Front Axle - 186FIA
PINION DEPTH-BEARING PRELOAD-GEAR BACKLASH
Ring and pinion gears are supplied as matched sets. Gear match numbers (3) for the ring and pinion gear are etched onto each gear. A plus (+) number, minus (-) number or zero (0) is etched into the face of 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 with a (0).
If installing a new gear, note the depth variance number of the original and replacement pinion. The numbers represent thousands of an inch deviation from the standard. Add or subtract this number from the original depth shim/oil slinger to compensate for the difference in the depth variances. 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.
Compensation for pinion depth variance is achieved with a select shim/oil slinger. The shims are placed between the rear pinion bearing and pinion gear head.
Pinion Gear Depth Variance Chart: Note where Old and New Pinion Marking columns intersect. Intersecting figure represents plus or minus the amount needed.
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-3339A (1).
1. Assemble Pinion Height Block 6739 (3), Pinion Block 8804 (6) and rear pinion bearing onto Screw 6741 (5).
2. Insert height gauge components into the housing through pinion bearing cups.
3. Install front pinion bearing and Cone-nut 6740 (4) onto the screw. Tighten Cone-Nut until Torque To Rotate screw is 1.7 Nm (15 in. lbs.).
4. Position Arbor Discs 6927A (1) and Arbor D-115-3 (2) into the housing bearing cradles.
5. Install differential bearing caps (1) on Arbor Discs and tighten bolts (2) to 61 Nm (45 ft. lbs.).
6. Assemble Dial Indicator C-3339A into Scooter Block D-115-2 and secure set screw.
7. Position Dial Indicator (1) with Scooter Block (2) flush on the pinion height block. Hold scooter block and zero the dial indicator.
8. Slowly slide the scooter block (2) across the pinion block over to the arbor (3). Move the scooter block till the dial indicator probe crests the arbor (3) and record the highest reading.
9. Select a shim equal to the dial indicator reading plus or minus the pinion depth variance number on the face of the pinion. For example: If the depth variance is -2, add 0.002 in. to the dial indicator reading. If the depth variance is +2, subtract 0.002 in. from the dial indicator reading.
DIFFERENTIAL SIDE BEARING PRELOAD AND GEAR BACKLASH
Differential bearing preload and gear backlash is achieved with selective shims (2) (4) located between the differential bearing cups and differential housing. Shim thickness is determined using Dummy Bearings D-348 and Dummy Shims 8107 in place of the differential side bearings and preload shims.
Before measuring differential bearing preload and gear backlash, pinion gear depth must be established and pinion gear prepared for installation. Pinion gear depth is essential to establishing gear backlash and tooth contact patterns.
PRELOAD SHIM SELECTION
1. Remove differential side bearings from differential case.
2. Install ring gear on differential case and tighten bolts to specification.
3. Install Dummy Bearings D-348 (1) on differential case.
4. Install differential case in the housing.
5. Record thickness of Dummy Shims 8107 (2) then install shims between dummy bearings and differential housing. NOTE: Each dummy shim is 3 mm (0.118 in.) thick.
6. Install bearing caps (1) in their correct positions and snug bearing cap bolts (3).
7. With a dead-blow hammer (1), seat differential dummy bearing to pinion side of the housing (2).
8. With a dead-blow hammer (2), seat differential dummy bearing to ring gear (3) side of the housing (1).
9. Thread Pilot Stud C-3288-B (2) into rear cover bolt hole below ring gear.
10. Attach a Dial Indicator C-3339A (3) to the Pilot Stud. Position the dial indicator plunger on flat surface between the ring gear bolts.
11. Push and hold differential case to pinion gear side (1) of the housing and zero dial indicator.
12. Push and hold differential case to ring gear side of the housing (2) and record dial indicator (1) reading.
13. Add dummy shims thickness 6 mm (0.236 in.) plus preload specification 0.152 mm (0.006 in.) to the dial indicator reading. This is the total shim thickness needed to preload the new bearings when the differential is installed.
EXAMPLE: Differential Dial Indicator Reading + Dummy Shims 6 mm (0.236 in.) + Preload Specification 0.152 mm (0.006 in.) = Total Differential Shim
14. Rotate dial indicator out of the way on the pilot stud.
15. Remove differential case and dummy bearings from the housing.
16. Install pinion gear in the housing. Install the pinion flange (1) and establish pinion torque to rotate with an inch pound torque wrench (2).
17. Install differential case and Dummy Bearings D-348 in the housing.
18. Install a single dummy shim in the ring gear side. Install bearing caps (1) and tighten bearing cap bolts (3) snug.
19. Seat ring gear side dummy bearing.
20. Position the dial indicator (1) plunger on a flat surface between the ring gear (3) bolt heads.
21. Push and hold differential case toward pinion gear (2) and zero dial indicator (1).
22. Push and hold differential case (2) to ring gear side (3) of the housing and record ring gear side dial indicator (1) reading. Add 3 mm (0.118 in.) one dummy shim thickness to ring gear side reading.
23. Subtract backlash specification 0.076 mm (0.003 in.) from total ring gear side reading for ring gear backlash. This is the shim needed on the ring gear side of the differential.
EXAMPLE: Ring Gear Side Dial Indicator Reading + One Dummy Shim 3 mm (0.118 in.) - Backlash Specification 0.076 mm (0.003 in.) = Ring Gear Side Shim
24. Subtract ring gear shim total from preload shim total thickness. The remainder is the shim thickness needed on the pinion side of the differential.
EXAMPLE : Total Differential Shim - Ring Gear Side Shim = Pinion Gear Side Shim
25. Rotate dial indicator out of the way on pilot stud.
26. Remove differential case and dummy bearings from the housing.
27. Install side bearings and cups on differential case.
28. Install Spreader Adapters 9959, Spreader W-129-B (1) and Spreader Retainers W-129-1 (2) on housing tighten spreader turnbuckle finger-tight.
29. Attach Dial Indicator C-3339A to spreader retainer stud. Load indicator plunger against opposite side of the housing and zero the indicator
30. Spread the differential case 0.34 mm (0.013 in). CAUTION: Never spread the differential housing over 0.34 mm (0.013 in). Failure to follow these instruction could result in distorting the housing.
31. Install differential case with shims.
GEAR BACKLASH
1. Rotate the differential case several times to seat the side bearings.
2. Position the indicator plunger (1) against a ring gear tooth (2).
3. Push and hold ring gear upward while not allowing the pinion gear to rotate.
4. Zero dial indicator face to pointer.
5. Push and hold ring gear downward while not allowing the pinion gear to rotate. Dial indicator reading (backlash ) should be between 0.12 - 0.20 mm (0.005 - 0.008 in.).
NOTE: If backlash is not within specifications, transfer the necessary shim thickness from one side of the housing to the other.
6. 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 Analysis 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.
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.
NOTE: If the PROFILE across the tooth is the same, it is a Three Axis cut gear. If the PROFILE across the tooth is tapered, it is a Two Axis cut gear.
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 and adjust pinion depth and gear backlash as necessary.
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:
- Gear Ratio 3.21: 0.34 - 1.24 Nm (3 - 10.9 in. lbs.)
- Gear Ratio 3.73: 0.45 - 0.75 Nm (3.9 - 6.6 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.