Front Axle - 186FIA: Adjustments
FRONT AXLE - 186FIAADJUSTMENTS
Ring and pinion gears are supplied as matched sets. Gear match numbers (3) (Fig. 14) for the ring and pinion gear are etched onto each gear. A plus (+) number, minus (-) number or zero (O) 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 (O).
Compensation for pinion depth variance is achieved with a select shim/oil slinger. The shims are placed between the rear pinion bearing and the pinion gear head.
If installing a new gear, note the depth variance number of the original and replacement pinion. Add or subtract this number from the original depth shim/oil slinger to compensate for the difference in the depth variances. 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.
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-3339 (1) (Fig. 15).
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 inch lbs.).
4. Position Arbor Disc 6732 (2) (Fig. 16) and Arbor D-115-3 (3) into the housing bearing cradles. Install differential bearing caps on Arbor Discs and tighten 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. Position Scooter Block (1) (Fig. 17) with Dial Indicator (3) flush on the pinion height block. Hold the scooter block and zero the dial indicator.
7. Slowly slide the scooter block across the pinion height block over to the arbor (2). Move the scooter block till the dial indicator probe crests the arbor (2) and record the highest reading.
8. Select a shim/oil slinger equal to the dial indicator reading plus the pinion depth variance number etched in the face of the pinion. 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 bearing preload and gear backlash is achieved with selective shims (2) (4) (Fig. 18) located between the differential bearing cups and differential housing. 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 measuring differential bearing preload and gear backlash, measure pinion gear depth and prepare pinion for installation. Pinion gear depth is essential to establishing gear backlash and tooth contact patterns. After measuring shim thickness to take up differential side play, install pinion and measure gear backlash shim thickness. Overall shim thickness is the dial indicator reading and preload specification added together. The gear backlash measurement determines the shim thickness used on the ring gear side of the differential case. Subtract gear backlash shim thickness from overall shim thickness to determine shim thickness for pinion gear side of the differential. 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. Install ring gear on differential case and tighten bolts to specification.
3. Install Dummy Bearings D-348 (4) (Fig. 19) on differential case (3).
4. Install differential case in the housing.
5. Record the thickness of Dummy Shims 8107 (1). Insert the shims between the dummy bearings and the differential housing (2).
6. Install the bearing caps (1) (Fig. 20) in their correct positions and snug the bolts (3).
7. With a dead-blow hammer (1) (Fig. 21), seat the differential dummy bearings to pinion side of the housing (2).
8. With a dead-blow hammer (2) (Fig. 22), seat the differential dummy bearings to the ring gear (3) side of the housing (1).
9. Thread Pilot Stud C-3288-B (2) (Fig. 23) into rear cover bolt hole below ring gear.
10. Attach a Dial Indicator C-3339 (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) (Fig. 24) and record dial indicator (1) reading.
13. Add 0.152 mm (0.006 inch) 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.
14. Rotate dial indicator out of the way on the pilot stud.
15. Remove differential case and dummy bearings from the housing.
16. Install the pinion gear in the housing. Install the pinion yoke and establish the correct pinion rotating torque.
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 cans and tighten bolts snug.
19. Seat ring gear side dummy bearing.
20. Position the dial indicator (1) (Fig. 25) 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.
22. Push and hold differential case to ring gear side (3) (Fig. 26) of the housing and record dial indicator (1) reading. Add dummy shim thickness to this reading. This will be the total shim thickness to achieve zero backlash.
23. Subtract 0.076 mm (0.003 inch) 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.
24. Subtract the backlash shim thickness from the total preload shim thickness. The remainder is the shim thickness required on the pinion side of the axle housing.
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 W-129-B with Adapter Set 6987 on the housing and spread axle opening enough to receive differential case.
CAUTION: Never spread the differential housing over 0.34 mm (0.013 inch). If the housing is overspread, it could be distorted or damaged.
29. Place the bearing preload shims in the axle housing, against the axle tubes.
30. Install differential case into the housing.
31. Remove spreader from the housing.
GEAR BACKLASH
1. Rotate the differential case several times to seat the side bearings.
2. Position the indicator plunger (1) (Fig. 27) 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 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.
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 inch). If readings vary more than specified, the ring gear or the differential case is defective.
After the proper backlash (Fig. 28) 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) (Fig. 29) 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 3 Axis cut gear. If the PROFILE across the tooth is tapered it is a 2 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 (Fig. 30) 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 (1) (Fig. 31) and differential combined with an inch pound torque wrench (2). This will verify the correct differential bearing preload.
Torque to rotate the differential and pinion is the torque to rotate the pinion plus:
^ Gear Ratio 3.55 - 0.48 - 0.78 Nm (4.2 - 6.9 inch lbs.)
^ Gear Ratio 3.73 - 0.45 - 0.75 Nm (3.9 - 6.6 inch lbs.)
^ Gear Ratio 4.10 - 0.41 - 0.69 Nm (3.6 - 6.0 inch lbs.)