1988 PONTIAC FIERO Service Repair Manual

48-16 REAR AXLE
4.32mm (.170") SERVICE WACER
TOTAL THICKNESS OF TOTAL THICKNESS OF
BOTH PROD. SHIMS SERVICE SHIMS TO BE
REMOVED USED AS A STARTING POINT
Fig. 6 13 Shim Thickness
makes contact with the carrier bore so as to
obtain a correct reading. The point just before
additional drag begins is correct feeler gage
thickness. Rotate case while using feeler gage to
assure an even reading.
The original light drag is caused by weight of the
case against the carrier while additional drag is
caused by side bearing pre-load. By starting with
a thin feeler gage, a sense of "feel" is obtained so
that the beginning of pre-load can be recognized
to obtain Zero clearance. It will be necessary to
work case in and out and to the left in order to
insert the feeler gage.
6. Remove left bearing cap and shim from carrier.
The total shim pack needed (with no pre-load on
side bearings) is the feeler gage reading found in
Step
5 plus thickness of shims installed in Step 4.
7. Select two shims of approximately equal size
whose total thickness is equal to the value
obtained in Step
5. These shims will be installed
between each side bearing race and service spacer
when the case is installed in the carrier. The
object of Step 7 is to obtain the equivalent of a
"slip fit" of the case in the carrier. For
convenience in setting backlash, the pre-load will
not be added until the final step.
8. If the pinion is in position, install the ring gear,
then proceed to Rear Axle Backlash Adjustment.
DRIVE PINION
Install or Connect
1.
Install NEW collapsible spacer on pinion and
position assembly in carrier. Lubricate pinion
bearings with Rear Axle Lubricant before
installing pinion.
NOTICE: There are two types of collapsible
spacers. The conventional collapsible spacer is
used on the
7-1/2" and 8-1/2" axles. The new
inverted type is used only on the
7-5/8" axle.
Fig. 6 14 Installing Differential Adjusting Shims
COLLAPSIBLE DRIVE SPACER PINION I
Fig. 61 5 Collapsible Spacer on Drive Pinion
2.
Hold forward on pinion in case assembly.
3. Install front bearing on pinion and drive bearing
on pinion shaft until seated in race.
4. Position pinion oil seal in carrier. Install seal.
5. Coat lips of pinion oil seal and seal surface of
pinion flange with Lubricant No. 1050169 or
equivalent. Install pinion flange on pinion by
tapping with a soft hammer until a few pinion
threads project through flange.
6. Install pinion washer and nut. Hold pinion
flange, while intermittently rotating pinion to
seat pinion bearings. Tighten pinion flange nut
until end play begins to be taken up.
When no further end play is detectable and when
holder will no longer pivot freely as pinion is
rotated, pre-load specifications are being

REAR AXLE 48-1 7
approached. No further tightening should be
attempted until the pre-load has been checked.
7. Check pre-load by using an inch pound torque
wrench.
NOTICE: After pre-load has been checked, final
tightening should be done very carefully. For
example, if when checking, pre-load was found to
be 0.6
N-m (5 lbs. in.), any additional tightening
of the pinion nut can add many additional pound
inch of torque. Therefore, the pinion nut should be
further tightened only a little at a time and the
pre-load should be checked after each slight
amount of tightening. Exceeding pre-load
specifications will compress the collapsible spacer
too far and require the installation of a new
collapsible spacer.
While observing the preceeding note, carefully set
pre-load at 2.7 to 3.6
N-m (24 to 32 1b.in.) on new
bearings or 1.0 to 1.4
N m (8 to 12 1b.in.) on used
bearings.
8. Rotate pinion several times to assure that
bearings have been seated. Check pre-load again.
If pre-load has been reduced by rotating pinion,
reset pre-load to specifications.
Rear Axle Backlash Adjustment
1. Install rear axle case into carrier, using shims as
determined by the side bearing pre-load
adjustment.
2. Rotate rear axle case several times to seat
bearings, then mount dial indicator. Use a small
button on the indicator stem so that contact can
be made near heel end of tooth. Set dial indicator
so that stem is in line as nearly as possible with
gear rotation perpendicular to tooth angle for
accurate backlash reading.
3. Check backlash at three or four points around
ring gear. Lash must not vary over
.05mm (.002")
around ring gear. Pinion must be held stationary
when checking backlash. If variation is over
.05mm (.002") check for burrs, uneven bolting
conditions or distorted case flange and make
corrections as necessary.
4. Backlash at the point of minimum lash should be
between .13 and
.23mm (.005" and ,009") for all
new gears.
5. If backlash is not within specifications, correct by
increasing thickness of one shim and decreasing
thickness of other shim the same amount. This
will maintain correct rear axle side bearing
pre-load.
For each
.03mm (.001") change in backlash
desired, transfer
.05mm (.002") in shim
thickness. To decrease backlash
.03mm (.00lU),
decrease thickness of right shim .05mm (.002")
and increase thickness of left shim .05mm (.
002 "). To increase backlash .05mm (.002 ")
increase thickness of right shim .10mm (.004")
and decrease thickness of left shim .10mm (.
004"). 6.
When backlash is correctly adjusted, remove both
bearing caps and both shim packs.
Keep packs in their respective position, right or
left side.
Select a shim
.10mm (.004") thicker than the one
removed from the left side, then insert left side
shim pack between the spacer and the left bearing
race. Loosely install bearing cap.
7. Select a shim
.10mm (.004") thicker than the one
removed from right side and insert between the
spacer and the right bearing race. It will be
necessary to drive the right shim into position
(Fig. 614).
8. Torque to 75 Nem (55 1b.ft.).
9. Recheck backlash
and correct if necessary.
10. Install axles (See Rear Axle Installation).
11.
Use sealant 1052366 or cover gasket
only.
Install cover and torque cover bolts to 27
N-m (20 1b.ft.).
12. Fill rear axle to proper level with the specified
lubricant. Refer to specifications.
LIMITED SLIP REAR AXLE (GONE TYPE)
The cone-type limited-slip differential has several
definite operating characteristics. An understanding of
these characteristics is necessary as an aid to diagnosis.
The clutch energizing force comes from the
thrust side of the gears. Consequently, a free spinning
wheel may not have enough resistance to drive torque
to apply the clutch cones. If this occurs, apply the
parking brake a few notches which will provide enough
resistance to energize the clutch cones.
Energizing the clutch cones is independent of
acceleration; therefore, a very slow application of the
throttle on starting is recommended to provide
maximum traction by preventing "break away" of
either rear wheel.
Improper operation is generally indicated by cone
slippage or grabbing. Sometimes this produces a
chatter or whirring sound. However, these sounds do
not always indicate failure as they could be produced
from a lack of proper lubrication. For example, under
certain conditions where one wheel is on
a very slippery
surface and the other on dry pavement, wheel spin can
occur if over acceleration is attempted. Continued
spinning may cause audible noise, such as a whirring
sound, due to the cones lacking sufficient lubricant.
This does not necessarily indicate failure of the unit.
During regular operation (straight ahead driving)
when both wheels rotate at equal speeds, there is an
approximately equal driving force delivered to each
wheel. When cornering, the inside wheel delivers extra
driving force causing slippage in both clutch cones.
Consequently, the operational life of the limited slip
unit is dependent upon equal rotation of both wheels
during straight ahead operation. If wheel rotation for
both rear wheels is not equal during straight ahead
operation, the limited-slip unit will constantly be
functioning as if the vehicle were cornering. This will
impose constant slippage on the clutch cones and will
eventually lead to abnormal wear on the clutch cones.
Therefore, it is important that there be no excessive
differences in the rear wheel tire sizes, air pressures, or

4B-18 REAR AXLE
tire wear patterns. One indication of this condition is
"swerving on acceleration." If swerving on
acceleration is encountered, check the rear wheels for
different tire size, air pressure, or excessively different
wear patterns, and tread depths, before proceeding into
an overhaul operation.
Checking Limited-Slip Operation
1. Place transmisison
in Park position.
2. Raise
rear of vehicle until wheels are off the
ground, remove one wheel and tire assembly.
3. Attach Adapter J 2619-1 to axle shaft flange and
install a 1/2-13 bolt into adapter as shown in Fig.
617,
4. With opposite wheel and tire assembly still on
vehicle and held firmly to prevent turning,
measure torque required to rotate opposite axle
shaft with a torque wrench attached to J 2619-1.
If the torque reading is less than 48
N.m (35 lb.
ft.) the unit should be disassembled and repaired
as required.
5. The Auburn rear axle check with both tires
elevated and transmission in park (differential
case not allowed to rotate).
The torque required to rotate one wheel should
be 169 to 305
N-m (125 to 225 1bs.ft.).
6. This is the Auburn rear axle check with only one
rear wheel raised and transmission in neutral (dif-
ferential case free to rotate). The torque required
to rotate one wheel is
60 to 136 N-m (45 to 100
lbs. ft.)
7. Reinstall wheel and tire assembly.
AUBURN CONE TYPE
This limited slip rear axle transmits torque from
the drive pinion gear to the ring gear and to the case
in the same manner as the conventional rear axle. In
addition, the limited slip rear axle incorporates the use
of cone clutches which tend to lock the axle shafts to
the case, or in effect, to each other.
As driving torque is developed at the rear wheels,
side gear separating loads are developed which load the
rear axle cones. This induced clutch torque capacity re-
sists relative motion between the side gears and the rear
axle case. Therefore, if one wheel is on slippery pave-
ment, such as ice or snow, the other wheel must develop
considerably more torque before the case assembly will
differentiate and allow wheel spin.
The axle shaft torques developed when turning a
corner will overcome the clutch capacities and allow
differentiation.
All rear axle parts of vehicles equipped with this
limited slip rear axle are interchangeable with those
equipped with the conventional rear axle, except for
the case assembly. It is similar in all respects to the
conventional case assembly, with the addition of cone
clutches splined to each side gear.
INOWERVICEABLE) PINION SHAFT SCREW
Figure 6 16 Auburn Cone Type Case
Remove or Disconnect
Figure 6 16
This limited slip rear axle case is non-serviceable,
1. Follow the procedures under standard case
removal in this section.
2. Case side bearings using Tool J-22888.
3. All ring bolts except for two opposite ones.
4. Loosen the two remaining bolts slightly.
5. Tap on the two bolts alternately to loosen ring
gear.
Install or Connect
1.
Ring gear on new case.
NOTICE: Install new ring gear bolts. Never reuse
old bolts.
2. Case side bearings on new case.
3. New case starting with the Side Bearing Preload
Adjustment procedures in this section.
1 -AXLE SHAFT PULLER J-21579
2
-ADAPTER J-2619-1
3-TORQUE WRENCH
Fig.
617 Measuring Limited Slip Rotating Torque

REAR AXLE 48-19
RING NON US US GEAR WPQ RATIO BRAKES AXLE AXLE SIZE CODE CODE
GU2 2.73 ALUMINUM DRUM
6HE
GU2 2.73 CAST IRON DRUM 6HP
GU2 2.73 CAST IRON DRUM
6HT
7.625 G U4 3.08 CAST IRON DRUM 6HF
GU4 3.08 CAST IRON DRUM 6HK
G U4 3.08 ALUMINUM DRUM 6HB
GU6 3.42 CAST IRON DRUM 6HL
REAR AXLE SPEClFICAnONS
TIGHTENING SPECIFICATIONS
Bolt - Rear
Universal Joint to Pinion Flange
Strap or U-Bolt
- All ................................................................................ 20 Nem (15 LBS. FT.)
Bolt
- Rear Axle Housing Cover to Carrier ........................................... 41 N.m (30 LBS. FT.)
Nut
- Brake Assembly to Rear Axle Housing .......................................... 48 N-m (35 LBS. FT.)
Bolt
- Ring Gear to Differential Tail Case ............................................. 120 N.m (90 LBS. FT.)
Bolt
- Bearing Cap to Carrier ....................................................................... 81 N-m (60 LBS. FT.)
Nut
- Rear Wheel to Axle Shaft .................................................................. 108 N-m (80 LBS. FT.)
Nut
- Filler Plug ............................................................................................. 34 N-m (26 LBS. FT.)
LlMlTS FOR FI"TTINGS AND
ADJUSTMENTS
Pinion Bearing Pre-Load (Measured at Pinion Flange Nut)
New Bearings
................................................... 2.26 - 2.82 N-m (20-25 LBS. IN.) Rotating Torque
............................................. Reused Bearings - All 1.69 N-m (10-
15 LBS. IN.) Rotating Torque
Total Assembly Preload (Measured at Pinion Flange Nut)
New Bearings
.......................................... 3.95 - 4.52 N.m (35-40 LBS. IN.) Rotating Torque
.......................................... Reused Bearings 2.26 - 2.82 N.m (20-25 LBS. IN.)
Rotating Torque
Ring Gear Position
........................................................................................ .006"-.008" Backlash
Fig. 618 Axle Usage Chart

dB-20 RWR AXLE
1. J 29609 REAR PINION BEARING INSTALLER 18. J 21022-02
FRONT PINION BEARING REMOVER
2.
J 2619-01 SLIDE HAMMER ASSEMBLY 19. J 21579-12 AXLE
SHAFT PULLER
3.
J 2619-1 ADAPTER 20. J 21777-40 PINION
SETING GAGE PILOT
I 4.J2619-4SLlDEHAMMERADAPTER 21. J 21777-42 FRONT PINION BEARING PILOT
5. J 6133-01 FRONT PINION BEARING INSTALLER 22. J 21777-43
PINION SETTING GAGE
6. J 6197-A PINION BEARING RACE INSTALLER 23. J 22536
PINION DRIVER
7.
J 6407-1 PRESS PLATE HOLDER 24. J 22813-01 AXLE
SHAFT BEARING AND SEAL
8.
J 25588 SlDE BEARING SHIM INSTALLER REMOVER
9.
J 6627-A WHEEL STUD REMOVER 25. J 228888
CASE SlDE BEARING PULLER
10.
J 7057 DlAL INDICATOR PLUNGER EXTENSION 26. J 23597-1 BODY
PlNlON SETTING GAGE
11.
J 7817 FRONT PlNlON BEARING RACE INSTALLER 27. J 23597-1-6
BODY PlNlON SETING GAGE
12.
J 8001 DlAL INDICATOR ASSEMBLY 28. J 23597-11
PlNlON SETING GAGE
13.
J 8092 DRIVER HANDLE 29. J 23597-12
REAR SETTING GAGE
14.
J 8107-2 SlDE BEARING PULLER ADAPTER 30. J 23765 AXLE SHAFT BEARING
INSTALLER
15.
J 8614-01 PINION FLANGE REMOVER AND INSTALLER 31. 23771 AXLE SHAFT SEAL INSTALLER
16.
J 21777-45 PlNlON SETTING GAGE SHAFT 32. J 2391
1 PlNlON OIL SEAL INSTALLER
DISCS (2 REQUIRED) 33. J 33868
REAR PINION BEARING REMOVER
17.
J 22912-01 REAR PINION BEARING REMOVER 34. J 25299 SIDE BEARING
INSTALLER ~10007-40-F
Fig. 619 Special Tools

BRAKES
NOTICE: All brake attaching fasteners are important attaching parts in that they could affect the performance of vital parts
and systems.
andlor could result in major repair expense . They must be replaced with one of the same part number or with an
equivalent part if replacement becomes necessary
. Do not use a replacement part of lesser quality or substitute design .
Torque values must be used as specified during reassembly to assure proper retention of parts .
CAUTION: When servicing brake parts. do not create dust by grinding. sanding brake linings. or by cleaning brake
parts with a dry brush or with compressed air
. Many brake parts contain asbestos fibers which can become airborne if
dust is created during servicing
. Breathing dust containing asbestos fibers may cause serious bodily harm . A water
dampened cloth or water based solution should be used to remove any dust on brake parts
. Equipment is commer-
cially available to perform this washing function
. These wet methods will prevent asbestos fibers from becoming
airborne
.
CONTENTS
......................... General Description 5.2
Composite Master Cylinder
.................. 5.2
Brake Fluid Level
lndicatgr ................... 5.2
Operation of Disc Brake
..................... 5.2
Operation of Drum Brake
.................... 5.2
Operation of Combination Valve
............... 5.2
Brake Pressure Differential
.......................... Warning Switch 5.2
Diagnosis and Inspection ..................... 5.3
Brake System Testing
....................... 5.3
External Conditions That Affect Brake Performance
.................... -5-3
Warning Lamp Operation .................... 5.3
Brake Fluid Leaks
.......................... 5.3
Master Cylinder Check
...................... 5.3
Substandard or Contaminated
BrakeFluid ............................. 5-3
............................. On-Car Service 5.7
Brake Pedal Replacement
................... 5.7
Stoplamp Switch Adjustment ................. 5-7
Filling Master Cylinder Reservoirs
............. 5-7
Bleeding Brake Hydraulic System
............. 5.7
Manual Bleeding
......................... 5.8
Pressure Bleeding
........................ 5.8
Flushing Brake Hydraulic System
............. 5.9
Brake Pipe Replacement
.................... 5.9
............................. I.S.O. Flare 5.9
Brake Hose Inspection
...................... 5.9
Brake Hose Replacement
.................... 5.11
Front Brake Hose
........................ 5.11
....................... Center Brake Hose 5.12
..................... Rear Disc Brake Hose 5.12
ParkingBrake ............................. 5-13
Parking Brake Control Assembly
.............. 5.13 Parking Brake Cables
....................... 5.14
Parking Brake Front Cable
................. 5.14
Parking Brake Rear Cable (Drum Brakes)
..... 5.14
Parking Brake Rear Cable (Disc Brakes)
...... 5.15
Brake Lining Inspection
..................... 5.15
............. Inspecting and Refinishing Rotors 5-15
Thickness
Variat~on Check ................. 5.15
Lateral
Runout Check ..................... 5.15
Rotor Tolerance and Surface Finish
.......... 5.16
Refinishing Brake Rotors
.................. 5-16
lnspecting and Refinishing Brake
Drums
................................. 5-16
Cracked Scored, or Grooved Drum
.......... 5.16
Out-of-Round or Tapered Drum
............. 5.16
Refinishing Brake Drums
.................. 5.16
Brake Drum Balance
..................... -5-16
Combination Valve ......................... 5.17
Testing Combination Valve Electrical
............................... Circuit 5.17
Testing Combination Valve Warning
.......................... Lamp Switch 5.17
.......... Combination Valve Replacement 5.17
............ Power Brake Vacuum Hose Filter 5.17
Unit Repair
................ Composite Master Cylinder .5A 3.1
Disc Brake Caliper Assembly
....................... 300013100 Series 581 -1
Disc Brake Caliper Assembly
3548 Series
........................... .5B 6.1
........ Direct Torque Drum Brake Assembly .5C 3.1
Power Head Assembly
-
.................... Tandem Diaphragm .5D 2.1
.............. Specifications and Special Tools 5F-1

5-2 BRAKES
GENERAL DESCRIPTION
COMPOSIE EASTER CYLINDER
This vehicle uses a composite master cylinder which has
an aluminum body and a clear nylon reservoir with fluid
level indicators. The master cylinder uses a "quick take-up" feature in the
rear chamber to reduce pedal travel which may result from
increased fluid displacement required to move the caliper
piston. The quick take-up master cylinder includes a spring
loaded ball check valve which holds pressure in the
large-
diameter rear chamber. When the brake is first applied, the
movement of the rear piston causes fluid to be displaced
forward, past the primary piston primary seal and into the
primary high pressure chamber, which feeds the front
brakes. At a predetermined pressure, 480-690
kPa (70-100
mi), the ball unseats and fluid from the largi! rear bore is
disblaced past the ball and into the reservoir. The primary
and secondary high pressure chambers supply pressure to
the front and rear brakes, respectively, in the usual way.
When the pedal is released, the large-bore chamber is filled
with fluid by drawing fluid from the reservoir around the
quick take-up lip seal, and also through a small orifice in the
ball seat.
BRAKE FLUID LEVEL INDICATOR
(Figure 1)
The nylon master cylinder reservoir has two windows
which allow the brake fluid level to be checked without
removal of the reservoir cover.
OPERATION OF DISC BRAKE
When the brakes are applied, fluid pressure behind the
caliper piston increases. Pressure is exerted equally
against the bottom of the piston and also against the bottom
of the piston bore. The pressure applied to the piston is
transmitted to the inner shoe and lining, forcing the lining
against the inner rotor surface. The pressure applied to the
bottom of the piston bore forces the caliper to slide on the
Figure
1 Master Cylinder Reservoir Window (Typical) mounting bolts toward the inner side,
or toward the car.
Since the caliper is one piece, this movement toward the
car causes the outer section of the caliper to apply pressure
against the back of the outer shoe and lining assembly,
forcing the lining against the outer rotor surface. As line
pressure increases, the shoe and lining assemblies are
pressed against the rotor surfaces with increased force,
bringing the car to a stop. When line pressure is released,
the seal and seal groove cause the piston to be slightly
retracted, resulting in less drag on the rotor by the shoe and
lining assembly.
Outward movement of the piston and inward movement
of the caliper automatically compensate for lining wear. As
the linings wear, the increased area behind the piston is
filled with brake fluid from the master cylinder reservoir.
OPERATION OF DRUM BRAKE
The drum brake assembly is a duo-servo design. In the
duo-servo brake, the force that the wheel cylinder applies to
the primary shoe is
multipled by the primary lining friction to
provide a very high force applied to the secondary shoe.
Torque from the brake shoes is transferred through the anchor pin to the axle flange. Adjustment is automatic when
the brakes are applied while the car is backing up.
OPERATION OF COMBINATION VALVE
The metering, or hold-off section of the combination
valve, limits pressure to the front disc brakes until a prede-
termined front input pressure is reached, approximating
the pressure to overcome the rear shoe and lining retractor
springs. There is no restriction at inlet pressures below 20
kPa (3 psi) to allow for pressure equalization during non
apply periods.
To prevent early rear wheel lock-up under heavy braking
loads, the proportioning section of the combination valve
proportions outlet pressure to the rear brakes after a prede-
termined rear input pressure has been reached.
The valve has a by-pass feature which insures full system
pressure to the rear brakes in the event of a front brake
system failure. Similarly, full front pressure is retained in
the event of a rear brake pressure failure.
BRAKE PRESSURE DIFFERENTIAL
WARNING
SWITCH
The pressure differential warning switch constantly com-
pares brake pressure in both parts of the system. The
switch will activate the "BRAKE" warning lamp on the
instrument panel in a failure in either part. The combination
valve is designed so the switch will stay in the "warning"
position once a failure has occurred. The lamp can only be
turned off by repairing the failure and applying a pedal force
as required to develop up to 3100
kPa (450 psi) line pres-
sure.