Chevrolet 10 Series 1968, Service Manual

Page: 190 / 713

REAR SUSPENSION AND DRIVE LINE 4-21
MAINTENANCE AND ADJUSTMENTS
LUBRICANT
The lubricant level should be periodically checked and
maintained at level of fille r plug with a warm axle. See
the lubrication section of this manual for lubricant
r e commendations.
Lubricant Leaks
Lubricant leaks should be checked for at the pinion
flange oil seal, sealing area of joint between differential
carrier and axle housing, lubricant fille r plug, housing
bowl cover, and at axle shaft bearings. Correction of
these leaks consists of replacing the defective seals or
gaskets involved as described in this section.
U-BOLTS AND HUB NUTS
Axle housing to rear spring " U " bolts and wheel
hub nuts should be periodically inspected for secure
installation.
REAR AXLE NOISE DIAGNOSIS
Mechanical failures of the rear axle are relatively
simple to locate and correct. Noise in a rear axle is a
little more difficult to diagnose and repair. One of the
most essential parts of rear axle service is proper
diagnosis.
One of the cardinal points of axle noise diagnosis is the
fact that all rear axles are noisy to a certain degree. The
action of transmitting the high engine torque through a
90° turn reducing propeller shaft speed produces noise in
rear axles. This point establishes the need for a line
between normal and abnormal or unacceptable axle
noises.
Slight axle noise heard only at a certain speed or under
remote conditions must be considered normal. Axle
noise tends to "peak" at varying speeds and the noise is
in no way indicative of trouble in the axle.
If noise is present in an objectionable form, loud or at
all speeds, an effort should be made to isolate the noise
as being in one particular unit of the vehicle. Axle noise
is often confused with other noises such as tire noise,
transmission noise, propeller shaft vibration and uni­
versal joint noise. Isolation of the noise as in any one
unit requires skill and experience. An attempt to elim i­
nate a slight noise may baffle even the best of diagnosti­
cians.
Such practices as raising tire pressure to
eliminate tire noise, listening for the noise at varying
speeds and on drive, float and coast, and under proper
highway conditions, turning the steering wheel from left
to right to detect wheel bearing noise, will aid even the
beginner in detecting alleged axle noises. Axle noises
fall into two categories: gear noise and bearing noise.
Gear Noise
Abnormal gear noise can be recognized since it pro­
duces a cycling pitch and will be very pronounced in the
speed range at which it occurs, appearing under either
" d r iv e ," " flo a t" or "c o a s t" conditions. Gear noise tends
to peak in a narrow speed range or ranges, while bearing
noise will tend to remain constant in pitch. Abnormal
gear noise is rare and usually originates from the scor­
ing of the ring gear and pinion teeth as a result of insuf­
ficient or improper lubricant in new assemblies. Side
gears rarely give trouble as they are used only when the
rear wheels travel at different speeds.
Bearing Noise
Defective bearing will always produce a rough whine
that is constant in pitch and usually most noticeable under
" d r iv e " conditions. This fact will allow you to distinguish
between bearing noise and gear noise.
1. Pinion bearing noise resulting from a bearing failure
can be identified by a constant rough sound. Pinion
bearings are rotating at a higher speed than differen­
tial side bearings or axle shaft bearings. This par­
ticular noise can be picked up best by testing the car
on a smooth road (black top). However, care should
be taken not to confuse tire noise with bearing or
gear noise. If any doubt exists, tire treads should be
examined for irregularities that would produce such
noise.
2. Wheel bearing noise may be confused with rear axle
noise. To differentiate between wheel bearings and
rear axle, drive the vehicle on a smooth road at
medium-low speed. With traffic permitting, turn the
vehicle sharply right and left. If noise is caused by
wheel bearings, it will increase in the turns because
of the side loading. If noise cannot be isolated to
front or rear wheel bearings, inspection will be
necessary.
3. Side bearings will produce a constant rough noise of
a slower nature than pinion bearings. Side bearing
noise will not fluctuate in the above wheel bearing
test.
COMPONENT PART REPLACEMENT
2400, 2900, 3300, 3500 AND 3600 LB.
CAPACITY (SALISBURY-TYPE) AXLES
Axle Assembly
Construction of the axle assembly is such that service
operations may be performed with the housing installed in
the vehicle or with the housing installed in a holding fix­
ture. The following removal and installation procedure
is necessary only when the housing requires replacement.
Removal
1. Raise vehicle, place stand jacks under frame side
rails and remove rear wheels.
2. Support rear axle assembly with a hydraulic jack, or
other suitable lifting device, so that tension is re ­
lieved in springs, tie rod, and shock absorbers.
3. On vehicles so equipped, disconnect tie rod at axle
housing bracket or at differential carrier.
4. Remove trunnion bearing " U " bolts from the axle
companion flange, separate trunnion from flange, po­
CHEVROLET TRUCK SERVICE MANUAL