GMC 1982 Light Duty Truck Service Manual page 423

For example, hypoid gear tooth scoring as seen in figure
4B-10 generally results from the following: insufficient
lubricant improper breakin, improper lubricant, insufficient
gear backlash, improper ring and pinion gear alignment, or
loss of drive pinion nut torque. The scoring will progressively
lead to complete erosion of the gear tooth, or gear tooth
pitting and eventual fracture if the initial scoring condition
is not corrected. Another cause of hypoid tooth fracture is
extended overloading of the gear set which will produce
fatigue fracture, or shock loading which will result in sudden
failure.
Differential pinion and side gears rarely give trouble.
Common causes of differential failure are shock loading,
extended overloading, and seizure of the differential pinions
to the cross shaft resulting from excessive wheel spin and
consequent lubrication breakdown.
The second type of gear noise pertains to the mesh
pattern of the gear teeth. This form of abnormal gear noise
can be recognized as it produces a cycling pitch (whine) and
will be very pronounced in the speed range at which it
occurs, appearing under either "drive", "float" or "coast"
conditions. "Drive" is acceleration or heavy pull. "C oast"
is with a closed throttle and vehicle in gear and "float" is
using just enough throttle to keep the car from driving the
engine-the vehicle slows down gradually but engine still
pulls slightly. Gear noise tends to peak in a narrow speed
range or ranges, and will tend to remain constant in pitch.
Bearing noise will vary in pitch with vehicle speeds. See
figure 4B-7.
M A IN T E N A N C E A N D LUBRICATIO N
Refer to Section OB for periodic maintenance and
lubrication requirements.
O PERATIO N AL CHECK A N D ADJUSTM ENTS
Four adjustments are essential for proper operation of
the differential and its related parts. These adjustments are
a) Pinion Bearing Preload, b) Side Bearing Preload, c)
Pinion Depth and d) Ring Gear-to-Pinion Backlash.
Pinion Bearing Preload is set to specifications in step 9
o f 'Drive Pinion Reassembly4.
Side Bearing Preload is set to specifications in step 6 of
'Differential Case-Installation and Adjustment1.
Following service to the Differential assembly or to the
Drive Pinion, the Pinion Depth and Ring-Gear-to-Pinion
Backlash be checked, using a Gear Tooth Contact
must
Pattern Check as outlined below.
G e a r Tooth Contact Pattern Check
Prior to final assembly of the differential, a Gear Tooth
Contact Pattern Check is necessary to verify the correct
realtionship between ring gear and drive pinion. G ear sets
which are not positioned properly may be noisy, or have
short life, or both. With a pattern check, the most desireable
contact between ring gear and drive pinion for low noise
level and long life can be assured.
G ear Tooth N o m enclature
The side of the ring gear tooth which curves outward,
or is convex, is referred to as the 'drive4 side. The concave
side is the 'coast' side. The end of the tooth nearest center of
ring gear is referred to as the 'toe-in' end. The end of the
tooth farthest away from center is the 'heeP end. Toe end of
tooth is smaller than heel end. See figure 4B-8.
P a t t e r n C h e c k
1. Wipe oil out of carrier and carefully clean each tooth of
ring gear.
2. Use gear marking compound and apply this mixture to
ring gear teeth. When properly applied, the area of
tooth contact will be clearly visible after load is applied.
3. Tighten bearing cap bolts to specifications.
4. Apply load to gears by expanding brake shoes or by
wrapping a heavy rag around the companion flange to
resist rotation.
A test made without loading the gears will not
NOTICE:
give a satisfactory pattern. Turn companion flange with
wrench so that ring gear rotates one full revolution then
reverse rotation so that ring gear rotates one revolution
in opposite direction. Excessive turning of ring gear is
not recommended.
5. Observe pattern on ring gear teeth and compare with
figure 4B-9. Make adjustments as outlined below.
6. The important thing to achieve in the pattern check and
subsequent adjustments is to locate the contact pattern
centrally on the face of the ring gear teeth.
Pinion D epth A d ju s tm e n t
1. The pinion depth shim may be replaced as necessary to
place the drive pinion at the correct depth. See figure
4B-9.
2. Depth shims are available from .006 inch to .024 inch,
in increments of .001 inch.
Backlash A d ju s tm e n t
1. Remove locking retainers from side bearing adjusting
nuts.
2. Move adjusting nuts
achieve proper backlash.
a. To increase backlash, loosen the left adjusting nut
and tighten the right adjusting nut
b. To decrease backlash, loosen the right adjusting nut
and tighten the left adjusting nut
REAR A X LE
in or out to
an equal amount
an equal amount.
an equal amount.
4 B -9