Front Axle - 186FBI: Adjustments

ADJUSTMENTS





Ring and pinion gears are supplied as matched sets only. The identifying numbers for the ring and pinion gear are etched into the face of each gear (Fig. 3). A plus (+) number, minus (-) number or zero (0) is etched into the face of the pinion gear. 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 setting from the center line of the ring gear to the back face of the pinion is 92.08 mm (3.625 inch). The standard depth provides the best gear tooth contact pattern.





Compensation for pinion depth variance is achieved with a select shim/oil baffle. The shims are placed between the rear pinion bearing and the pinion gear head (Fig. 4).
If a new gear set is being installed, note the depth variance etched into both the original and replacement pinion. Add or subtract this number from the thickness of the original depth shim/oil slinger to compensate for the difference in the depth variances. Refer to the Pinion Gear 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 AND ADJUSTMENT





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 (Fig. 5).

1. Assemble Pinion Height Block 6739, Pinion Block 6733 and rear pinion bearing onto Screw 6741 (Fig. 5).





2. Insert assembled height gauge components, rear bearing and screw into the housing through pinion bearing cups (Fig. 6).
3. Install front pinion bearing and Cone-nut 6740 hand tight (Fig. 5).





4. Place Arbor Disc 6732 on Arbor D-115-3 in position in axle housing side bearing cradles (Fig. 7). Install differential bearing caps on arbor discs and tighten cap bolts to 41 Nm (30 ft. lbs.).

NOTE: Arbor Discs 6732 has different step diameters to fit other axles. Choose proper step for axle being 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 the housing so dial probe and scooter block are flush against the rearward surface of the pinion height block (Fig. 5). Hold scooter block in place and zero the dial indicator face to the pointer. Tighten dial indicator face lock screw.
7. With scooter block still in position against the pinion height block, 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. 8). When the dial probe contacts the arbor bar, the dial pointer will turn clockwise. Bring dial pointer back to zero against the arbor bar, do not turn dial face. 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/oil baffle equal to the dial indicator reading plus the pinion depth variance number etched in the face of the pinion (Fig. 3). For example, if the depth variance is -2, add +0.002 inch to the dial indicator reading.

DIFFERENTIAL SIDE BEARING PRELOAD AND GEAR BACKLASH





Differential side bearing preload and gear backlash is achieved by selective shims positioned behind the differential side bearing cones. The proper shim thickness can be determined using slip-fit Dummy Bearings D-348 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 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 gear side of the differential (Fig. 9). Differential shim measurements are performed with spreader W-129-B removed.

PRELOAD SHIM SELECTION

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

1. Remove differential side bearings from differential case.
2. Remove factory installed shims from differential case.
3. Install ring gear on differential case and tighten bolts to specification.
4. Install dummy side bearings D-348 on differential case.
5. Install differential case in the housing.





6. Install the marked bearing caps in their correct positions. Install and snug the bolts (Fig. 10).








7. Using a dead-blow hammer, seat the differential dummy bearings to each side of the housing (Fig. 11) and (Fig. 12).





8. Thread Pilot Stud C-3288-B into rear cover bolt hole below ring gear (Fig. 13).
9. Attach the Dial Indicator C-3339 to pilot stud. Position the dial indicator plunger on a flat surface between the ring gear bolt heads (Fig. 13).





10. Push and hold differential case to pinion gear side of the housing and zero dial indicator (Fig. 14).





11. Push and hold differential case to ring gear side of the housing and record the dial indicator reading (Fig. 15).
12. Add 0.008 inch (0.2 mm) to the zero end play total. This new total represents the thickness of shims to compress or preload the new bearings when the differential is installed.
13. Rotate dial indicator out of the way on the pilot stud.
14. Remove differential case and dummy bearings from the housing.
15. Install the pinion gear in the housing. Install the pinion yoke and establish the correct pinion rotating torque.
16. Install differential case and dummy bearings D-348 in the housing (without shims), install bearing caps and tighten bolts snug.
17. Seat ring gear side dummy bearing (Fig. 12).
18. Position the dial indicator plunger on a flat surface between the ring gear bolt heads (Fig. 13).





19. Push and hold differential case toward pinion gear and zero the dial indicator (Fig. 16).





20. Push and hold differential case to ring gear side of the housing and record dial indicator reading (Fig. 17).
21. Subtract 0.002 inch (0.05 mm) from the dial indicator reading to compensate for backlash between ring and pinion gears. This total is the thickness shim required to achieve proper backlash.
22. Subtract the backlash shim thickness from the total preload shim thickness. The remainder is the shim thickness required on the pinion side of the housing.
23. Rotate dial indicator out of the way on pilot stud.
24. Remove differential case and dummy bearings from the housing.
25. Install the selected side bearing shims onto the differential case hubs.
26. Install side bearings and cups on differential case.
27. Install spreader W-129-B, utilizing some items from Adapter Set 6987, on the housing and spread open enough to receive differential case.
28. Install differential case into the housing.
29. Remove spreader from the housing.
30. Rotate the differential case several times to seat the side bearings.





31. Position the indicator plunger against a ring gear tooth (Fig. 18).
32. Push and hold ring gear upward while not allowing the pinion gear to rotate.
33. Zero dial indicator face to pointer.





34. 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 housing to the other (Fig. 19).
35. 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 Gear Contact Pattern procedure.

GEAR CONTACT PATTERN
The ring and pinion gear contact patterns will show if the pinion depth is correct. 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 the 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 squeeze 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. 20) and adjust pinion depth and gear backlash as necessary.

DIFFERENTIAL BEARING PRELOAD CHECK
The final check on the differential assembly before installing the axles is torque to rotate pinion and differential combined. This will verify the correct differential bearing preload.
Torque to rotate the differential and pinion should be the torque to rotate the pinion plus 0.79 - 1.24 Nm (7 - 11 inch lbs.).