8.6 Inch Axle

Backlash Adjustment (8.6 Inch Axle)

Tools Required
^ J8001 Dial Indicator Set
^ J25025 Guide Pins
^ J25588 Side Bearing Shim Installer





1. Install the J25025-1 and the J8001 to the axle housing as shown.
2. Place the indicator stem of the J8001-3 at the heel end of a gear tooth.
3. Set the J8001-3 so that the stem is aligned with the gear rotation and perpendicular to the tooth angle.
4. Preload the dial of the J8001-3. Align the needle and the dial face of the J8001-3 to ZERO.
5. While holding the drive pinion stationary, move the ring gear back and forth. Measure and record the backlash.
6. Repeat the measuring procedure at eight points around the ring gear.
The difference between the backlash at all of the measuring points should not vary by more than 0.05 mm (0.002 inch).
7. If the difference between the backlash at all of the measuring points varies by more than 0.05 mm (0.002 inch), inspect for the following conditions:
^ Burrs
^ A distorted case flange
^ Uneven bolting

8. If the difference between all the measuring points is within specifications, the backlash at the minimum lash point measured should be:
The backlash between the ring gear and the drive pinion should be between 0.08 - 0.25 mm (0.003 - 0.010 inch) with a preferred backlash of 0.13 - 0.18 mm (0.005 - 0.007 inch).

Important:
^ Do not use the original cast iron production shims to adjust the backlash. Use service shims and spacers instead.
^ Adjust the thickness of the shim pack on each side of the differential in equal amounts. This will maintain the correct differential side bearing preload.
^ Moving 0.05 mm (0.002 inch) of shim thickness from one side of the differential to the other will change the backlash adjustment approximately 0.03 mm (0.001 inch).

9. If the backlash is too small, increase the backlash using the following procedure:
9.1. Remove the differential bearing cap bolts and the differential bearing caps.
Mark the differential bearing caps left or right.
9.2. Remove the differential assembly with the differential bearing cups and the shims.
Mark the differential bearing cups and the shims left or right.
9.3. Measure the thickness of left side shim pack.
Measure the production shim or the shim and service spacer in 3 locations.
Measure each shim separately.
9.4. Calculate the average of the 3 measurements for each shim.
Add the average of each of the shim measurements together.
Record the measurement. This is the thickness for the left side shim pack.
9.5. Assemble a new left side shim pack by decreasing the appropriate amount of thickness from the original left side shim pack. If the original shim is cast iron production shim, assemble the shim pack using a service spacer and service shims. For example, to increase the backlash by 0.05 mm (0.002 inch), remove 0.10 mm (0.004 inch) of thickness from the left side shim pack.
9.6. Measure the thickness of right side shim pack. Measure the shim or the shim and service spacer in 3 locations. Measure each shim separately.
9.7. Calculate the average of the 3 measurements for each shim. Add the average of each of the shim measurements together. Record the measurement. This is the thickness for the right side shim pack.
9.8. Assemble a new right side shim pack by increasing the appropriate amount of thickness to the original right side shim pack. If the original shim is cast iron production shim, assemble the shim pack using a service spacer and service shims. For example, to increase the backlash by 0.05 mm (0.002 inch), add 0.10 mm (0.004 inch) of thickness to the right side shim pack.
10. If the backlash is too large, decrease the backlash using the following procedure:
10.1. Remove the differential bearing cap bolts and the differential bearing caps. Mark the differential bearing caps left or right.
10.2. Remove the differential assembly with the differential bearing cups and the shims. Mark the differential bearing cups and the shims left or right.
10.3. Measure the thickness of left side shim pack. Measure the production shim or the shim and service spacer in 3 locations. Measure each shim separately.
10.4. Calculate the average of the 3 measurements for each shim. Add the average of each of the shim measurements together. Record the measurement. This is the thickness for the left side shim pack.
10.5. Assemble a new left side shim pack by increasing the appropriate amount of thickness to the original left side shim pack. If the original shim is cast iron production shim, assemble the shim pack using a service spacer and service shims. For example, to increase the backlash by 0.05 mm (0.002 inch), add 0.10 mm (0.004 inch) of thickness to the left side shim pack.
10.6. Measure the thickness of right side shim pack. Measure the shim or the shim and service spacer in 3 locations. Measure each shim separately.
10.7. Calculate the average of the 3 measurements for each shim. Add the average of each of the shim measurements together. Record the measurement. This is the thickness for the right side shim pack.
10.8. Assemble a new right side shim pack by decreasing the appropriate amount of thickness to the original right side shim pack. If the original shim is cast iron production shim, assemble the shim pack using a service spacer and service shims. For example, to decrease the backlash by 0.05 mm (0.002 inch), remove 0.10 mm (0.004 inch) of thickness to the right side shim pack.
11. Install the differential assembly with the differential bearing cups.
12. Install the left side service spacer between the axle housing and the differential case.
13. Install the right side service spacer between the axle housing and the differential case.





14. Install the left side service shim or shims using the J25588, if necessary.
The service shim or shims must be installed between the service spacer and the differential bearing cup.
15. Install the right side service shim or shims using the J25588, if necessary.
The service shim or shims must be installed between the service spacer and the differential bearing cup.

Notice: Use the correct fastener in the correct location. Replacement fasteners must be the correct part number for that application. Fasteners requiring replacement or fasteners requiring the use of thread locking compound or sealant are identified in the service procedure. Do not use paints, lubricants, or corrosion inhibitors on fasteners or fastener joint surfaces unless specified. These coatings affect fastener torque and joint clamping force and may damage the fastener. Use the correct tightening sequence and specifications when installing fasteners in order to avoid damage to parts and systems.

16. Install the differential bearing caps and bolts.

Tighten the bolts to 75 Nm (55 ft. lbs.).
17. Recheck the backlash and adjust, if necessary.
18. Once backlash is correct, perform a gear tooth contact pattern check in order to ensure proper alignment between the ring and pinion gears.