Tooth Contact Pattern Test

^ Tool Required:
- J 42178 Differential Side and Pinion Alignment Kit

Important: It is very important that the tooth contact be tested before the differential is taken apart. Variations in the differential and/or drive pinion gear inner bearing may cause the drive gear to be too close, or too far away, from the ring gear.

1. Remove the rear axle differential from the vehicle.
2. Clean all the dirt from the cover area before removing the cover.
3. Remove the housing cover.
4. Wipe the axle lubricant out of the housing.
5. Carefully clean each tooth of the ring gear.
6. Use a medium stiff brush to apply gear marking compound sparingly to all the ring gear teeth. When properly applied the area of the differential drive pinion gear tooth contact is visible when hand load is applied.
7. Insert the J 42178 to the differential side bearing bore.
8. Use a ratchet to hold the J 42178 stationary.
9. Rotate the pinion gear flange so that the ring gear rotates one full revolution.
10. Reverse the rotation so that the ring gear rotates one revolution in the opposite direction.
11. Observe the pattern on the ring gear teeth and compare to the following:
- Low Flank Contact (evident by contact in the valley between the gear teeth): Decrease the pinion gear bearing shim thickness, this will move the pinion gear out toward the ring gear centerline.
- High Face Contact (evident by contact on the outboard edge of the gear tooth): Increase the pinion gear bearing shim thickness, this will move the pinion gear in toward the ring gear centerline.
- Toe Contact (evident by contact on the lower edge of the gear tooth): Increase the backlash, this will move the area of pinion gear contact with the ring gear toward the heel.
- Heel Contact (evident by contact on the upper edge of the gear tooth): Decrease the backlash, this will move the of pinion gear contact with the ring gear toward the toe.
- Desired Contact Pattern: Pinion gear contact in center of the ring gear tooth.
12. Reinstall the housing cover.
13. Install the rear axle differential to the vehicle.