Final Assembly - GMC 1990 Light Truck Repair Manual

4C1-12 / -INCH RING GEAR
8 1 2
TOE CONTACT
INCREASE BACKLASH
HIGH FACE CONTACT
INCREASE PINION SHIM
4. Apply a load until a torque of 54-70 N-m (40-50 ft.
lbs.) is required to turn the pinion.
A test made without loading the gears will not give
a satisfactory pattern. Turn the companion flange
with a wrench so that the ring gear rotates one full
revolution then reverse the rotation so that the ring
gear rotates one revolution in the opposite direction.
E xcessive tu rn in g of the ring gear is not
recommended.
5. Observe the pattern on the ring gear teeth and
compare with figure 26.
ADJUSTMENTS AFFECTING TOOTH CONTACT
Two adjustments can be made which will affect the
tooth contact pattern. These are backlash and the
position of the drive pinion (pinion depth) in the carrier.
The effects of bearing preloads are not easily seen on
hand loaded teeth pattern tests: however, these
adjustments should be within specifications before
proceeding with the backlash and the drive pinion
adjustments.
It may be necessary to adjust both pinion depth and the
backlash to obtain the correct pattern.
The position of the drive pinion is adjusted by
increasing or decreasing the shim thickness between the
pinion head and the inner race of the rear bearing. The
shim is used in the differential to compensate for
manufacturing tolerances. Increasing the shim thickness
will move the pinion closer to the centerline of the ring
gear. Decreasing the shim thickness will move the pinion
farther away from the centerline of the ring gear.
Figure 26—Gear Tooth Contact Pattern
Backlash is adjusted by means of the side bearing
adjusting shims which moves the entire case and ring
gear assembly closer to, or farther from the drive pinion.
(The adjusting shims are also used to set side bearing
preload). To incraese backlash, increase the right shim
and decrease the left shim an equal amount. To decrease
backlash decrease the right shim and increase the left
shim an equal amount.
It is important that the contact pattern be centrally
located up and down on the face of the ring gear teeth.
1. Drive axles. Refer to the proper Light Duty Truck
2. New cover gasket and the cover (12).
LOW FLANK CONTACT
DECREASE PINION SHIM
HEEL CONTACT
DECREASE BACKLASH

FINAL ASSEMBLY

Install or Connect (Figure 1)
Service Manual.
Tighten
£
Cover bolts (14) to 27 N-m (20 ft. lbs.).
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