Gear Tooth Contact Pattern Inspection

Before final assembly of the differential, perform a gear tooth pattern check.
This 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 drive pinion. Gear sets which are not positioned properly may be noisy, have a short life, or both. A pattern check ensures the best contact between the ring gear and the drive pinion for low noise and long life.

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).


Testing Procedure
1. Wipe the oil out of the axle housing. Carefully clean each tooth of the ring gear.
2. Use a medium stiff brush in order to sparingly apply gear marking compound to all of the ring gear teeth.

Important: A test made without loading the gears does not give a satisfactory pattern.

3. Use the parking brake in order to apply a load until a torque of 13 Nm (9.6 ft. lbs.) is required in order to turn the pinion.

Important: Avoid excessive turning of the ring gear.

4. Turn the companion flange with a wrench so that the ring gear rotates six full revolutions.
5. Reverse the rotation so that the ring gear rotates six revolutions in the opposite direction.





6. Observe the pattern on the ring gear teeth. Compare the pattern with the following illustrations. Use the legend below:
6.1. (1) Toe
6.2. (2) Heel
6.3. (3) Coast side (Concave)
6.4. (4) Drive side (Convex)

Condition
^ The pinion depth is correct.
^ The backlash is correct.


Condition





^ The pinion depth is correct.
^ The backlash is incorrect- too much clearance between the pinion gear and the ring gear.

Correction
Move the ring gear closer to the pinion gear by reducing backlash.

Condition





^ The pinion depth is correct.
^ The backlash is incorrect- too little clearance between the pinion gear and the ring gear.

Correction
Move the ring gear away from the pinion gear by increasing backlash.

Condition





^ The pinion depth is correct.
^ The backlash is incorrect- too much clearance between the pinion gear and the ring gear.

Correction
Move the ring gear closer to the pinion gear by reducing backlash.


Condition





^ The pinion depth is correct.
^ The backlash is incorrect- too little clearance between the pinion gear and the ring gear.

Correction
Move the ring gear away from the pinion gear by increasing backlash.

Condition





^ The pinion depth is incorrect- high flank contact pattern.
^ The backlash is correct.

Correction
Move the pinion gear closer to the ring gear by increasing pinion shim.

Condition





^ The pinion depth is incorrect- low flank contract pattern.
^ The backlash is correct.

Correction
Move the pinion gear away from the ring gear by decreasing pinion shim.


Service Hints
The shims which adjust the pinion depth are located:
^ Between the inner pinion bearing cone and the rear to the pinion gear.
^ Between the inner pinion bearing cup and the rear axle housing.

Adjustments Affecting Tooth Contact
There are two adjustments that affect the tooth contact pattern: backlash and drive pinion depth. 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 drive pinion adjustments.
Adjust the position of the drive 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.
Adjust the backlash by means of the side bearing adjusting shims which move the case and ring gear assembly closer to, or farther from, the drive pinion. Also use the adjusting shims 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, 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.