Gear Tooth Contact Pattern C H Eck; Test - GMC T Series 1994 Repair Manual

GEAR TOOTH CONTACT
PATTERN CHECK
Before final assembly of the differential, a gear tooth
contact pattern check must be performed.
A gear tooth contact pattern check is NOT a substi­
tute for adjusting pinion depth and backlash as previ­
ously 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, have a short life, or both. The best contact
between the ring gear and the drive pinion for low noise
level and long life can be assured with a pattern check.
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 27).

TEST

1. Wipe oil out of the carrier and carefully clean each
tooth of the ring gear.
2. Apply gear marking compound sparingly to all ring
gear teeth using a medium stiff brush. When prop­
erly used, the area of pinion tooth contact will be
visible when a hand load is applied.
3. Apply a load until a torque of 62 N-m (45 lbs. ft.) is
required to turn the pinion.
A test made 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. Excessive turning of the ring
gear is not recommended.
4. Observe the pattern on the ring gear teeth and
compare with figure 28.
ADJUSTMENTS AFFECTING TOOTH CONTACT
Two adjustments can be made which will affect the
tooth contact pattern. These are backlash and pinion
depth. The effects of bearing preloads are not easily
seen on hand loaded teeth pattern tests. These adjust­
ments should be within specifications before proceeding
with the backlash and the drive pinion adjustments.
It may be necessary to adjust both pinion depth and
backlash to obtain the correct pattern.
The position of the drive pinion 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 differential to compensate for
manufacturing tolerances. Increasing the shim thickness
will move the pinion closer to the center line of the ring
gear.
Backlash is adjusted by the side bearing adjusting
sleeves which move the case and ring gear assembly
closer to, or further 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 back­
lash, turn the right sleeve in and turn the left sleeve out
an identical amount.
Important
The contact pattern should be located in the middle
of the ring gear teeth face (figure 28).
FINAL ASSEMBLY
Remove or Disconnect (Figures 1, 2 and 24)
1. Four case bolts (28) (figure 24).
2. Right carrier case half.
l y i Clean
• Sealing surfaces on the carrier case halves.
Remove all oil and grease. Use a chlorinated sol­
vent, such as carburetor cleaner.
+«-
Install or Connect (Figures 1, 2, 14, and 29)
NOTICE: For steps 3, 4, 7, and 12 refer to
"Notice" on page 4C3-1.