GMC T Series 1994 Repair Manual page 158

2. Apply gear marking compound (GM P/N 1052351)
or equivalent to all ring gear teeth using a medi-
um-stiff brush. When properly used, the area of
pinion tooth contact will be visible when hand load
is applied.
NOTICE: Refer to "Notice" on page 4B3-1.
3. Tighten the bearing cap bolts to 80 N-m (60 lbs.
ft.).
4. Expand the brake shoes until a torque of 54 to 68
N-m (40 to 50 lbs. ft.) is required to turn the pinion.
A test made without loading the gears will not
give a satisfactory pattern. Turn the pinion flange
with a wrench until the ring gear rotates one full
revolution, then reverse the rotation until the ring
gear rotates one revolution in the opposite direc­
tion.
5. Observe the pattern on the ring gear teeth and
compare with figure 27.
ADJUSTM ENTS AFFECTING
TOOTH CONTACT
Two adjustments can be made that affects tooth con­
tact pattern; backlash and pinion depth. The effects of
bearing preloads are not readily apparent on hand load­
ed tooth contact pattern tests. However, these adjust­
ments should be within specifications before proceeding
with backlash and drive pinion adjustments.
The position of the drive pinion is adjusted by
increasing or decreasing the distance between the pin­
ion head and the centerline of the ring gear. Decreasing
the distance will move the pinion closer to the center-
line of the ring gear. Increasing the distance will move
the pinion farther away from the centerline of the ring
gear.
Backlash is adjusted using side bearing adjusting
shims that move the entire case and ring gear assem­
bly closer to or farther from the drive pinion. The adjust­
ing shims are also used to set side bearing preload.
If the thickness of the right shim is increased (along
with decreasing the left shim thickness), backlash will
increase.
If the thickness of the left shim is increased (along
with decreasing the right shim thickness), backlash will
decrease.