gear, replace both gears as a matched set.

1. Install the axle shafts and C-locks and pinion mate shaft.





2. Measure each side gear clearance. Insert a matched pair of feeler gauge blades between the gear and differential housing on opposite sides of the hub (Fig. 14).
3. If side gear clearances is no more than 0.005 inch. Determine if the axle shaft is contacting the pinion mate shaft. Do not remove the feeler gauges, inspect the axle shaft with the feeler gauge inserted behind the side gear. If the end of the axle shaft is not contacting the pinion mate shaft, the side gear clearance is acceptable.





4. If clearance is more than 0.005 inch (axle shaft not contacting mate shaft), record the side gear clearance. Remove the thrust washer and measure its thickness with a micrometer. Add the washer thickness to the recorded side gear clearance. The sum of gear clearance and washer thickness will determine required thickness of replacement thrust washer (Fig. 15). In some cases, the end of the axle shaft will move and contact the mate shaft when the feeler gauge is inserted. The C-lock is preventing the side gear from sliding on the axle shaft.
5. If there is no side gear clearance, remove the C-lock from the axle shaft. Use a micrometer to measure the thrust washer thickness. Record the thickness and re-install the thrust washer. Assemble the differential case without the C-lock installed and remeasure the side gear clearance.
6. Compare both clearance measurements. If the difference is less than 0.012 inch (0.305 mm), add clearance recorded when the C-lock was installed to thrust washer thickness measured. The sum will determine the required thickness of the replacement thrust washer.
7. If clearance is 0.012 inch (0.305 mm) or greater, both side gears must be replaced (matched set) and the clearance measurements repeated.
8. If clearance (above) continues to be 0.012 inch (0.305 mm) or greater, the case must be replaced.