1988 PONTIAC FIERO Service Repair Manual

481-4 REAR AXLE
Gear Noise
Gear noise (whine) is audible from 20 to 55 mph
under four driving conditions:
1. Light Acceleration - Accelerate slowly.
2. Road Load
- Car
driving load or constant speed.
3. Float - Using enough throttle to keep the car from
driving the engine
- car slows down gradually but
engine still pulls slightly.
4. Coast - Throttle closed and car in gear.
Bearing Noise
Bad bearings generally produce more of a rough
growl or grating sound, rather than the whine typical
of gear noise. Bearing noise frequently "wow-wows" at
bearing rpm, indicating a defective pinion or rear axle
case side bearing. This noise could easily be confused
with rear wheel bearing noise. Inspect and replace as
required.
Rear Wheel Bearing Noise
A rough rear wheel bearing produces a noise
which continues with car coasting at low speed and
transmission in neutral. Noise may diminish some by
gentle braking. With rear wheels jacked up, spin rear
wheels by hand while listening at hubs for evidence of
rough (noisy) wheel bearing.
Knock At Low Speeds
Low speed knock can be caused by worn
universal joints or a side gear hub counterbore in a case
that has worn oversize. Inspect and replace universal
joint or case and side gear as required.
Backlash Clunk
Excessive clunk with acceleration and deceleration
is caused by worn differential pinion gear shaft, excessive
clearance between axle shaft and side gear splines, exces-
sive clearance between side gear hub and counterbore in
case, worn pinion and side gear teeth, worn thrust washers
and excessive drive pinion and ring gear backlash. Re-
move worn parts and replace as required, selecting close
fitting parts when possible. Adjust pinion and ring gear
backlash.
DIAGNOSIS
1. Noise
is the same in "Light Acceleration" or
"Coast".
a. Road noise.
b. Tire noise.
c. Front wheel bearing noise.
d. Rear axle bearing noise.
2. Noise changes on a different type of road.
a. Road noise.
b. Tire noise.
3. Noise tone lowers as car speed is lowered.
a. Tire noise.
b. Front
wheel bearings and rear axle bearings.
c. Gear noise.
4. Similar noise is produced with car standing and
driving. a.
Engine noise.
b. Transmission noise.
c. Exhaust noise.
5. Vibration.
a. Rough rear axle bearing.
b. Unbalanced or damaged propeller shaft.
c. Tire unbalance.
d. Worn universal joint in propeller shaft.
e. Mis-indexed propeller shaft at pinion
flange.
f. Pinion flange runout too great.
6. A knock or click approximately every two
revolutions of the rear wheel.
a. A rear axle bearing.
b. Worn case.
7. Noise most pronounced on turns.
a. Rear axle side gear and pinion noise,
differential gear noise.
b. Axle bearings.
8. A continuous low pitch whirring or scraping
noise starting at relatively low speed.
a. All bearing noise.
9. Drive noise, coast noise or float noise.
a. Ring
and pinion gear noise.
b. Front
pinion bearing noise, coast or drive.
c. Axle bearing noise.
10. Clunk
on
acceleration or deceleration.
a. Worn
rear axle pinion shaft splines.
b. Side
gear hub counterbore in case worn
oversize.
c. Worn U-joints.
d. Excessive transmission backlash.
e. Worn axle shaft splines.
11. Chatter on turns.
a. Wrong
lube in rear axle.
b. Clutch
cone worn or spalled.
12. Clunk
or knock on rough road operation.
a. Worn suspension bushings.
PRE-REPAIR INVESTIGATION AND TROUBLE
DIAGNOSIS
A carefull diagnosis of the rear axle prior to
disassembly will often reveal valuable information as to
the extent and type of repairs or adjustments necessary.
Since frequent causes of axle noises are improper
backlash, pinion bearing pre-load, or side bearing
pre-load, or a combination, a few simple adjustments
may be all that are necessary to correct a problem.
Before disassembling the rear axle, the following
checks should be made with the results recorded and
analyzed: 1) Backlash;
2) Total Assembly Preload; 3)
Tooth Contact Pattern Test; 4) Fluid Level; and 5)
Fluid Contamination.
If axle shaft end play is excessive then check
bearings, retainer, and bolts securing backing plate.
The axle bearings could be worn and need replacement.
The four bolts or nuts securing the brake backing plate
may be loose, stripped, or missing. If the inner bearing
retainer worked loose it must be replaced.
Use care at all times to keep dirt and other foreign
matter, such as grinder dust, soot or sand, away from
differential to prevent possibility of subsequent failure.

REAR AXLE 4B1-5
CONSIDER THE FOLLOWING FACTORS WHEN DIAGNOSING BEARING CONDITION
I 1. GENERAL CONDITION OF ALL PARTS DURING DISASSEMBLY AND INSPECTION I
I 2. CLASSIFY THE FAILURE WITH THE AID OF THE ILLUSTRATIONS. I
I 3. DETERMINE THE CAUSE I
I 4. MAKE ALL REPAIRS FOLLOWING RECOMMENDED PROCEDURES I
GOOD BEARING
I
BENT CAGE
I BENT CAGE I
I
CAGE DAMAGE DUE TO IMPROPER CAGE DAMAGE DUE TO IMPROPER
HANDLING OR TOOL USAGE.
I HANDLING OR TOOL USAGE.
GALLING
METAL SMEARS ON ROLLER ENDS DUE
TO OVERHEAT. LUBRICANT FAILURE OR
OVERLOAD.
REPLACE BEARING
- CHECK SEALS AND
CHECK FOR PROPER LUBRICATION. REPLACE
BEARING.
1 ABRASIVE STEP WEAR
1 PATTERN ON ROLLER ENDS CAUSED BY FINE ABRASIVES
CLEAN ALL PARTS AND HOUSINGS,
CHECK SEALS AND BEARINGS AND
REPLACE IF LEAKING, ROUGH OR
NOISY. ETCHING
BEARING SURFACES APPEAR GRAY OR
GRAYISH BLACK IN COLOR WITH RELATED ETCHING AWAY OF MATERIAL
USUALLY AT ROLLER SPACING.
REPLACE BEARINGS
- CHECK SEALS
AND CHECK FOR PROPER LUBRICATION.
I
MISALIGNMENT
I
INDENTATIONS
I
FATIGUE SPALLING
I OUTER RACE MISALIGNMENT DUE TO
FOREIGN OBJECT. I
CLEAN RELATED PARTS AND REPLACE
BEARING. MAKE SURE RACES ARE
PROPERLY SEATED. OF
FOREIGN MATERIAL.
REPLACE BEARING - CLEAN ALL
CHECK SEALS AND REPLACE BEARING
Fig. 2 Rear Axle Bearing Diagnosis

4B1-6 REAR AXLE
THE BEARING IS NOT ROTATING.
SEALS AND REPLACE BEARINGS. CHECK SEALS AND BEARINGS AND
CRACKED INNER RACE
F R ETTAGE
OVERLOADS OR HANDLING DAMAGE.
AND LUBRICATION.
HEAT DISCOLORATION CAN RANGE
FROM FAINT YELLOW TO DARK BLUE
RESULTING FROM OVERLOAD OR
INCORRECT LUBRICANT.
EXCESSIVE HEAT CAN CAUSE
SOFTENING OF RACES OR ROLLERS.
STAIN DISCOLORATION
TEMPERED PART
WILL GRAB AND CUT
WITH NO METAL CUTTING. NO EVIDENCE OF OVERHEATING IS
Fig. 3 Rear Axle Bearing Diagnosis

REAR AXLE 481-7
ON-VEHICLE SERVICE
CARRIER COVER AND GASKET
Remove or Disconnect
1. Having
a container in place remove drain plug
with tool
J-35117,remove cover bolts and pry
cover loose to drain lubricant.
2. Make sure both
gasket sealing surfaces are clean.
Install or Connect
Use cover gasket (do not assemble with
sealant alone).
NOTICE: Apply locktite part No. 573, GM Part
Nos. 1052080, or 1052279 or equivalent to cover
bolts before installing cover. If sealant is not applied
bolts may loosen causing fluid leak and damage to
rear axle assembly.
1. Torque cover bolts in a crosswise pattern to
insure uniform draw on gasket. Torque
26 N.m
(20 1b.ft.).
2. Fill with lubricant to bottom of filler plug hole.
Refer to specifications for correct lubricant usage
and quantity.
AXLE SHAFT
Remove or Disconnect
1. Wheel
and brake components as necessary.
2. The
four nuts holding the brake anchor plate and
outer bearing retainer.
3. Withdraw the axle shaft and wheel bearing assem-
bly using axle shaft remover
J 21579 and slide
hammer
J 2619-01 (Fig. 4).
Fig. 4 Axle Shaft Removal
4. Inner
bearing retainer and bearing from axle
shaft. To do this carefully split the retainer with
a chisel and remove from shaft. Press off bearing
with tool
5-22912-01 from axle. Discard bearing
and seal (Fig. 5).
Fig. 5 Bearing and Seal Removal
Examine axle shaft. If axle shaft is in satisfactory
condition it may be re-used.
Important
Bearings and inner bearing retainers which
have been removed from an axle shaft
should not be re-used.
Install or Connect
1. Place the outer bearing retainer on the axle shaft.
Important
Right and left hand axle shaft seals are
different in construction. Right hand seal is
black banded with right hand ridges. Left
hand seal is gold banded with left hand
ridges. The part numbers designate left and
right sides.
2. Place the oil seal on the axle shaft ensuring that
the spring side of the oil seal faces the center of
the axle. Lubricate seals lips with a light coat of
grease. Note use of excessive amounts of grease
may damage seal.
3. Press wheel bearing and inner bearing retainer hard
against bearing shoulder on axle shaft with tool
J 8853-01, ensuring that the retainer is tight against
the bearing and with
O.D. chamfer towards
bearing.
4. Place the axle shaft through the brake anchor
plate and align axle shaft and side gear splines.
5. Once the splines have been engaged in the side
gears the wheel bearing and oil seal may be
pushed into the housing.
A light coat of grease on
the seal outside diameter will assist in installation.
Tighten four backing plate bolts alternately. Use
new locknuts on bolts. (Refer to specifications).
NOTICE: If a limited-slip differential is used
ensure that both axle shaft splines are fully
engaged before the axle shafts are rotated. This is
to mainatain spline alignment, refer to limited-slip
instructions.

481.8 REAR AXLE
6. Replace
brake components and wheel.
7. Tighten wheel nuts and lower vehicle.
Tooth Contact Pattern Test
The side of the ring gear tooth which curves
outward, or is convex, is referred to as the "drive" side.
The concave side is the "coast" side. The end of the
tooth nearest center of ring gear is referred to as the
"toe" end. The end of the tooth farthest away from the
center is the "heel" end. Toe end of tooth is smaller
than heel end.
It is very important that tooth contact be tested
before the rear axle carrier assembly is disassembled.
Variations in the carrier or pinion rear bearing may
cause the pinion to be too far away from, or close to,
the ring gear. Thus, the tooth contact must be tested
and corrected, if necessary, or the gears may be noisy.
Procedure
1. Drain
oil out of carrier and carefully clean each
tooth of ring gear.
2. Apply parking brake until a torque of 54 to 70
N-m (40-50 lb. ft.) is required to turn the pinion.
3. Tighten bearing cap bolts to 52 N-m (40 lb. ft.).
4. Use gear marking compound part number
1052351 or equivalent and apply this mixture
sparingly to all ring gear teeth, using a medium
stiff brush. When properly used, the area of
pinion tooth contact will be visible when hand
load is applied.
A test made without loading the gears will not
give a satisfactory pattern. Turn pinion flange
with wrench so that ring gear rotates five full
revolutions, then reverse rotation so that ring
gear rotates five
revolutio~ls in opposite direction.
5. Observe pattern on ring gear teeth and compare
with Fig.
6.
Effects of Increasing Load on Teeth Contact
Pattern
When "load" on ring and pinion gear is
increased, such as when car is accelerated forward
from standstill or from normal drive, the tooth contact
will tend to spread out and, under very heavy load, will
extend from near toe to near heel on the drive side. The
entire contact also tends to shift toward heel under
increasingly heavier loads and will become somewhat
broader with respect to tops and bottoms of teeth. The
patterns obtained by this tooth contact pattern test
approximate a light load and, for this reason, they will
extend only about halfway.
The important thing to note is that the contact
pattern is centrally located up and down on the face of
the ring gear teeth.
Adjustments Affecting Tooth Contact
Two adjustments can be made which will affect
tooth contact pattern, backlash and position of drive
pinion in carrier. The effects of bearing pre-loads are
not readily apparent
on (hand-loaded) tooth contact
pattern tests; however, these adjustments should be within
specifications before proceeding with backlash
and drive pinion adjustments.
Backlash is adjusted by means of the side bearing
adjusting shims, which moves the entire case and ring
gear assembly closer to, or farther from, the drive
pinion (the adjusting shims are also used to set side
bearing pre-load). The position of the drive pinion is
adjusted by increasing or decreasing the shim thickness
between the rear pinion cup and axle housing
. The
shim is used in the rear axle case to compensate for
manufacturing tolerances. Increasing shim thickness
will move the pinion closer to centerline of the ring
gear. Decreasing shim thickness will move pinion
farther away from centerline of the ring gear.
Effects of Pinion Position on Tooth Pattern
When the drive pinion is too far away from
centerline of the ring gear, the pattern will be a high
heel contact on the drive side and high toe contact on
coast side (Fig. 6). Moving the pinion closer to
centerline of the ring gear by increasing shim thickness
will cause the high heel contact on drive side to lower
and move toward the toe; the high toe contact on coast
side will lower and move toward the heel.
When the pinion is too close to the centerline of
the ring gear, the pattern will be a low toe contact on
drive side and a low heel contact on the coast side.
Moving the pinion farther away from the ring gear by
decreasing shim thickness will cause low toe contact on
drive side to raise and move toward the heel; the low
heel contact on coast side will raise and move toward
the toe.
PINION OIL SEAL AND COMPANION FLANGE
REPLACEMENT
Remove or Disconnect
1. Mark the propeller shaft and companion flange
so they can be reassembled in the same position.
Remove four nuts and lock washers from two
saddles retaining
U-joints to companion flange
and remove propeller shaft.
2. Measure and record preload at pinion - this
includes pinion bearing, differential bearings,
effect of grease and oil seal. (Figure
7).
3. Pinion nut with companion flange remover
J-8614-01. (Figure 8).
4. Companion flange with companion flange
remover
5-8614-01. (Figure 8).
5. Seal and discard.
NOTICE: Before installing a new seal examine the
surface of the companion flange on which the seal
runs. Should this surface be damaged or the splines
excessively worn, a new companion flange should
be installed. Also examine the housing bore and
remove any nicks or burrs.

REAR AXLE 481-9
A central face lengthwise position is shown here representing
COAST SlDE the limit of acceptability of the contacts position towards DRIVE SIDE the heel.
ACCEPTABLE HEEL
CONTACTS
DRIVE SlDE COAST
SlDE
HEEL END
The contact should fade out at least 5mrn before the heel
end face,
A central profile position is shown and is acceptable alrhough a low contact is preferred.
The center of the contact is located at
518 of the face width
from the toe and it does not approach the heel end by less
than
5mm,
A high contact pattern as shown is preferred for coast side
contacts which tend to be towards the heel.
A central profile position is acceptable providing pinion face
angle edge lines do not appear low on the gear.
The contact begins almost at the toe end face and extends in
length by approx, half the facewidth.
A slightly lower contact pattern as shown is preferrable although a centrally located profile postion will suffice.
The contact begins almost at the toe end face and may appear
pointed as shown although a square end is equally acceptable.
The total length of contact is approx.
112 of the face width.
A high profile position is desirable although a central profile
is acceptable.
IDEAL
CONTACTS
DRIVE SIDE COAST SIDE A central toe lengthwise position and a slightly lower contact
pattern in the profile position. Total length about 518 of gear
facewidth.
Note the clearance of about
1 rnrn between the contact and the
toe and along the top face angle line.
A centrally located lengthwise position and a slightly higher
contact pattern in the profile position. Total length about
518 of the gear facewidth.
Note the clearance between the contact and the face angle line
of the gear.
ACCEPTABLE
TOE CONTACTS
Fig. 6 Gear Tooth Contact Pattern

481-10 REAR AXLE
LB. IN. TORQU
520021-481
Fig. 7 Bearing Preload Measurement
Fig.
8 Companion Flange Removal
Install or Connect
1. Lubricate oil seal lips with a light cover of grease.
2. Install
new seal in carrier, flush to
0.25mm (0.
010) below surface with pinion seal installer
5-351 19. (Fig. 9).
Fig. 9 Pinion Seal Installation
3. Companion flange and tighten nut to achieve the
bearing preload as measured in Step
2 above plus
0.5
N-m (5 lb. in.) to allow for the new seal with
companion flange installer J-86 14-0 1 (Fig.
8).
NOTICE: If pinion nut is over tightened by more
than 0.5
N.m (5 lb. in.) as in step 3 then the unit
should be rebuilt with a new collapsible spacer as
in step 3.
4. Align propeller shaft on locating marks and
connect propeller shaft with 2
U saddles and 4
bolts and lockwashers to companion flange.
5. Fill with lubricant to bottom of filler plug hole.
Refer to specifications for correct lubricant usage
and quantity.
6. Filler plug.
REAR WHEEL BOLT
Remove or Disconnect
1.
Raise vehicle on hoist allowing axle to hang
freely.
2. Wheel, tire and caliper and rotor.
3. Using Tool J 6627-A press out stud (Fig. 10).
Fig. 10 Removing Wheel Stud
I Install or Connect
1. Place new stud in axle flange hole. Slightly start
stud serrations in hole by firmly pressing back of
stud with your hand.
2. Place a flat washer on the stud and install a lug
nut with flat side first (tapered face outboard).
Tighten on lug nut drawing stud into flange until
stud head is bottomed on back side of flange. (Fig.
11).
3. Remove lug nut.
4. Rotor and caliper, wheel and tire.
5. Lower vehicle and remove from hoist.
REAR AXLE ASSEMBLY
It is not necessary to remove the rear axle
assembly for any normal repairs. However, if the
housing is damaged, the rear axle assembly may be
removed and installed using the following procedure.
I Remove or Disconnect .I
1. Hoist car and support at frame. Hoist must
remain under rear axle housing.
2. Wheels and lug nuts.

REAR AXLE 4Bl-I I
Fig. 11 Installing Wheel Bolt
Loosen parking brake cable adjuster nut and
remove two parking brake cables from adjuster
and body clips.
Shock absorbers from axle.
Track bar from rear axle and body.
Stabilizer bar links from axle and bushings.
Mark propeller shaft and companion flange, then
disconnect and remove propeller shaft.
Brake line junction block bolt at axle housing,
then disconnect brake lines at wheel cylinders.
Brake lines from clips.
Lower rear axle and remove springs.
Torque arm from rear axle.
Lower control arms from rear axle.
Lower hoist and remove rear axle assembly from
vehicle.
Install or Connect
Raise hoist and rear axle assembly.
Lower control arms to rear axle.
Torque arm to rear axle.
Springs and raise rear axle assembly.
Brake lines to clips.
Brake line junction block bolt at axle housing,
then connect brake lines at wheel cylinders or
calipers.
Align drive shaft and pinion flange, then install
drive shaft and connect.
Stabilizer bushings and links to axle.
Track bar to body and rear axle.
Shock absorbers to axle.
Parking brake cables to body clips and cable
adjuster, then tighten parking brake cable
adjuster nut.
Wheels and tighten lug nuts.
Frame supports and lower hoist.
NOTICE: Lubricant level is to the bottom of the
filler plug hole. Use only the specified lubricant.
(Refer to Specifications).
Before attempting any service procedures the
technician must know what type rear axle is to be
serviced. Refer to chart (Rear Axle Codes And
Identification) to identify codes, ring gear size, and ratios.
Remember that all ring gear bolts have
L.H.
threads.
Most rear axle service repairs can be made by
supporting the car by the frame with the axle housing
supported and lowered to its lowest travel. On some
models it may be necessary to disconnect shock
absorbers to obtain additional clearance. When doing
this, do not allow the rear brake hose to become
kinked
or stretched.
Lubricant may be drained by backing out all
cover bolts and breaking cover loose at the bottom.
If the rear axle housing is removed for any reason,
rear axle service can be performed on the bench.
When a new ring gear and pinion is installed, the
owner should be advised not to accelerate rapidly or
exceed 50 mph for the first 50 miles of driving.
It is necessary to perform a service diagnosis
before disassembly of the rear axle. Check all fasteners
with torque wrench for correct torque. Check level and
condition of fluid.
If fluid is contaminated the rear axle
will require disassembly and a complete inspection and
cleaning. The bearing preloads should be checked with
a torque wrench. A dial indicator reading should be
made for run out of ring gear and backlash between
ring and pinion gear. Use specifications from chart
below to perform suggested diagnostic checks. Roll
gears and paint to read out pattern.
DRAIN REAR AXLE ASSEMBLY
1. Loosen cover and pry cover away from carrier.
2. Let axle fluids drain from carrier.
3. Remove cover bolts and cover from carrier.
4. Scrape off gasket and sealer from cover and
carrier.
Remove or Disconnect
Differential Assembly
1. Bearing caps and bolts. Identify bearing caps with
paint. The bearing caps are not interchangeable.
2. The differential assembly is worked out of the
carrier by putting a box wrench on ring gear bolt.
The box wrench contacts back of housing when
companion
tlange is rotated with tool 3-8614-01.
When the differential assembly rotates out of the
carrier from pinion rotation the shims will also
come out. The shims and bearing caps location,
left or right, must be identified for reassembly.
(Fig. 12).
3. Differential assembly from carrier.
Remove or Disconnect
Hypoid Pinion and Pinion Bearings
1. Pinion nut and companion flange from pinion
with companion flange tool 5-8614-01. (Fig. 8).
2. Drive pinion gear through rear of carrier with
soft face hammer.