GMC 1989 Light Duty Truck, Repair Manual, Page: 283 / 998

T TRUCK FRONT AXLE 4C3-13
GEAR TOOTH CONTACT
PATTERN CHECK
Before final assembly of the differential, a gear tooth
contact pattern check should be performed.
It should be noted that a gear tooth contact pattern
check is NOT a substitute for adjusting pinion depth and
backlash as previously outlined. It is a method to verify
the correct running position of the ring gear and the drive
pinion. Gear sets which are not positioned properly may
be noisy, or have a short life, or both. With a pattern
check, the best contact between the ring gear and the
drive pinion for low noise level and long life can be
assured.
GEAR TOOTH NOMENCLATURE
The side of the ring gear tooth which curves outward, or
is convex, is referred to as the “ drive” side. The concave
side is the “ coast” side. The end of the tooth nearest the
center of ring gear is referred to as the “ toe” end. The
end of the tooth farthest away from the center is the
“ heel” end. The toe end of the tooth is smaller than the
heel end, (figure 29).
TEST
1. Wipe oil out of carrier and carefully clean each tooth
of the ring gear.
2. Use gear marking compound and apply this mixture
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. Apply a load until a torque of 54-70 N-m (40-50 ft.
lbs.) is required to turn the pinion.
A test make without loading the gears will not give a
satisfactory pattern. Turn the companion flange with
a wrench so that the ring gear rotates one full
revolution then reverse the rotation so that the ring
gear rotates one revolution in the opposite direction.
E x c e s s iv e tu r n in g of th e rin g g e a r is not
recommended.
4. Observe the pattern on the ring gear teeth and
compare with figure 30.
ADJUSTMENTS AFFECTING TOOTH CONTACT
Two adjustments can be made which will affect the
tooth contact pattern. These are backlash and the
position of the drive pinion (pinion depth) in the carrier.
The effects of bearing preloads are not easily seen on
hand loaded teeth pattern tests. These adjustm ents
should be within specifications before proceeding with the
backlash and the drive pinion adjustments.
It may be necessary to adjust both pinion depth and the
backlash to obtain the correct pattern.
The p osition of the d rive p in ion is adjusted by
increasing or decreasing the shim thickness between the
pinion head and the inner race of the rear bearing. The
shim is used in the d iffe re n tia l to c o m p en sate for
m anufacturing tolerences. Increasing the shim thickness
will move the pinion closer to the center line of the ring
gear.
Backlash is adjusted by means of the side bearing
adjusting sleeves which move the entire case and ring
gear assembly closer to, or farther from the drive pinion.
(The adjusting sleeves are also used to set side bearing
preload.) To increase backlash, turn the left sleeve in and
turn the right sleeve out an identical amount. To decrease
backlash, turn the right sleeve in and turn the left sleeve
out an identical amount.
It is important that the contact pattern be centrally
located up and down on the face of the ring gear teeth.
FINAL ASSEMBLY
R em ove or D isco n n ect (Figures 1, 2 and 25)
1. Four case bolts (figure 25).
2. Right carrier case half.
a y
- ► +
Clean
Sealing surfaces on the ca rrie r case halves.
Remove all oil and grease. Use a ch lo rin ated
solvent, such as carburetor cleaner.
Install or C o nn ect (Figure 1, 2 and 31 throu g h
34)
Tools Required:
J 33844 Bearing Installer
J 33893 Axle Seal Installer
J 33799 Shift Housing Seal Installer
J 33842 Differential Pilot Bearing Installer
J 33791 Case Bushing Installer
• Apply a bead of sealer (GM part num ber 1052357
[Loctite 514] or equivalent) to one carrier case
surface.
1. Right carrier case (29).
2. Bolts (28).
&
T ig h ten
• Bolts to 47 N-m (35 ft. lbs.).
• Make sure the sleeves (32) are in the proper
position, as marked previously.
3. Bolts (18) and locks (19).