GMC 1989 Light Duty Truck Repair Manual page 159

4. Expand the brake shoes until a torque of 40 to 50 ft.
lbs. 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
w rench so th at the ring gear rotates one full
revolution, then reverse the rotation so that the ring
gear rotates one revolution in the opposite direction.
5. Observe the pattern on the ring gear teeth and
compare this with figure 26.
T O E C O N T A C T
IN C R E A S E B A C K L A S H
H IG H F A C E C O N T A C T
IN C R E A S E P IN IO N S H IM
8 1
ADJUSTMENTS AFFECTING
Two adjustments can be made which will affect tooth
contact pattern: backlash, and the position of the drive
pinion in the carrier. The effects of bearing preloads are
not readily apparent on hand loaded tooth contact pattern
tests; however, these a djustm ents should be w ithin
specifications before proceeding with backlash and drive
pinion adjustments.
The p o s itio n of the d riv e p in ion is a d ju s te d by
increasing or decreasing the distance between the pinion
head and the centerline of the ring gear. Decreasing the
distance will move the pinion closer to the centerline of
the ring gear. Increasing the distance will move the pinion
farther away from the centerline of the ring gear.
Backlash is adjusted by means of the side bearing
adjusting shims which move the entire case and ring gear
assembly closer to, or farther from, the drive pinion. (The
a d ju stin g shim s 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.
The backlash will decrease if the left shim thickness is
increased (along with a decrease in right shim thickness).
Figure 2 6 — G ear Too th P attern
2
/ -INCH RING GEAR 4B 2 -11
TOOTH CONTACT
L O W F L A N K C O N T A C T
D E C R E A S E P IN IO N S H IM
H E E L C O N T A C T
D E C R E A S E B A C K L A S H
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