The gear contact pattern check is not a substitute for adjusting the pinion depth and backlash. Use this method in order to verify the correct running position of the ring gear and the output shaft. Gear sets which are not positioned properly may be noisy and/or have a short life span. A pattern check ensures that when best contact has been obtained between the ring gear and the output shaft, the system will produce low noise and have a long life.
Output Shaft and Ring Gear Identification
Production output shaft and ring gears are manufactured by using a 2-cut or a 5-cut method. The 2-cut output shafts and ring gears can be identified by having a groove cut into the outside edge of the ring gear and a ring on the stem of the output shaft. The gear tooth contact patterns that are produced from each style of gear set differ slightly. A 2-cut gear will produce a pattern that is bias from the toe to the heel of the tooth (drive side), while a 5-cut gear set will produce a square pattern from the toe to the heel of the tooth (drive side). When diagnosing the gear tooth contact pattern, regardless of what type of gear set it is, a correct pattern will be centered within the area of the tooth, from toe to heel and from top to bottom.
Gear Tooth Nomenclature
The side of the ring gear tooth which curves outward, or is convex, is the drive side (4). The concave side is the coast side (3). The end of the tooth nearest the center of the ring gear is the toe end (2). The end of the tooth farthest away from the center is the heel end (1).
Adjustments Affecting Tooth Contact
The following 2 adjustments affect the tooth contact pattern:
| • | Backlash adjustment |
| • | Pinion depth adjustment |
The effects of bearing preloads are not readily apparent on hand-loaded tooth contact pattern tests. However, bearing preloads should be within specifications before proceeding with backlash and pinion depth adjustments.
Backlash Adjustment
The backlash can be adjusted by either varying the thickness of the side bearing shims from side to side. By adjusting the shim thickness, the case and ring gear assembly will move closer to or further away from the pinion. In most cases, adjusting the backlash will correct an abnormal contact pattern. This adjustment will also be used to set the side bearing preload.
| • | If the thickness of the right shim is increased, along with an equal decrease in the thickness of the left shim, the backlash will increase. |
| • | If the thickness of the left shim is increased, along with an equal decrease in the thickness of the right shim, the backlash will decrease. |
Pinion Depth Adjustment
Adjust the position of the pinion by increasing or decreasing the distance between the pinion head and the centerline of the ring gear. Decreasing the distance moves the pinion closer to the centerline of the ring gear. Increasing the distance moves the pinion farther away from the centerline of the ring gear.
Testing Procedure
- Remove the lubricant from the transfer case. Carefully clean each tooth of the ring gear.
- Use a medium stiff brush in order to sparingly apply gear marking compound, GM P/N 1052351 (Canadian P/N 10953497) or equivalent, to all of the ring gear teeth.
- Turn the output shaft so that the ring gear rotates 3 full revolutions.
- Turn the output shaft in the opposite direction so that the ring gear rotates 3 full revolutions in the opposite direction.
- Observe the pattern on the ring gear teeth. Compare the pattern with the following illustrations.
Important: Avoid turning the ring gear excessively.
Correct Contact Pattern
Condition
The backlash and pinion depth is correct.
Correction
None required.
Service Hints
Loose bearings on the output shaft or in the transfer case may cause patterns that vary. If the contact pattern varies, inspect the following preload settings:
| • | Total assembly |
| • | Transfer case |
| • | Pinion |
If these settings are correct, inspect for damage or incorrectly assembled parts.
Drive Side Heel -- Coast Side Toe Contact Pattern
Condition
The backlash is incorrect. The ring gear is too far away from the pinion.
Correction
Decrease the backlash. Move the ring gear closer to the pinion by adjusting the side bearing shim thickness.
Drive Side Toe -- Coast Side Heel Contact Pattern
Condition
The backlash is incorrect. The ring gear is too close to the output shaft.
Correction
Increase the backlash. Move the ring gear away from the pinion by adjusting the side bearing shim thickness.
Drive Side Heel -- Coast Side Heel Contact Pattern
Condition
The backlash is incorrect. The ring gear is too far away from the pinion.
Correction
Decrease the backlash. Move the ring gear closer to the pinion by adjusting the side bearing shim thickness.
Drive Side Toe -- Coast Side Toe Contact Pattern
Condition
The backlash is incorrect. The ring gear is too close to the output shaft.
Correction
Increase the backlash. Move the ring gear away from the pinion by adjusting the side bearing shim thickness.
High Flank Contact Pattern
Condition
The pinion depth is incorrect. The pinion gear is too far away from the ring gear.
Correction
Increase the pinion depth. Move the pinion gear closer to the ring gear by increasing the pinion shim thickness.
Low Flank Contact Pattern
Condition
The pinion depth is incorrect. The pinion gear is too close to the ring gear.
Correction
Decrease the pinion depth. Move the pinion gear away from the ring gear by decreasing the pinion shim thickness.
