GMC 4000 Series Service Manual page 156

DESCRIPTION
Rear hubs on all series trucks are mounted to
axle housing tube on opposed tapered roller bear­
ings as shown in figure 2. Hubs, bearings, and oil
seals are identified with the type of rear axle.
Refer to "Service Parts Identification Decal" to
determine type of axle used on a specific vehicle.
Mounting parts (mainly bearings, seals, and
sleeves) are of primary importance. Brake drum
mounting bolts, studs, and nuts differ in type and
their method of installation on the various series
vehicles will vary.
BEARING MAINTENANCE
All wheel bearings are adjustable for wear.
Satisfactory operation and long life of bearings
depend upon proper adjustment and correct lubri­
cation. If bearings are adjusted too tight, they will
overheat and wear rapidly. Loose adjustment will
cause pounding and will also contribute to steering
difficulties, uneven tire wear, and inefficient brakes.
Bearing adjustment should be checked at regular
inspection periods.
Hubs and bearings should be cleaned, inspect­
ed, and lubricated whenever hubs are removed, or
at intervals indicated in LUBRICATION (SEC. 0)
of this manual.
New hub oil seals should be installed when
servicing bearings if there is the slightest indi­
cation of wear or damage. An imperfect seal may
permit bearing lubricant to reach brake linings,
resulting in faulty brake operation and necessitat­
ing premature replacement of linings.
BEARING ADJUSTMENT
BEARING ADJUSTMENT CHECK
Before checking wheel bearing adjustment,
make sure brakes are fully released and do not
drag. Jack up axle until tires clear the floor. Re­
move axle shafts as directed in "REAR AXLES"
(SEC. 4A) of this manual.
Check bearing play by grasping tire at top and
pulling back and forth, or by using a pry bar under
tire. If bearings are properly adjusted, movement
of brake drum in relation to backing plate or brake
spider will be barely noticeable and wheel will
turn freely. If movement is excessive, adjust as
follows:
G M C S E R V I C E M A N U A L
SECTION 4C
fleoA a n d feea'dnaA.
ADJUSTMENT
1. Jack up axle and remove axle shaft as
directed in "REAR AXLES" (SEC. 4A) of this manual.
2. Remove bearing lock nut and nut lock.
3. With a wrench, tighten adjusting nut to
torque listed in "Specifications," while the wheel
is being rotated in both directions to correctly
position the bearings.
4. Back off the adjusting nut 1/8 to 1/4 turn.
5. Install bearing adjusting nut lock, referring
to figure 1.
a. If vehicle is equipped with type shown in
View A, figure 1, align nearest slot in adjusting
nut with short tang on nut lock and bend tang into
slot on nut. Install lock nut with slots outward and
tighten to torque listed in "Specifications." Then
bend tangs of nut lock into slots in lock nut and
adjusting nut.
b. If vehicle is equipped with type shown in
View B, figure 1, align flat on adjusting nut with
nearest lip of nut lock. Make sure wheel turns
freely; then install nut lock and lock nut. Tighten
lock nut to torque listed in "Specifications." Bend
one lip of nut lock over one flat on each nut.
6. After completing bearing adjustment, re­
check adjustment to make sure wheel turns freely.
Final bearing adjustment should be within 0.001"
to 0.007" end play.
A D JU STIN G
LOCKNUT
NUT
NUT
LOCK
NUT
AD JU STIN G
LOCK
Figure 1 — Rear W h ee l Bearin g A d ju stin g Nuts
Sec. 4C
Page 149
BEARING
W ASH ER
BEARING
NUT
T - 8 9 6