Ring Gear and Pinion Tooth Pattern Interpretation

Gear Tooth Contact Pattern Check

1. To check the gear tooth contact, paint the gear teeth with the special marking compound. A mixture that is too wet will run and smear; too dry a mixture cannot be pressed out from between the teeth.

2. Rotate the ring gear (use a box wrench on the ring gear attaching bolts as a lever) several complete revolutions in both directions or until a clear tooth contact pattern is obtained.

3. Certain types of gear tooth contact patterns on the ring gear indicate incorrect adjustment. Incorrect adjustment can be corrected by readjusting the ring gear and/or the pinion.

4. The illustration shows acceptable tooth patterns for all axles. In general, desirable tooth patterns should have the following characteristics:

   1. The drive pattern should be fairly well centered on the tooth.
   2. The coast pattern should be fairly well centered on the tooth.
   3. Some clearance between the pattern and the top of the tooth is desirable.
   4. There should be no hard lines where the pressure is high.
      
      Ring Gear Pattern Interpretation
      
      
      
      
      
      

      Item	Part Number	Description
      A	—	Normal or Desirable Pattern (Part of 4209)
      B	—	Backlash Correct. Thinner Pinion Position Shim Required (Part of 4209)
      C	—	Backlash Correct. Thicker Pinion Position Shim Required (Part of 4209)
      D	—	Pinion Position Shim Correct. Decrease Backlash (Part of 4209)
      E	—	Pinion Position Shim Correct. Increase Backlash (Part of 4209)

Pattern Movements Summarized

1. Decreasing backlash moves the ring gear closer to the pinion.

   Drive pattern (convex side of gear) moves slightly lower and toward the toe.

   Coast pattern (concave side of gear) moves lower and toward the toe.

2. Increasing backlash moves the ring gear away from the pinion.

   Drive pattern moves slightly higher and toward the heel.

   Coast pattern moves higher and toward the heel.

3. Thicker pinion position shim with the backlash constant moves the pinion closer to the ring gear.

   Drive pattern moves deeper on the tooth (flank contact) and slightly toward the toe.

   Coast pattern moves deeper on the tooth and toward the heel.

4. Thinner pinion position shim with the backlash constant moves the pinion farther from the ring gear.

   Drive pattern moves toward the top of the tooth (face contact) and toward the heel.

   Coast pattern moves toward the top of the tooth and slightly toward the toe.

An individual gear set need not conform exactly to the ideal pattern to be acceptable. Any combination of drive and coast patterns shown is acceptable.

Since each gear set rolls a characteristic pattern, the patterns shown are considered acceptable and should be used as a guide. The drive pattern is rolled on the convex side of the tooth, and the coast pattern is rolled on the concave side.

NOTE: When making pinion position changes, shims should be changed in the range of 0.05mm (0.002 inch) to 0.10mm (0.004 inch) until correct pattern has been obtained.

The movement of tooth contact patterns with changes in shimming can be summarized as follows:

• Thinner shim, with the backlash set to specifications, moves the pinion farther from the ring gear.
• Thicker shim, with the backlash set to specification, moves the pinion closer to the ring gear.

If the pinion positioning shims are correct:

• Decreasing backlash moves the ring gear closer to the pinion. Drive pattern (convex side of gear) moves slightly lower and toward the toe. Coast pattern (concave side of gear) moves lower and toward the toe.
• Increasing backlash moves the ring gear away from the pinion. Drive pattern moves slightly higher and toward the heel. Coast pattern moves higher and toward the heel.

If the patterns are not correct, make the changes as indicated. The differential case and drive pinion will have to be removed from the carrier housing to change a shim.

Check ring gear backlash by installing a dial indicator on the carrier housing. Check ring gear and pinion backlash at three equally spaced points on the ring gear. Backlash tolerance is 0.23mm (0.005-0.008 inch) and cannot vary more than 0.05mm (0.002 inch) between the three points. If backlash is high, the ring gear must be moved closer to the pinion, by moving shims to the ring gear side to the opposite side. If backlash is low, the ring gear must be moved away from the pinion by moving shims from the ring gear side to the opposite side.