GMC 4000 Series Service Manual page 455

Sec. 7B
Page 444
TRANSMISSION ON-VEHICLE SERVICE
squeezed out of position, pieces still under bear­
ing caps, clutch housing, power take-off, and
covers, etc.
10. Cracks or holes in castings.
11. Drain plug loose.
BEARING FAILURES
More than 90% of all bearing failures are
caused by dirt which is always abrasive.
Dirt may enter the bearings during assembly
of the units or be carried into the bearing by the
lubricant while in service. Dirt may enter through
seals, breather or even dirty containers used for
addition or change of lubricant.
Softer material such as dirt, dust, etc.,
usually form abrasive paste or lapping compounds
within the bearings them selves since the unit
pressure between the balls and raceways makes
a perfect pulverizer. The rolling motion tends
to entrap and hold the abrasives. As the balls and
raceways wear, the bearings become noisy. The
lapping acti'on tends to increase rapidly as the
fine steel from the balls and rollway adds to the
lapping material.
Hard coarse material such as chips, etc.,
may enter the bearings during assembly from
hammers, drifts, power chisels,
manufactured within the unit during service from
raking teeth, etc. These chips produce small
indentation in balls and races. Jamming of these
hard particles between balls and races may cause
the inner race to turn on shaft, or the outer race
to turn in the housing.
Corrosion
Water, acid, and corrosive materials formed
by deterioration of l u b r i c a n t
reddish-brown coating and small etched holes
over outer and exposed surfaces of race. Cor­
rosive oxides also act as lapping agent.
Fatigue
All bearings are
must be replaced eventually. Your own operating
experience will dictate mileage replacement of
bearings showing only normal wear.
Shaft Fits
E xcessive looseness under load is very ob­
jectionable because it produces a creeping or
slipping of the inner ring on the rotating shaft.
This causes the surface metal of shaft to scrub
or wear off.
Bearing fits on rotating shafts are usually
specified as tight. When play or looseness, even
.001", exists between the bearing and shaft, there
is a very powerful force tending to rotate the
inner race on the shaft; this force is caused by
the looseness or lost motion between the parts
and disappears when no looseness exists.
G M C S E R V I C E M A N U A L
etc., or be
will produce
subject to fatigue and
BEARING REPLACEMENT
It is far more difficult to remove bearings
from a shaft than to put them on. In most cases
it is necessary to remove the bearing by pulling
on the outer race which can damage the balls
or races. Since such damage is seldom visible,
it does not become known until after complete
reassembly. If a bearing is not going to be re­
placed, avoid removal during low mileage rebuild.
Brinelling caused by improper assembly or
removal - - usually hammering with off-center
blows. Use drivers, preferably under an arbor,
or pullers.
TRANSMISSION REPLACEMENT
The procedures required
transm ission from trucks covered in this manual
are dependent generally upon the type of cabs
(i.e., conventional or tilt), type of body, and
liftin g equipm ent a v ailab le in the rep a ir shop.
Operations other than those included in this sec­
tion may be necessary if the vehicle has special
equipment such as a power take-off unit and
controls, etc.
The required operations will be obvious
upon visual inspection of the vehicle. The instruc­
tions contained herein under "Removal"
"Installation" will serve as a guide in accom­
plishing transmission replacement.
REMOVAL
1. On tilt cab models, disconnect shift con­
trol rods from shift levers on the transmission
remote control assembly.
2. On conventional cab and school bus models
perform the following:
remove the transmission floor pan cover, place
the transmission gearshift lever in "NEUTRAL,"
and then remove the gearshift lever.
NOTE: Remove the gearshift lever using
tool (J-8109) as shown in figure 1. P ress down
and rotate counterclockwise to release gearshift
lever.
3. Place clean lint-free cloth or other suit­
able covering over opening at top of transmission
to prevent entry of dirt or other foreign material.
4. Drain lubricant from transmission.
5. Disconnect speedometer cable from trans­
m ission adapter.
6. Disconnect clutch control linkage.
7. Disconnect parking brake lever and con­
trols (if used).
8. Disconnect propeller shaft from trans­
m ission as described in "PROPELLER SHAFTS"
(SEC. 4D) of this manual.
9. Remove engine ground strap and battery
cable support clip if attached to transm ission or
clutch housing.
to remove the
and
Remove the floor mat,