Front Axle - 186FBI
PINION DEPTH-BEARING PRELOAD-GEAR BACKLASH
For special tools, refer to Tools and Equipment
Compensation for pinion depth variance is achieved with a select shim (1). The shims are placed between the rear pinion bearing and the pinion gear head. A collapsible spacer on the pinion shaft is used to maintained pinion bearing preload. Differential bearing preload and ring gear (3) backlash is achieved, with select shims (2,4) located behind the bearing cups.
Ring and pinion gears are supplied as matched sets. The identifying numbers (3) for the ring and pinion gear are etched/marked onto each gear. A plus (+) number, minus (-) number or zero (0) is etched/marked on the pinion gear (2). This number is the amount (in thousandths of an inch) the depth varies from the standard depth setting of a pinion etched/marked with a (0).
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 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 0 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 Dial Indicator C-3339A (1).
1. Assemble Pinion Height Block 6739 (2), Pinion Block 9946 (1) and rear pinion bearing onto Screw 6741.
2. Insert assembled height gauge components into the housing through pinion bearing cups.
3. Install front pinion bearing and Cone-nut 6740. Tighten nut until torque to rotate the screw is 2.25 Nm (20 in. lbs.).
4. Place Arbor Disc 6732 (1) on Arbor D-115-3 (2) and position in axle housing differential bearing cradles. NOTE: Arbor Discs 6732 has different step diameters to fit other axles. Choose proper step for axle being serviced.
5. Install differential bearing caps (1) on arbor discs (2) and tighten cap bolts to 61 Nm (45 ft. lbs.).
6. Install Dial Indicator C-3339A (1) into Scooter Block D-115-2A (2) and secure set screw.
7. Position Scooter Block/Dial Indicator flush on the pinion height block and zero the dial indicator.
8. Slowly slide the scooter block across the pinion height block over to the arbor. Move the scooter block till the dial indicator probe crests the arbor and record the highest reading.
9. Select a shim equal to the dial indicator reading plus or minus the pinion depth variance number etched in the face of the pinion. Example: If depth variance is -2 add 0.002 in. to the dial indicator reading. If depth variance is +2 subtract 0.002 in. from the dial indicator reading. The total is the shim thickness needed for the pinion depth variance.
DIFFERENTIAL BEARING PRELOAD AND GEAR BACKLASH
Before performing differential bearing preload and ring gear backlash measurements, pinion gear depth must be established and the pinion gear ready for installation. Establishing pinion gear depth is essential to ring gear backlash and tooth contact patterns.
Differential side bearing preload and gear backlash is accomplish with selective shims (2,4) positioned behind the differential side bearing cups. Shims are determined using Dummy Bearings D-348 in place of the differential side bearings and a Dial Indicator C-3339A.
SHIM FORMULA: Differential End Play + Preload Specification = Total Differential Shim. Total Differential Shim - Ring Gear Side Shim - Backlash Specification = Pinon Gear Side Shim.
PRELOAD SHIM SELECTION
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 (1) on differential case (3) and install differential case (3) in the housing (2).
5. Install differential (3) bearing caps (1) in original location and snug bearing cap bolts.
6. Seat differential dummy bearings to pinion gear side of the housing (2), with a dead-blow hammer (1).
7. Seat differential dummy bearings to ring gear side of the housing (1), with a dead-blow hammer (2).
8. Thread Pin C-3288-B (2) into cover bolt hole.
9. Attach Dial Indicator C-3339A (1) to the pin and position indicator plunger on a flat surface between the ring gear bolts.
10. Push and hold differential case (1) to pinion gear side of the housing and zero dial indicator (2).
11. Push and hold differential case (2) to ring gear side of the housing. Record the dial indicator (1) reading. Add preload specification 0.2 mm (0.008 in.) to differential dial indicator reading. This is the total differential shim thickness needed to preload the differential bearings.
EXAMPLE: Differential Dial Indication Reading + Preload Specification 0.2 mm (0.008 in.) = Total Differential Shim
12. Rotate dial indicator out of the way on the pilot stud.
13. Remove differential case and dummy bearings from the housing.
14. Install pinion gear in the housing and establish pinion (1) torque to rotating (PTTR).
15. Install differential case (1) with dummy bearings D-348 in the housing, install bearing caps and snug bolts.
16. Seat ring gear side dummy bearing.
17. Position dial indicator (2) plunger on a flat surface between the ring gear bolts.
18. Push and hold differential case (1) against pinion gear and zero dial indicator (2).
19. Push and hold differential case (2) to ring gear side of the housing and record dial indicator (1) ring gear side reading.
20. Subtract backlash specification 0.05 mm (0.002 in.) from ring gear side reading for ring gear backlash. The remainder is the shim needed on the ring gear side of the differential.
EXAMPLE: Ring Gear Side Reading - Backlash Specification 0.05 mm (0.002 in.) = Ring Gear Side Shim
21. Subtract ring gear side shim from differential total preload shim. The remainder is the shim needed on the pinion gear side of the differential.
EXAMPLE: Total Differential Shim - Ring Gear Side Shim = Pinion Gear Side Shim
22. Rotate dial indicator out of the way on pilot stud.
23. Remove differential case with dummy bearings from the housing.
24. Install side bearings on differential case.
25. Install spreader W-129-B (1) and hold down adapters (2) from Adapter Set 6987B onto housing. Spread the housing 0.50 mm (0.020 in.). CAUTION: Never spread housing over 0.50 mm (0.020 in.). Failure to follow these instruction could result in distorting the housing.
26. Install differential case (2) with bearings cups (3) and shims into the housing (1).
27. Remove spreader from the housing.
28. Install bearing caps (1) and tighten bolts to 61 Nm (45 ft. lbs.).
29. Rotate differential case several times to seat the side bearings.
30. Position dial indicator plunger (1) against a ring gear tooth.
31. Push and hold ring gear upward while holding the pinion gear.
32. Zero dial indicator face to pointer.
33. Push and hold ring gear downward while holding the pinion gear. Dial indicator reading should be between 0.12 mm - 0.20 mm (0.005 in - 0.008 in). If backlash is not within specifications transfer the necessary amount of shim thickness from one side of the housing to the other.
34. 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 in). 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 gear and pinion teeth contact patterns will show if the pinion gear depth and ring gear backlash has been adjusted correctly. Backlash can be adjusted within specifications to achieve desired tooth contact patterns.
The TOP LAND (1) of the gear tooth is the top surface of the tooth. The PROFILE (2) of the gear tooth is the depth of the tooth. The TOE (3) of the gear is the portion of the tooth surface at the end towards the center. The HEEL (4) of the gear is the portion of the tooth at the outer-end. The ROOT (5) of the gear tooth is the lowest portion of the tooth.
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 flange 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 loading the pinion gear with shop towel.
The ring gear teeth with the greatest degree of contact with the pinion gear 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 and adjust pinion depth and gear backlash as necessary.
NOTE: If the PROFILE across the tooth is the same it is a 3 Axis cut gear. If the PROFILE across the tooth is tapered it is a 2 Axis cut gear.
3 AXIS CUT GEAR
2 AXIS CUT GEAR
DIFFERENTIAL BEARING PRELOAD CHECK
With an inch pound torque wrench (2) measure Total Torque To Rotate (TTTR). This is the final check on the differential assembly before installing the axle shafts. This will verify the correct differential bearing preload.
Total Torque To Rotate is: Pinion Torque To Rotate (PTTR) plus 0.79 - 1.24 Nm (7 - 11 in. lbs.).
NOTE: If TTTR is high, decrease the shim thickness equally on both sides of the differential and check TTTR again. If TTTR is low, increase the shims thickness equally on both sides of the differential and check TTTR again.