GMC 1989 Light Duty Truck Repair Manual page 172

4B3-10 91 / 2-INCH RING GEAR
A.
B.
C.
C oncave S ide (Coast)
D.
C onvex S ide (Drive)
Figure 23— Gear T oo th N om enclature
GEAR TOOTH
PATTERN CHECK
Checking the ring gear to pinion tooth pattern is to be
done only after setting up the axle according to the
methods in this section. The pattern check is NEVER to
be used as an initial check, or instead of checking pinion
depth and backlash adjustments. This check is only to be
used to verify the correct adjustment of the gear set after
setup.
1. Wipe all oil out of the carrier, and carefully clean
each tooth of the ring gear (figure 23).
2. Use gear marking compound 1052351 or equivalent
and apply this mixture sparingly to all ring gear
teeth, using a m edium-stiff brush. When properly
used, the area of pinion tooth contact will be visible
when hand load is applied.
3. Tighten the bearing cap bolts to the specified
torque.
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 24.
ADJUSTMENTS AFFECTING
TOOTH CONTACT
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 adjustm ents should be w ithin
specifications before proceeding with backlash and drive
pinion adjustments.
T he p osition of the d rive p in io n is a djusted 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 djustin 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).
F-02017