1988 PONTIAC FIERO Service Repair Manual

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 4B1-13
1-DIFF. CASE
2-SIDE GEAR
(2)
3-THRUST WASHER (S. G.) (2)
4-DIFF. CASE
5-PINION CROSS
SHAFT
(1)
6-RETAINER PINS (3)
7-PINION SHAFT
(SHORT) (2)
8-THRUST WASHERS (DIFF PINION) (4)
9-DIFF. PINIONS (4)
10-THRUST BLOCK
(1) I
11-SIDE CASE
BEARINGS
I 52001 3-481
Fig. 14 Standard Differential Assembly
6. Differential case.
lmportant
a. Check
the casting for general soundness.
b. If
the bearings are removed, journals must
be free from tears as damaged journals
result in premature bearing failures. The
bearing abutment faces on the housing must
be free from dirt and burrs. The ring gear
pilot and mounting face should be clean and
free from tears and burrs.
c. The
mating surfaces of the two housing
halves should be clean and free from burrs.
d. The
thrust surfaces for the side gears and
pinions should be examined for excessive
wear.
e. The
side gear journal bores should be clean
and free from scores.
f. The cross shaft bores should not be oval.
7. Carrier
lmportant
a. Check
the castings all over for general
soundness. All bearing bores and abutment
faces must be clean and free from burrs.
b. Examine
oil passages and ensure they are
free from burrs.
c. Bore for
pinion seal should be free from
tears.
d. Rear
cover face and bolt holes should be
checked for damage.

4B1-14 REAR AXLE
8. Shims should be clean and free from burrs.
9. Check rear cover for tears and any damage which
may prevent effective sealing.
10. Discard all damaged bolts.
Assemble
Differential Assembly
Lubricate all gears and thrust washers with rear
axle lubricant.
Install side gears thrust washers in differential
case. Hold washers in place with grease.
Install side gear in differential case large half.
Position thrust block in case.
Drive long pinion cross shaft through case,
thrust washers, pinion, and thrust block bores.
Align retainer pin hole with hole in
case.Caution
should be taken so differential pinion thrust
washers are not damaged.
Install other two pinions and thrust washers in
differential case large half. Drive two short pinion
cross shafts through case, pinions and into thrust
block bores. Align retainer pin holes with holes
in case.
Drive three cross shaft retaining pins through
case and shafts. Leave the long cross shaft
retaining pin protruding 6 mm from case locating
other case half.
Install remaining side gear and thrust washer in
small case half.
Install side gear through case bore, and mate the
case halves on retaining pin. Rotate side gear to
ensure that gears are meshing.
Install ring gear on housing and tighten bolts to
the specified torque.
Flanged head durlok bolts can be re-used after
cleaning.
Important
NOTICE: Left hand thread bolts.
11. Press differential bearings on housing journals
with tool
5-2 1784. (Fig. 16).
Assemble
Differential Bearing Preload Spacer Selection
CAUTION: Po adjust differential side
bearing preload, change the thickness
of the right and left shims equally,
thus leaving the original backlash
undisturbed.
1. Before installation of case assembly, make sure
side bearing surfaces are clean and free of burrs.
Lubricate side bearings with gear lube. If reusing
original bearings, the original outer races must
also be used.
2. Place differential case, with bearing outer races in
position, in carrier.
Fig. 16 Differential Bearing Installation
NOTICE: As a safety precaution, install the left
bearing cap loosely so that the case may be moved
while checking adjustments bolt can be added as
an extra safety precaution in the lower right
bearing cap hole. This will prevent the case from
dropping
while making shim adjustments.
3. Achieve a slip fit between the carrier and the side
bearings as follows:
NOTICE: A slip fit means zero pre-load, or the
point at which bearings have no play and no drag.
At this point, in and out movement of the case is
possible, but side to side movement is not.
a. Measure production spacers, and subtract
.004" from each reading. Do not mix the left
and the right spacers.
b. Use
a service spacer for each side equal to
the thickness of the original shim minus
.004" and install as shown in Fig. 16 (flat
edge of spacer against housing). This will
duplicate the original setting minus
pre-load.
c. If this does not provide the proper slip fit,
shims must be added or removed equally
from both sides as necessary.
d. Check case for zero end play, lateral
motion, with dial indicator.
CAUTION: If insertion of shims
causes excessive pinion to ring gear
contact (noticeable difficulty in
rotation of the case), select thinner

REAR AXLE 481-1 5
Fig. 17 Installing Service Shims
left shim and add difference to the
right side. Keep total shim thickness
at a value equal to that obtained in
step b.
NOTICE: Original light drag is caused by weight
of the case against the carrier while additional drag
is caused by side bearing preload.
For convenience in setting backlash and tooth
contact, the preload will not be added until the
final step.
4. Check backlash and tooth pattern as described in
the following section. The bearing caps must be
installed and the bolts torqued to specified torque
(follow assembly sequence below).
5. When backlash and tooth pattern operations are
complete, remove shim packs taking care not to
mix them. Select new shims for each side
.004"
thicker than those removed and install each shim
on its proper side. This additional thickness will
provide proper bearing preload. It will be
necessary to tap the
final shim into place with a
soft hammer and tool
5-25588 (Fig. 17).
1. FRONT PINION
BEARING AND
RACE
2. SPACER
J 351 18-5
3.
SIDE DISCS J 21 777-45
4. THRU BOLT J 21 777-43 5.
SPACER
J 21777-42
6. REAR PINION
BEARING
7. ARBOR
J 23597-1
8. GAGE PLATE
351 18-2
J10003-4B1 -F
Fig. 18 Hypoid Pinion and Bearing Shim Selection
1. Drive front pinion bearing cup in the carrier
(Item a) with tool
5-7817. (Fig. 19).
1-J-8092 DRIVE
NOTICE: Check total rotational torque. Total
torque with differential case preloaded and pinion Fig. 19 Front Pinion Bearing Cup Installation
installed should be 4 to 6 in. lb, over pinion bearing
preload specification. If total rotational torque 2. Fit spacer (item
b) into carrier bore.
does
not- meet this specification, reset the
differential bearing preload spacers as developed in 3. Slide the rear pinion bearing and cap (item f) onto
steps
3 thru 5. the
thru bolt (item d) and rear bearing into axle
housing.
Assemble 4. Install thru bolt (item d) and rear bearing and cap
(item
f) into axle housing.
5. Assemble front bearing cone (item a) and spacer
(item e) onto thru bolt.
Pinion 6. Rotate nut and shaft and increase torque on the Hypoid Pinion and Bearing Shim Selection
nut until a rotational toraue of 1.7 to 2.8 N-m
(15-22 lb. in.) is obtained: Rotate the thru bolt
NOTICE: Select pinion head positioning shim using back
and forth during tightening to ensure
pattern setting kit
J 35118-A. Refer to Fig. 18. correct
seating of bearing.

4B1-16 REAR AXLE
7. Install discs on thru bolt assembly as shown in 10. After the zero setting is obtained, rotate gauge shaft
Fig.
18 and position in the carrier so that the dial
until shaft does not contact gauge plate. The dial
indicator contact rod is directly over the gauging
indicator will read the pinion depth directly.
area of the gauge plate. The discs must be fully
11.
Select correct pinion shim to be used during
seated in the side bearing bores.
pinion reassembly on the following basis. Shims
are available in increments of
(.002").
a.
If reusing production pinion, and pinion is 8. Install bearing caps over gauge shaft discs and
marked "+" (plus), correct shim will have
torque to specs.
a thickness equal to gauge reading minus
the amount specified on
ini ion.
Position gauge shaft so that the dial indicator rod
contacts the gauging area of J-35 1 18-2. Rock
gauge shaft slowly back and forth until the dial
indicator records the greatest deflection, (the
point where dial indicator needle changes
rotational direction) at the point of largest
deflection, set dial indicator to zero (Fig. 18).
Repeat rocking action of gauge shaft to verify the
zero setting. b. If production-pinion is marked "-" (minus),
correct shim will have a thickness equal to
gauge reading, plus the amount specified on
pinion.
c. If using production or service pinion which
has no marking, the correct shim will have
a thickness equal to the gauge reading.
The reading obtained from the dial indicator is
the shim size to be selected if the figure branded
on the
hypoid pinion is "0".
Pinion Branding Shim Thickness Required
-4
Add ,004" to shim selected in (12).
- 3 Add ,003" to shim selected in (12).
-2 Add .002" to shim selected in (12).
- 1 Add ,001" to shim selected in (12).
+ 1 Subtract .001" from shim selected in (12).
+2 Subtract .002" from shim selected in (12).
+3 Subtract ,003" from selected in (12).
+4 Subtract ,004" from shim selected in (12).
13. Install pinion in rear axle.
Important
a. Place the pinion selective shim into the
carrier and press the rear pinion bearing cup
into carrier with
tool 3-5590 (Fig. 30).
b. Press rear pinion bearing onto pinion with
tool
5-6133-01. (Fig. 21).
Fig. 21 Pressing Rear Pinion Bearing
c. Place pinion in carrier.
Fig. 20 Rear Pinion Bearing Cup Installation
d. Assemble the collapsible spacer and front
bearing onto pinion while supporting pinion
under head.

REAR AXLE 4B1-17
e. Assemble oiled oil seal, companion
flange, and new nut on pinion and tighten
nut to specified rotational torque while
rotating pinion forwards to seat bearing
correctly.
Important
NOTICE: If after tightening pinion nut, the
preload is excessive then the collapsible spacer
must be replaced and procedure (d) and (e)
repeated.
OPERATION OF LIMITED SLIP REAR AXLE
(CONE TYPE)
The cone-type limited-slip differential has several
definite operating characteristics. An understanding of
these characteristics is necessary as an aid to diagnosis.
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
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 Function
1. Place transmisison in Park position.
2. Raise rear of vehicle until one wheel is 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. 23.
1 -AXLE SHAFT PULLER J-21579
3-TORQUE WRENCH
Fig.
23 Measuring Limited-Slip Rotating Torque
- - 1-DIFF. CASE-FLANGE HALF 5-SHIMS (SIDE GEAR) 9-PINION SHAFT
(IF REQUIRED)
2-BRAKE CONES
(2) 10-THRUST WASHERS
6-DIFF. CASE-CAP HALF (DIFF. PINION) (4)
3-SPRING PLATES (2) 7-COMPRESSION SPRINGS 11
-MOUNTING SCREWS (8) 4-SIDE GEARS (2) 8-DIFF. PINIONS (4)
Fig. 22 Limited Slip Differential

484-18 REAR AXLE
4. With transmission in park and both wheels and
tires clear of ground, (wheels will r~tate in opp-
osite directions), measure torque required to
rotateaxle shafts with a torque
wrenchattached
to J 2619-1. If the torque reading is less than
48 N.m (35 1b.ft.) the unit should be disassembled
and repaired as required.
5. Reinstall wheel and tire assembly.
Disassemble
Limited Slip Differential.
1. Remove ring gear bolts.
NOTICE: Left hand threaded ring gear bolts.
2. Tap
ring gear off differential housing with soft
face hammer.
NOTICE: Mark differential case halves with
alignment mark before disassembly because they
could be assembled
180" off from original position.
3. Remove 8 screws holding differential housing
halves together and separate halves. 4.
Remove pinion shaft, 4 differential pinions,
thrust washers side gears, side gear shims
(if
required), spring plates, and compression springs
from housing. Discard compression springs. New
springs are required for assembly.
5. Mark each cone during disassembly to ensure
that the same brake cone will be assembled with
the same case as originally assembled. If shims
are used they must be marked so that they will be
assembled in original case half.
6. If differential bearings are damaged remove with
tool J-22888-D. (Fig. 15).
Inspect
Disassemble
The inspection procedures for the positraction
differential are the same as those for the standard
rear axle except for the side gear positioning
shims. The side gear positioning shims are used
to control case size.
1. The shims should be free of cracks, nicks, or
burrs.
2. Assemble brake cones in case and measure to
determine correct shim size. Measure the
distance from case mating surface to flat surface
on brake cone when fully seated. Select shim size
from chart below.
DISASSEMBLY INSPECTION CHART
Distance Measured mm (ins) Size
Shim Required
29.51/29.34 (1.162/1/155) no shim required.
29.64/29.54 (1.167/1.163) 0.13 (.005) shim required.
29.77D9.67 (1.172/1.168) 0.25 (.010) shim required.
Assemble
Limited Slip Differential
1.
Lubricate both sides of pinion thrust washers,
pinion bores and differential pinion shafts with
specified rear axle lube before assembling.
2. Install the 4 pinions and spherical thrust washers.
3. Replace original brake cone, shim if required, and
side gear in cap half of differential case. For shim
selection, if needed, refer to Disassembly
Inspection Chart. Apply mixture of molybdenum
disulphide and specified axle oil to face of side
gear.
NOTICE: Do not 1.eplace cone or case
independently. They must be replaced as a unit
together.
4. Install spring
plate on side gear with convex side
towards flange half.
5. Assemble differential pinion shaft, pinions, and
spherical thrust washers into cap half of
differential case with pinions meshing with side
gear. 6.
Install three new concentric thrust springs
through the center of the pinion shaft spider.
7. Assemble second spring plate and springs with
cgnvex side towards springs.
8. Coat other side gear face with molybdenum
disulphide and axle lubricant and install side gear
shim if required. Install brake cone on spring
plate.
9. Install
flange half of case on top of assembly with
oil channels aligned.
10. Install
two bolts through cases
180" apart and
tighten finger tight.
11. Axle shafts are used to align the side gear and
brake cone splines. Put a clamp on one axle shaft
so 75 mm (3 inches) extends beyond clamp.
Install differential housing onto axle shaft splines,
flanged half first.
12. Install other axle shaft through cap side of
differential case and align side gear and cone
splines.
13. Install remaining
bolts and tighten to specified
torque.
14. Install
ring gear and tighten bolts to specified
torque.

REAR AXLE 481-19
15. Press differential bearings on with tool J-21784 gear
and cone splines will occur, preventing
(Fig. 16). assembly
of remaining axle shaft. If this occurred,
16. Install assembled case into carrier following the repeat
assembly steps
11 and 12.
same procedures as developed for standard
differential.
Important
17. Installation of axle bearings and axles is the same
as standard axles. CAUTION: Do not run engine with
transmission engaged and only one
rn Important rear
wheel of vehicle elevated if rear
axle is equipped with limited slip
NOTICE:
After installing the limited slip differential. The other rear wheel will
differential in the carrier housing, be sure that both drive if in contact with the ground.
axle shafts are assembled before rotating either This action can result in damage to
axle shafts. If rotation of either axle shaft occurs the equipment or injury to the
before other is in position, misalignment of the side operator.
SPECIFICATIONS
Bolt Torque
Ring Gear Bolts
................................................................................... 13 7 N-m (101 lb. ft.)
......................................................................................... Bearing Cap Bolts 52 N-m (40
lb. ft.)
Rear Cover Bolts
........................ .. ............................................................. 26 N-m (20 lb. ft.)
........................................................................................................ Breather 14 N-m (10 Ib. ft.)
Brake Backing Plate Bolts
........................................................................... 48 N-m (36 lb. ft.)
Mounting Screws
...................... .. ............................................................... 40 N-m (30 lb. ft.)
............................................................. . Screw, Brake Line Bracket to Frame 1 1 N m (8 lb. ft.)
.......................................................... ....................... Case Half Bolt Torque 38 N.m (29 lb.
ft.)
.......................... Axle Shaft Retainer Nuts .................................... .... 46 N . m Disc (35 lb. ft.)
Bearing
Loads
Side Bearings .............................................................................. 1-3 N em (New) (10-25 lbs. in.) ' 0.5-1 N-m (Used) (6-12 lbs. in.)
............................................................. Differential Bearings 1.1-2.8 N. m (~ew) (10-25 lb.
in.)
0.5-1.4
N.m (Used) (5-12 lb. in.)
............................................................................. Hypoid Pinion 1-3 N.m (New)
(12-25 lb. in.)
0.5-1
N.m (Used) (6-12 lb. in.)
End Play
....................................... Axle Shaft (New Bearing) 0.04.mm - 0.048mm (0.001 6 - 0.0019 in.)
........................................................................ (Used Bearing) 0.076mm (0.003 in.)
Run-Out Specifications
.......................................... Differential Case/Ring Gear Mating Surface 0.05
mm (0.002") max. ................................................... ........................... Ring Gear Runout ............. 0 1 (0.005 ")
Ring Gear Backlash .......................................................... O.10mm-O.19mm (0.004 to 0.007")
Lubricant
....................... ................................................... GM Part 1050010 .. 1.7 Liters (1.8 Quarts)