Pontiac Fiero 1988 Service Manual page 868

MUNCIE 282 (5-SPEED) MANUAL TRANSAXLE 7B3-7
Bearing Noise
Differential
side b e a r i n g
noise can easily be
confused with wheel bearing noise. Since side bearings
are preloaded, the noise should not diminish much
when the differential (transaxle is run with the wheels
off the ground.
W h e e l b e a r i n g s
produce a rough growl or
grating sound. This sound will continue when the
vehicle is coasting and the transaxle is in Neutral. Since
these bearings are not preloaded, the noise should
diminish considerably when the wheels are off the
ground.
Brinelling
A brinelled bearing causes a "knock" or "click"
approximately every two revolutions of the wheel
because the bearing rollers do not travel at the same
speed as the wheel.
Brinelling is caused by excessive thrust which
pushes the balls up on the pathway and creates a
triangular shaped dent or "Brinell" spot. Brinnelling
can also be caused by pressing the ring on a shaft or in
a housing through the other ring.
False brinnell occurs as a result of vibration
outside of the area where the bearing is mounted. The
condition is identified by slight brinell marks giving a
washboard effect in the ring. In operation, the effect is
characterized by excessively noisy operation on a low
note.
Lapping
Lapping is caused by fine particles of abrasive
material such as scale, sand or emery which are
circulated by oil and which cause wearing away of
roller and race surfaces. Bearings which are worn
loose, but remain smooth without spalling or pitting,
are the result of dirty oil.
Locking
Locking of bearings is caused by large particles of
foreign material becoming wedged between rollers and
race, usually causing one of the races to turn.
Pre-loading of regular type taper roller bearings, higher
than specified, can also cause locking of bearings.
Pitting
Pitting is a result of normal wear. This shows
itself in the form of pitting on the rolling surface.
Pitting may also result from some installation or
operational conditions, such as indenting from foreign
material.
Spalling
Spalling is caused by overload or incorrect
assembly. Spalled bearings have either flaked or pitted
rollers or races. Incorrect assembly consists of
misalignment, cocking of bearings, or adjustments that
are too tight.
DIAGNOSIS CHAR"
CONDITION PROBABLE CAUSE
A knock at low speeds. a. Worn drive axle CV or TRI-Pot joints.
b. Worn side gear hub counterbore.
Noise most pronounced on turns. Differential gear noise.
Clunk on acceleration or deceleration.
a. Loose engine mounts.
b. Worn drive axle inboard TRI-POT joints.
c. Worn differential pinion shaft in case.
d. Side gear hub counterbore in case
worn oversize.
Clicking noise in turns. Worn outboard CV joint.
Vibration
a. Rough wheel bearing.
b. Bent drive axle shaft.
c. Out of round tires.
d. Tire unbalance.
e. Worn CV joint in drive axle shaft.
f. Incorrect drive axle angle. (Trim Height)
Noisy in Neutral with Engine Running a. Worn input gear bearings.
b. Worn clutch release bearing.
Noisy in First Only
a. Chipped, scored, or worn first-speed
constant-mesh gears.
b. Worn 1-2 synchronizer.