Buick LeSabre 1965 Service Manual page 371

REAR AXLE
6-5
b. Rear Axle Noises
If a careful test of car shows that
noise is not caused by external
items as described in subpara-
graph a, it is then resonable to
assume that noise is caused by
rear axle assembly. The rear
axle should be tested on a smooth
level road to avoid road noise. It
is not advisable to test rear axle
for noise by running with rear
wheels jacked up.
Noises in rear axle assembly may
be caused by a faulty propeller
shaft, faulty rear wheel bearings,
faulty differential or pinion shaft
bearings, misalignment between
two U-joints, or worn differential
side gears and pinions; noises
may also be caused by mis-
matched, improperly adjusted, or
scored ring and pinion gear set.
(1) Rear Wheel Bearing Noise.
A rough rear wheel bearing pro-
duces a vibration or growl which
continues with car coasting and
transmission in neutral. A bri-
nelled 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. With
rear wheels jacked up, spin rear
wheels by hand while listening
at hubs for evidence of rough or
brinelled wheel bearing.
(2) Differential Side Gear and
Pinion Noise. Differential side
gears and pinions seldom cause
noise since their movement is
relatively slight on straight ahead
driving. Noise produced by these
gears will be most pronounced
on turns.
(3) Pinion Bearing Noise. Rough
or brinelled pinion bearings pro-
duce a continuous low pitch whir-
ring or scraping noise starting at
relatively low speed.
(4) Ring and Pinion Gear Noise.
Noise produced by the ring and
pinion gear set generally shows
up as drive noise, coast noise,
or float noise.
(a) Drive noise is noise produced
during vehicle acceleration.
(b) Coast noise is noise produced
while allowing car to coast with
throttle closed.
(c) Float noise is noise occur-
ring while just maintaining con-
stant car speed at light throttle
on a level road.
(d) Drive, coast, and float noises
will vary in tone with speed, and
will be very rough and irregular
if the differential or pinion shaft
bearings are rough, worn, or
loose.
c. Body Boom Noise
or Vibration
Objectional "body boom" noise
or vibration at 55-65 MPH can be
caused by an unbalanced propeller
shaft. Excessive looseness at the
s p l i n e can contribute to this
unbalance.
Other items that may also con-
tribute to the noise problem are
as follows:
1. Undercoating or mud on the
shaft causing unbalance.
2. Shaft balance weights missing.
3. Shaft damage such as bending,
dents or nicks.
4. Tire-type roughness. Switch
tires from a known good car to
determine tire fault.
d. Check for Propeller
Shaft Vibration
Objectionable vibrations at high
speed (65 MPH or higher) may be
caused by a propeller shaft that
is out of balance. Out of balance
may be due to a bent shaft.
To determine whether propeller
shaft is causing vibration, drive
car through speed range and note
speed at which vibration is most
pronounced. Shift transmission
into lower gear range, and drive
car at same engine speed as when
vibration was most pronounced
in direct drive. Note effect on
vibration.
To determine engine speed, di-
vide vehicle speed by the follow-
ing transmission gear ratios as
listed below:
1.55 (three speed synchromesh
in second gear)
1.51 (four speed synchromesh in
third gear)
1.76 (automatic transmission in
low range).
EXAMPLE: If vibration is most
pronounced in direct drive at 65
MPH, the same engine speed
would be produced in second gear
(three speed synchromesh) at
65/1.55 = 42 MPH; in third gear
(four speed synchromesh) at
65/1.51 = 43 MPH; in low range
(automatic) at 65/1.76 = 37 MPH.
If the vibration is still present at
the same engine speed whether
in direct drive or in the lower
gear, since the propeller shaft
speed varies, this cannot be the
fault. If the vibration decreases
or is eliminated in the lower
gear, then the propeller shaft is
out of balance and should be re-
balanced. See paragraph 6-17.
See paragraph 6-11 for a more
complete trouble diagnosis.
e. Oil Leaks
It is difficult to determine the
source of some oil leaks. When
there is evidence of an oil leak,
determine source as follows:
(1) Oil coming from the drain
hole under the axle housing at
the brake backing plate is caused
by a leaking axle shaft seal or a
leaking wheel b e a r i n g inner
gasket.
(2) Oil coming from between the
rear pinion flange slinger and the
carrier is caused by a leaking
pinion seal.
Even after the point of leakage
has been determined, it is hard
to tell whether the oil is leaking