Gear Tooth Pattern Check; Adjustments Affecting Tooth Contact - GMC T Series 1994 Repair Manual

4. Place the indicator stem at the heel end of a tooth.
• Set the dial indicator so the stem is in line with
the gear rotation and perpendicular to the tooth
angle (figure 25).
NOTICE: Refer to "Notice" on page 4B2-1.
5. Install the differential caps and bolts.
Tighten
&
• The bolts to 80 N-m (60 lbs. ft.).
6. Check and record the backlash at three or four
points around the ring gear.
• The pinion must be held stationary when check­
ing backlash.
• The backlash should be the same at each point
within 0.05 mm (0.002 inch). If the backlash
varies more than 0.05 mm (0.002 inch), check
for burrs, a distorted case flange, uneven bolt­
ing conditions, or foreign matter between the
case and ring gear.
7. Backlash at the minimum lash point measured
should be between 0.13 to 0.23 mm (0.005 to
0.009 inch) for all new gear sets.
8. If the backlash is not within specifications, move
the ring gear in or out from the pinion by increasing
the thickness of one shim, and decreasing the
thickness of the other shim the same amount. This
will maintain the correct axle side bearing preload.
• Moving 0.003 inch worth of shim from one side
of the differential to the other will change the
backlash adjustment by 0.002 inch.
9. Recheck the backlash and correct as necessary.
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 pin­
ion 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 case and carefully clean
each tooth of the ring gear (figure 26).
2. Apply gear marking compound (GM P/N 1052351)
or equivalent sparingly to all ring gear teeth using a
medium-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
lbs. ft. is required to turn the pinion.
Important
• A test made without loading the gears will not
give a satisfactory pattern. Turn the pinion
flange with a wrench so the ring gear rotates
one full revolution, then reverse the rotation so
the ring gear rotates one revolution in the oppo­
site direction.
5. Observe the pattern on the ring gear teeth and
compare this with figure 27.
ADJUSTM ENTS AFFECTING
TOOTH CONTACT
Two adjustments can be made that affect 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.