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5-6
NOISE DIAGNOSIS
REAR
AXLE ASSEMBLY
(176)
rmssion
still in neutral, run engine through
speeds while slowly disengaging and engaging
clutch. If noise disappears with clutch disen-
gaged, it is caused by
transmission.
If
noise"
continues regardless of clutch position, it is
caused by the
engine.
5-4 REAR AXLE N
OISES
If a careful test of the car shows that the
noise is not caused by external items as de-
scribed in paragraph 5-3 above, it is then
reasonable to assume that the noise is caused
by the rear axle assembly.
a. Testing Rear Axle
The
rear axle should be tested on smooth
road to avoid road noise. It is never advisable
to test rear axle for noise by running engine
with transmission in high gear with rear
wheels jacked up. Without normal loading to
take up allowable clearances of parts and the
cushioning afforded by the tires, the rear axle
will be quite noisy when operated by power
while resting on car stands.
b. Rear Wheel Bearing Noise
Noises in the rear axle assembly may be
caused
by faulty rear wheel bearings, faulty
differential or pinion shaft bearings, differen-
tial side gears and pinions
worn,
or by a mis-
matched, improperly adjusted or scored ring
and pinion gear set.
A rough rear wheel bearing produces a vibra-
tion or growl which continues with car coast-
ing with transmission in neutral. A brinnelled
rear wheel bearing causes a knock or click
approximately
every two revolutions of rear
wheel since the bearing rollers do not travel
at the same speed as the rear axle and wheel.
c. Pinion
Bearing
Noise
Rough
or brinnelled pinion bearings
p
r oduce
a continuous whine starting at a
relatively
low
speed. The noise is most pronounced
on lig ht
load drive between 18 and 25 miles per hour.
d.
Different ia l Side
Gea r and Pinion Noise
Differential side gears and
pinions seldom
cause noise since their movement is relatively
slight
on straight ahead driving. Noise pro-
duced by these gears will be most
pronounced
on turns.
e.
Ring a
nd
Pinion
Gear
Noise
Noise produced by the ring and pinion gear
set generally shows up as drive noise, coast
noise, or float noise.
1.
Drive
noise
is most pronounced on con-
stant acceleration through the speed range of
15 to 45 miles per hour.
2. Coast nois
e
is most pronounced when car is
allowed to coast through the speed range from
45 to 15 miles per hour, with clutch engaged
and throttle closed.
3. Float noise
is most pronounced while hold-
ing the car speed constant at intervals between
15 and 45 miles
per
hour.
4.
Drive,
coast, and float noises
will be very
rough and irregular if the differential or pinion
shaft bearings are
rough,
worn, or loose.
5
-5 CHECKS
FOR
CAUSE OF REAR
AXLE N
OISE
If there is any doubt about the cause of
noise in the rear axle assembly, the following
progressive checking procedure will assist in
determining the cause. The paragraph num-
bers given in the checks
refer
to paragraph in
which repair procedure is given.
1. Place car stands solidly under rear axle
housing so that wheels are clear of floor.
2. Spin rear wheels by
hand
while listening
at hubs for evidence of rough or brinnelled
wheel bearing. Care must be used to avoid mis-
taking differential gear noise for bearing
noise.
If in doubt, remove rear axle shafts and bear-
ings for examination (par. 5-8, 5-9, 5-12)
.
3. If rear wheel bearings are not noisy, or
t
hey
are not responsible for all rear axle noise,
drain rear axle housing by removing lower
cover bolts, then reinstall bolts. Thoroughly
flush rear axle housing with SAE 10-W or
flushing oil. When flushing, put transmission
in
h
igh gear and run rear axle slowly for one
or two
minutes.
CAUTION:
Do not suddenly
accelerate or "gun" the engine and do not ex-
ceed a speed of
25
MPH. Do not use
gasoline,
kerosene, or steam for flushing (see
par.
5-12).
Drain
h
ousing , remove cover
and
wipe out
housing wi
th
clea n cloths.
4.
Check
matching
n
umber s on ring and pin-
ion gears to make sure that they are
matched
set
(par.
5-19).
5. Examine
ge
ar
teeth for chips or scores
and for proper gear tooth contact (par. 5-6 &
fig
.
5-2).
Check
ring gear lash with dial in-
dicator (par. 5-23).
6. Check differential side bearings for proper
pr eloa d as follows. Loosen all bearing cap bolts
one f
ull turn, tighten
to 20 ft.
lbs.
torque, then
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