1988 PONTIAC FIERO check engine

4A-4 PROPELLER SHAFT
PROPELLER SHAFT BALANCING
Hose Clamp Method
Figures 4A- 1 1 thru 4A-13
1. Place the vehicle on a twin post hoist so that the
rear of the vehicle is supported on the rear axle
housing and the rear wheels are free to rotate.
Remove both rear wheel assemblies and reinstall
wheel lug nuts with flat sides next to
drums/discs.
2. Mark and number propeller shaft at four (4)
points 90 degrees apart at rear of shaft just
forward of balance weight, as shown.
3. Install two (2) hose clamps on the rear of the
propeller shaft and slide them rearward until the
clamps stop at the nearest balance weight welded
to the tube. Align both clamps at any one of the
four marks made on shaft in Step 2 and tighten.
Be sure sufficient clearance is maintained so that
clamp heads do not contact floor pan of vehicle
when axle is in contact with rebound bumper in
frame. In order to gain sufficient clearance, it
may be necessary to position the clamps over the
balance weights.
4. Run the vehicle through the speed range to 80-90
MPH (130-145
Km/h) and note amount of
imbalance.
CAUTION: All persons should stay
clear of universal joint and balance
weight areas to avoid possible injury.
Do not run on hoist for extended
periods due to the danger of
overheating the transmission or
engine.
5. Loosen clamps and rotate clamp heads 90 degrees
to the next mark on a propeller shaft. Tighten
clamps and repeat Step 4.
6. Repeat Step 5 until car has been run with clamp
heads located at all four marks on shaft.
7. Position clamps at point of least imbalance.
Rotate the clamp heads away from each other 45
degrees (one on each side of the position), as
shown. Run the vehicle and note if imbalance has
improved.
In some cases it may be necessary to use one
clamp or possibly three clamps in order to obtain
a good balance. Replace shaft if three hose clamps
do not improve the imbalance.
8. Continue to rotate the clamps apart in smaller
angular increments until the imbalance is at its
minimum.
9. Reinstall wheel assemblies and road test the
vehicle for final check of balance. A minimal
vibration felt in the vehicle on the hoist may not
show up during a road test.
Strobe Light Method
Figures 461- 1 1, $A- 14, and 4A- 15
If a wheel balancer of the strobe light type is
available, the use of such a unit will facilitate the
balancing of the propeller shaft. The balance pick-up
unit should be placed directly under the nose of the
rear axle carrier and as far forward as possible. 1.
Place
the vehicle on a twin post hoist so the rear of
the vehicle is supported on the rear axle housing and
the rear wheels are free to rotate. Lower rear hoist
and allow axle to rest on jackstands. The groove in
the rear hoist fixture could clamp the axle and de-
stroy the sensitivity of the operation. Remove both
rear wheel assemblies and reinstall wheel lug nuts
with flat sides next to the
drums/rotors.
2.
Mark and number drive shaft at 4 points 90
degrees apart at rear of shaft just forward of
balance weights, as shown.
3. Place the strobe light wheel balancer pick-up
under the nose of the carrier.
4. Run vehicle in gear at the speed where the
distrubance is at its peak, allow the driveline to
stabilize by holding at a constant speed. Point
strobe light up at the spinning propeller shaft and
note position of one of the reference numbers.
Shut off engine and position the propeller shaft so
the reference numbers will be in the same position
as was noted while the shaft was rotating.
When strobe light flashed, the heaviest point of
the shaft was at the bottom (6 o'clock). To
balance the propeller shaft, it would be necessary
to apply the balancing weights (hose clamps) 180
degrees away from the heaviest point or at the top
of the propeller shaft (12 o'clock).
5. Install two screw-type hose clamps on the
propeller shaft as close to the rear as possible.
Position both clamp heads 180 degrees from the
heaviest point of drive shaft as indicated by strobe
light. Tighten clamps.
NOTICE: Be sure sufficient clearance is
maintained so clamp heads do not contact floor
pan of vehicle when axle is in contact with rebound
bumper on frame. In order to gain. sufficient
clearance, it may be necessary to position the
clamps over the balance weights.
6. Run vehicle through the speed range 80-90
M.P.
H. (130-145 Km/h). If disturbance is gone,
nothing further need be done on the hoist. If the
disturbance is not gone and the strobe light shows
the clamp heads at the bottom (6 o'clock) of the
shaft, go to Step
7. If the strobe light shows the
two clamp heads at the top of the shaft, add one
more hose clamp and recheck. If the strobe light
shows the three clamp heads at the top of the
shaft, remove the propeller shaft and
reindex it
180 degrees on the rear axle pinion companion
flange. Recheck with no clamps. Repeat balance
starting with Step 5. If the shaft still needs more
than three hose clamps at the same clock position,
replace it. If the clamps are also 180 degrees from
their original position after the propeller shaft
was reindexed 180 degrees, the rear axle pinion
companion flange is out of balance and must be
replaced. DO NOT use more than three hose
clamps to balance the shaft. If the strobe light
shows the hose clamps at the bottom of the shaft,
but the disturbance still exists, go to Step
7.

4819 REAR AXLE
bears against the inner race of the front bearing and a
shoulder on the pinion stem. This spacer is used to
enable accurate bearing pre-load adjustment and
maintain a pre-load on both front and rear pinion
bearings, Adjustment of the fore and aft position of the
pinion is obtained by placing a shim between the rear
pinion bearing cup and axle housing. The differential
case is of two-piece construction and is supported in
the carrier by two tapered roller side bearings. Pre-load
rear axle case by inserting shims between the bearings
and the carrier. The rear axle case assembly is
positioned for proper ring gear to pinion backlash by
varying the shim thickness from side to side. The ring
gear is bolted to the case. Two side gears have splined
bores for driving the axle shafts. They are positioned
to turn in counterbored cavities in the case. The four
rear axle pinions have smooth bores and are held in
position by a pinion cross shaft, mounted and locked
in the rear axle case. All six gears are in mesh with each
other and because the pinion gears turn freely on their
shaft, they act as idler gears when the rear wheels are
turning at different speeds. The pinions and side gears
are backed by steel thrust washers.
LIMITED-SLIP REAR AXLE
The operation of the Limited-Slip differential is
the same as the standard differential, except that there
is additional friction provided by the conical clutches.
Under ordinary driving and cornering conditions, the
cones slip, allowing the outside wheel to turn faster
than the inner. Under poor traction conditions, such as
ice, snow, or loose gravel under one driving wheel, the
increased friction provided by the cones increases the
driving torque available to the wheel with the better
traction. The cones are spring loaded to provide the
increased driving torque under extremely low traction
conditions.
Operation
When the vehicle turns a corner, the outer rear
wheel must turn faster than the inner wheel. The inner
wheel, turning slower than the outer wheel, slows its
differential side gear (as the axle shaft is splined to the
side gear) and the differential pinion gears will roll
around the slowed differential side gear, driving the
other differential side gear and wheel faster.
DIAGNOSIS AND TESTING
Many noises reported as coming from the rear
axle assembly actually originate from other sources
such as tires, road surfaces, front wheel bearings, axle
bearing, engine, transmission, muffler or body
drumming. A thorough and careful check should be
made to determine the source of the noise before
disassembling the rear axle. Noise which originates in
other places cannot be corrected by adjustment or
replacement of parts in the differential. It should also
be remembered that rear axle gears, like any other
mechanical device, are not absolutely quiet and should
be accepted as being commercially quiet unless some
abnormal noise is present.
To make a systematic check for axle noise under
standard conditions, observe the following:
1. Select a level smooth asphalt road to reduce tire
noise and body drumming.
2. Check rear axle lubricant to assure correct level,
then drive car far enough to thoroughly warm up
rear axle lubricant, approximately 10 miles.
3. Note speed and RPM at which noise occurs. Stop
car and put transmission in neutral. Run engine
slowly up and down through engine speeds,
corresponding to car speed at which noise was
most pronounced, to determine if it is caused by
exhaust, muffler roar or other engine conditions.
4. Tire noise changes with different road surfaces,
but rear axle noise does not. Temporarily
inflating all tires to approximately 50 pounds
pressure
for test purposes only will materially
alter noise caused by tires, but will not affect noise
caused by rear axle. Rear axle noise usually stops
when coasting at speeds under 30 miles per hour;
however, tire noise continues, but with lower
tone, as car speed is reduced. Rear axle noise
usually changes when comparing acceleration
and coast, but tire noise remains about the same.
Distinguish between tire noise and rear axle noise
by noting if noise varies with various speeds or
sudden acceleration and deceleration; exhaust
and axle noise show variations under these
conditions while tire noise remains constant and
is more pronounced at speeds of 20 to 30 miles
per hour. Further check for tire noise by driving
car over smooth pavements or dirt roads (not
gravel) with tires at normal pressure. If noise is
caused by tires, it will noticeably change or
disappear and reappear with changes in road
surface.
5. Loose or rough front wheel bearings will cause
noise which may be confused with rear axle
noises; however, front wheel bearing noise does
not change when comparing drive and coast.
Light application of brakes while holding car
speed steady will often cause wheel bearing noise
to diminish, as this takes some weight off the
bearing. Front wheel bearings may be easily
checked for noise by jacking up the wheels and
spinning them, also by shaking wheels to
determine if bearings are loose.
6. Rear suspension rubber bushings and spring
insulators dampen out rear axle noise when
correctly installed. Check to see that no metallic
contact exists between the spring and spring seat
opening in frame or between upper and lower
control arm bushings and frame or axle housing
brackets. The track bar and torque arm must be
bolted securely. Metal-to-metal contact at those
points may result in telegraphing road noise and
normal axle noise which would not be
objectionable if dampened by bushings.
AXLE NOISES
After the noise has been determined as being in
the axle by following the above appraisal procedure,
the type of axle noise should be determined to aid in
making repairs if necessary.

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.

4B1-12 REAR AXLE
NOTICE: Mark differential case halves with
alignment mark before disassembly because they
could be assembled
180" off from original position.
Fig. 12 Differential Assembly Removal
3. Pry front seal out of carrier and remove bearing
cone. Discard seal.
4. Rear pinion bearing with tool J 21493-B and
press. Clamp tool around pinion shaft holding
bearing and press pinion shaft off rear pinion
bearing. (Fig. 13).
I
5. Drive rear bearing cone out of carrier with soft
brass drift, and remove selective spacer washer.
Remove or Disconnect
Four Pinion Standard Differential Assembly
(Figure
14)
1. Ring gear bolts.
1 Important
MCTICE: Left hand thread ring gear bolts.
2. Ring gear from differential housing, with soft face
hammer.
3. Drive out three differential pinion cross shaft
retaining pins.
4. Drive three differential pinion shafts from
housing, long shaft first.
5. Split differential case by holding one side and
tapping against other side with long soft drift.
6. Four differential pinions, side gears and thrust
washers from housing.
7. Differential case bearings with tool 5-22888-D
(Fig. 15).
Inspection
All components should be cleaned and inspected
for excessive wear.
Cleaning of bearings should be performed with
new solvent and should be followed up by coating
the bearing with light engine oil
to prevent
rusting.
1. I-Iypoid gear set
Important
a.
Examine for scuffed or chipped teeth. A
gear set cannot be made to run quiet if teeth
are scuffed.
b. Ring gear bore and back face should be
clean and free from burrs. The rear bearing
preload abutment faces on the
hypoid
pinion should be clean and free from burrs.
c. Examine the thread and bearing journal of
the
hypoid pinion.
2. Bearings
Important
a. Cups should have an even wear pattern and
be free from flaking or pitting. Ensure that
the abutment faces are clean and free from
burrs or raised metal.
b. The cone assemblies should feel smooth
when turned in the cups.
c. The assembly should be free from loose
particles. No cracks should be present in the
roller cages and the bores should contain no
tears.
3. Differential pinions and side gears.
Important
a. Examine the teeth for cracks and hard
contact marks. It is advisable to check the
teeth for cracks and excessive wear. The
side gear splines should be checked for
excessive wear.
b. Check the side gear journals and back thrust
for scoring.
c. The
differential pinion bores and spherical
thrust surfaces should be smooth and free
from scores.
4. Thrust washers should be free from cracks, nicks
or burrs.
5. Differential pinion cross shafts cannot be bent
and the pinion gear mating surfaces must not be
scored.

REAR AXLE 4B-1
SECTION 4B
REAR AXLE
NOTICE: All rear axle attaching fasteners are an necessary.
Do not use a replacement part of lesser
important part in that they could affect the quality
or substitute design. Torque values must
performance of vital parts and systems, and/or be
used as specified during reassembly to assure
could result in major repair expense. They must proper retention
of all parts. (There is to be no
be replaced with one of the same part number or welding
as it may result in extensive damage and
with an equivalent part if replacement becomes weakening
of the metal.)
CONTENTS
General Description .................................. 4B-1
Standard Rear Axle ................... .. ............ 4B- 1
Diagnosis and Testing ............................... 4B-1
Axle Noises ......................... .. ................ 4B-3
Gear Noise ...................... .. .................. 4B-3
Bearing Noise ........................................ 4B-3
Rear Wheel Bearing Noise ....................... 4B-3
Knock at Low Speeds ............................. 4B-3
Backlash Clunk ...................................... 4B-3
Rear Axle Standard and Limited Slip .......... 4B-3
Pre-Repair Investigation and Trouble
Diagnosis
................................................. 4B-4
Gear Tooth Nomenclature ....................... 4B-4
Tooth Contact Pattern Test ..................... 4B-4
Effects of Increasing Load on
Teeth Contact Pattern
.......................... 4B-4
Adjustments Affecting Tooth
Contact
.................................................. 4B-6
Effects of Pinion Position on Tooth
Pattern
................... ... .................... 4B-6
General information ....................... .. ..... 4B-8
Limited-Slip Rear Axle ............................... 4B-8
On-Vehicle Service ............................. .. ....... 4B-8
Carrier Cover and Gasket .......................... 4B-8
............................................. Axle Shaft 4B-8
Oil Seal and/or Bearing (With
Axle Shaft Removed)
............................. 4B-9
........................................ Pinion Oil Seal 4B-9
........................................... Pinion Flange 4B- 10
..................................... Rear Wheel Bolt 4B- 1 1
.................................................... Unit Repair 4B-1 1
..................................... Rear Axle Assembly 4B- 1 1
Disassembly of Rear Axle
............................................... Assembly 4B- 1 1
.. ..................................... Case Assembly ... 4B- 12
Drive Pinion, Bearing and Races ............. 4B- 12
............................... Bearing Replacement 4B- 12
...................... Setting Drive Pinion Depth 4B- 13
........................................ Rear Axle Case 4B- 14
Side Bearing Preload Adjustment ............ 4B- 15
.................................................. Drive Pinion 4B- 16
Rear Axle Backlash Adjustment .............. 4B- 17
........... Limited Slip Rear Axle (Cone Type) 4B-17
...................................... Auburn Cone Type 4B- 18
.............................................. Specifications 4B- 19
.............................................. Special Tools 4B-20
GENERAL DESCRIPTION
STANDARD REAR AXLE Operation
The rear axle assembly is of the semi-floating type
in which the car weight is carried on the axle housing.
The rear axle assembly is designed for use with an open
drive line and coil springs. The rear axle has a
hypoid
type ring gear and pinion with the centerline of the
pinion gear below the centerline of the ring gear.
All parts necessary to transmit power from the
propeller shaft to the rear wheels are enclosed in a When
the vehicle turns a corner, the outer rear
wheel must turn faster than the inner wheel. The inner
wheel, turning slower than the outer wheel, slows its
differential side gear (as the axle shaft is splined to the
side gear) and the differential pinion gears will roll
around the slowed differential side gear, driving the
other differential side gear and wheel faster.
DIAGNOSIS AND "TESTING
salisbury type axle housing (a carrier casting with tubes Many
noises reported as coming from the rear
pressed and welded into the carrier to form a complete axle assembly actually
originate from other sources
carrier and tube assembly). A removable steel cover such as
tires, road surfaces, wheel bearings, engine,
bolted to the rear of the carrier permits service of the transmission,
muffler or body drumming. A thorough
rear axle without removing the entire assembly from and
careful check should be made to determine the
the car. source
of the noise before disassembling the rear axle.

REAR AXLE 4B-3
Noise which originates in other places cannot be
corrected by adjustment or replacement of parts in the
differential. It should also be remembered that rear
axle gears, like any other mechanical device, are not
absolutely quiet and should be accepted as being
commercially quiet unless some abnormal noise is
present.
To make a systematic check for axle noise under
standard conditions, observe the following:
1. Select a level smooth asphalt road to reduce tire
noise and body drumming.
2. Check rear axle lubricant to assure correct level,
then drive car far enough to thoroughly warm up
rear axle lubricant.
3. Note speed and RPM at which noise occurs. Then
stop car and with automatic transmission in neutral,
run engine slowly up and down through engine speeds, corresponding to car speed at which noise
was most pronounced, to determine if it is caused by
exhaust, muffler roar or other engine conditions.
4. Tire noise changes with different road surfaces,
but rear axle noise does not. Temporarily
inflating all tires to approximately 50 pounds
pressure for
test purposes only will materially
alter noise caused by tires, but will not affect noise
caused by rear axle. Rear axle noise usually stops
when coasting at speeds under 30 miles per hour;
however, tire noise continues, but with lower
tone, as car speed is reduced. Rear axle noise
usually changes when comparing acceleration
and coast, but tire noise remains about the same.
Distinguish between tire noise and rear axle noise
by noting if noise varies with various speeds or
sudden acceleration and deceleration; exhaust
and axle noise show variations under these
conditions while tire noise remains constant and
is more pronounced at speeds of 20 to 30 miles
per hour. Further check for tire noise by driving
car over smooth pavements or dirt roads (not
gravel) with tires at normal pressure. If noise is
caused by tires, it will noticeably change or
disappear and reappear with changes in road
surface.
5. Loose or rough front wheel bearings will cause
noise which may be confused with rear axle
noises; however, front wheel bearing noise does
not change when comparing drive and coast.
Light application of brakes while holding car
speed steady will often cause wheel bearing noise
to diminish, as this takes some weight off the
bearing. Front wheel bearings may be easily
checked for noise by jacking up the wheels and
spinning them, also by shaking wheels to
determine if bearings are loose.
6. Rear suspension rubber bushings and spring
insulators dampen out rear axle noise when
correctly installed. Check to see that no metallic
contact exists between the spring and spring
opening in frame or between upper and lower
control arm bushings and frame or axle housing
brackets.
Metal-to-metal contact at those points
may result in telegraphing road noise and normal axle
noise which would not be objectionable if
dampened by bushings.
AXLE NOISES
Gear Noise
After the noise has been determined as being in
the
axle by following the above appraisal procedure,
the type of axle noise should be determined to aid in
maki~~g repairs if necessary.
Gear noise (whine) is audible from 20 to
55 mph
under four driving conditions:
1. Drive - Acceleration or heavy pull.
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. Gear
noise most frequently has periods where noise is
more prominent, usually 30 to 40 mph and 50 to
55 mph.
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.
I(noclc 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.
Baclclash Clunk
Excessive clunk with acceleration and
deceleration is caused by worn differential pinion shaft,
excessive clearance between axle shaft and side gear
splines, excessive clearance between side gear hub and
counterbore in case worn pinion and side gear teeth,
worn thrust washers and excessive drive pinion and
rear gear backlash. Remove worn parts and replace as
required, selecting close fitting parts when possible.
Adjust pinion and ring gear backlash.
REAR AXLE STANDARD AND LIMITED-SLIP
1. Noise is the same in "Drive" or "Coast".
a. Road noise.
b. Tire noise.
c. Front wheel bearing noise.

4B-4 REAR AXLE
d. Incorrect driveline angle.
Noise changes on a different type of road.
a. Road noise.
b. Tire noise.
Noise tone lowers as car speed is lowered.
a. Tire noise.
Similar noise is produced with car standing and
driving.
a. Engine noise.
b. Transmission noise.
Vibration. a. Rough rear wheel bearing.
b. Unbalanced
or damaged propeller shaft.
c. Tire unbalance.
d. Worn
universal joint in propeller shaft.
e. Incorrect driveline angle.
f. Mis-indexed propeller shaft at pinion
flange.
g. Pinion
flange
runout too great.
A knock or click approximately every two
revolutions of the rear wheel.
a. A rear wheel bearing.
Noise most pronounced on turns.
a. Rear
axle side gear and pinion noise.
A continuous low pitch whirring or scraping
noise starting at relatively low speed.
a. Pinion bearing noise.
Drive noise, coast noise or float noise.
a. Ring and
pinion gear noise.
Clunk on acceleration or deceleration.
a. Worn rear
axle pinion shaft in case or side
gear hub counterbore in case worn oversize.
b. Insufficient
lubrication on propeller shaft
slip yoke.
c. Worn U-joints on
propeller shaft. Front or
rear.
Groan in "Forward" or "Reverse".
a. Wrong
or contaminated lube in rear axle.
b. Worn bushings.
Chatter on turns.
a. Wrong
or contaminated lube in rear axle.
b. Clutch
cone worn and/or
spring(s) worn.
Clunk or knock on rough road operation.
a. Excessive end play of axle shafts to
differential cross shaft.
b. Worn bushings.
PRE-REPAIR INVESTIGATION AND TROUBLE
DIAGNOSIS
A careful1 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.
Therefore, before removing the rear axle from the
housing, 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.
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.
The pinion and ring gear must be completely
assembled, installed and all pre-load and backlash
adjustments completed prior to the start of this method
of pinion depth setting. The following procedure can
be used in place of the gage method of pinion depth
setting.
Gear Tooth Nomenclature
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.
Tooth Contact Pattern Test
1. Wipe oil out of carrier and carefully clean each
tooth of ring gear.
2. 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.
3. Tighten bearing cap bolts to 75
N.m (55 lb. ft.).
4. Expand
brake shoes using parking brake cables
until a torque of 54 to
70 N-m (40-50 lb. ft.) is
required to turn the pinion.
A test made without loading the gears will not
give a satisfactory pattern. Turn pinion flange
with wrench so that ring gear rotates one full
revolution, then reverse rotation so that ring gear
rotates one revolution in opposite direction.
5. Observe
pattern on ring gear teeth and compare
with Fig. 3.
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.

BRAKES 5-3
DIAGNOSIS AND INSPECTION
BRAKE SYSTEM TESTING
(Figures
2 through 4)
Brakes should be tested on dry, clean, reasonably
smooth and level roadway. A true test of brake performance
cannot be made if the roadway is wet, greasy or covered
with loose dirt so that all tires do not grip the road equally.
Testing will also be affected if the roadway is crowned
which would throw the weight of the car toward the wheels
on one side. If the roadway is too rough, the wheels will tend
to bounce. Test brakes at different car speeds with both light and
heavy pedal pressure, avoid locking the brakes and sliding
the tires. Locked brakes and sliding tires do not indicate
brake efficiency, because heavily braked, but turning
wheels will stop the car in less distance than locked brakes.
More tire-to-road friction is present with a heavily braked
turning tire than with a sliding tire. The brake system is designed and balanced to avoid
locking the wheels, except at very high deceleration levels.
The shortest stopping distance and best control is achieved
without brake lock-up.
Because of high deceleration capability, a firmer pedal
may be felt at higher deceleration levels.
External Conditions That Affect Brake Performance
1. Tires. Tires having unequal contact and grip on road
will cause unequal braking. Tires must be equally
inflated and tread pattern of right and left tires must
be approximately equal.
2. Car Loading. A heavily loaded car requires more
braking effort. When a car has unequal loading, the
most heavily loaded wheels require more braking
power than others.
3. Wheel Alignment. Misalignment of the wheels, par-
ticularly excessive camber and caster, will cause the
brakes to pull to one side.
4. Front Wheel Bearings. A loose front wheel bearing
BRAKE FLUID LEAKS
With engine running at idle and the transmission in neu-
tral, depress the brake pedal and hold a constant foot pres-
sure.
If the pedal gradually falls away with the constant
pressure, the hydraulic system may be leaking. Perform a
visual check to confirm any suspected leak.
Check the master cylinder fluid levels. While a slight drop
in reservoir level does result from normal lining wear, an
abnormally low level in either reservoir indicates
a leak in
the system. The hydraulic system may be leaking either
internally or externally. See "Master Cylinder Check."
Also, the system may appear to pass this test but still have
slight leakage.
If fluid levels are normal, check the vacuum booster
pushrod length. If an incorrect length pushrod is found,
adjust or replace the
pushrod. Check the service brake
pedal travel and the parking brake adjustment.
When checking the fluid levels, the master cylinder reser-
voir may be as low as
25 mm (1 inch) from the top if the front
linings are worn. This is not abnormal.
MASTER CYLINDER CHECK
These checks will help locate some master cylinder mal-
functions. Use the Brake Diagnosis Charts to help isolate
the problem if it is not found by using these tests.
1. Check for a cracked master cylinder casting or brake
fluid around the master cylinder. Leaks are indicated
only if there is at least a drop of fluid. A damp condi-
tion is not abnormal.
2. Check for a binding pedal linkage.
3. Disassemble the master cylinder and check for swol-
len or stretched piston
seal(s). If swollen seals are
found, substandard or contaminated brake fluid
should be suspected.
If contaminated, all compo-
nents should be disassembled and cleaned. All rub-
ber components should be replaced and all the pipes
should be flushed.
permits the front wheel to tilt and lose contact with the
SUBSTANDARD OR CONTAMINATED brake shoe linings causing erratic brake operation. BRAKE FLUID
WARNING LAMP OPERATION
The brake system uses a single red "BRAKE" warning
lamp located in the instrument panel cluster. When the
ignition switch is in the "START" position, the "BRAKE"
warning lamp should come on. It should go off when the
ignition switch returns to the "RUN" position.
The following conditions will activate the "BRAKE"
warning lamp:
1. Parking brake applied. The lamp should be on when
tfie parking brake is applied and the ignition switch is
"ON."
2. Pressure differential switch detects a failure. See
"Brake Pressure Differential Warning Switch" in this
section. Improper
brake fluid, mineral oil or water in the fluid may
cause the brake fluid to boil or the rubber components to
deteriorate.
If piston cups are swollen, the rubber parts have dete-
riorated. This deterioration may also be seen by swollen
wheel cylinder piston cups on the drum brake wheels or a
swollen master cylinder cover diaphragm.
If rubber deterioration is evident, disassemble all hydrau-
lic parts and wash with alcohol. Dry these parts with com-
pressed air before assembly to keep alcohol out of the
system. Replace all rubber parts in the system, including
hoses. Check for fluid on the linings. If excessive fluid is
found, replace the linings.
If master cylinder piston seals are satisfactory, check for
leakage or excessive heat conditions. If condition is not
found, drain fluid, flush with brake fluid, fill and bleed the
system.