304 TROUBLESHOOTING
TROUBLESHOOTING DRIVE
AXLE PROBLEMS
First, determine when the noise is most no-
ticeable.
Drive Noise: Produced under vehicle ac-
celeration.
Coast Noise: Produced while coasting with
a closed throttle.
Float Noise: Occurs while maintaining
constant speed (just enough to keep speed
constant) on a level road.
External Noise Elimination
It is advisable to make a thorough road test to
determine whether the noise originates in
the rear axle or whether it originates from the
tires, engine, transmission, wheel bearings
or road surface. Noise originating from other
places cannot be corrected by servicing the
rear axle.
ROAD NOISE
Brick or rough surfaced concrete roads pro-
duce noises that seem to come from the rear
axle. Road noise is usually identical in Drive
or Coast and driving on a different type of
road will tell whether the road is the prob-
lem.
TIRE NOISE
Tire noise can be mistaken as rear axle
noise, even though the tires on the front are
at fault. Snow tread and mud tread tires or
tires worn unevenly will frequently cause vi-
brations which seem to originate elsewhere;
temporarily, and for test purposes only,
in-
flate the tires to 40-50 Ibs. This will signifi-
cantly alter the noise produced by the tires,
but will not alter noise from the rear axle.
Noises from the rear axle will normally cease
at speeds below 30 mph on coast, while tire
noise will continue at lower tone as speed is
decreased. The rear axle noise will usually
change from drive conditions to coast condi-
tions, while tire noise will not. Do not forget
to lower the tire pressure to normal after the
test is complete.
ENGINE/TRANSMISSION NOISE
Determine at what speed the noise is most
pronounced, then stop in a quiet place. With
the transmission in Neutral, run the engine
through speeds corresponding to road speeds
where the noise was noticed. Noises pro-
duced with the vehicle standing still are com-
ing from the engine or transmission.
FRONT WHEEL BEARINGS
Front wheel bearing noises, sometimes con-
fused with rear axle noises, will not change
when comparing drive and coast conditions.
While holding the speed steady, lightly apply
the footbrake. This will often cause wheel
bearing noise to lessen, as some of the weight
is taken off the bearing. Front wheel bearings
are easily checked by jacking up the wheels
and spinning the wheels. Shaking the wheels
will also determine if the wheel bearings are
excessively loose.
REAR AXLE NOISES
Eliminating other possible sources can nar-
row the cause to the rear axle, which nor-
mally produces noise from worn gears or
bearings. Gear noises tend to peak in a nar-
row speed range, while bearing noises will
usually vary in pitch with engine speeds.
Noise Diagnosis
The Noise Is:
Most Probably Produced By:
1. Identical under Drive or Coast
2. Different depending on road surface
3. Lower as speed is lowered
4. Similar when standing or moving
5. A vibration
6. A knock or click about every two tire revolu
tions
7. Most pronounced on turns
8. A steady low-pitched whirring or scraping,
starting at low speeds
9. A chattering vibration on turns
10. Noticed only in Drive, Coast or Float conditions
Road surface, tires or front wheel bearings
Road surface or tires
Tires
Engine or transmission
Unbalanced tires, rear wheel bearing, unbalanced
driveshaft or worn U-joint
Rear wheel bearing
Damaged differential gears
Damaged or worn pinion bearing
Wrong differential lubricant or worn clutch plates
(limited slip rear axle)
Worn ring gear and/or pinion gear
