1988 PONTIAC FIERO Service Repair Manual

5-4 BRAKES
Figure 2 Brake System Diagnosis

BRAKES 5-5
BRAKE DIAGNOSIS CHART - 4 WHEEL DISC SYSEEMS
XX - Indicates more probable cause(s) 'May be a normal condition.
X - Indicates other
Figure 3 4-Wheel Disc Brake Diagnosis

HARD PEDAL
CORRECTION
Broken or damaged hydraulic brake pipes. Inspect and replace
as necessary.
Vacuum failure. Check for:
Faulty vacuum check valve or grommet. Replace.
Collapsed or damaged vacuum hose. Replace.
Plugged or loose vacuum fitting. Repair.
Faulty air valve seal or support plate seal. Replace.
Damaged floating control valve. Replace.
Bad stud welds on front or rear housing or power head.
Replace unless easily repaired.
Faulty diaphragm. Replace.
Restricted air filter element. Replace.
Worn or distorted reaction plate or levers. Replace
plate or levers.
Cracked or broken power pistons or retainer. Replace power pistons and piston
rod retainer.
GRABBV BRAKES
(Apparent Off-On Condition)
CORRECTION
Broken or damaged hydraulic brake pipes. Inspect and replace
as necessary.
Insufficient fluid in master cylinder. Fill
reservoirs with approved brake fluid. Check for
leaks.
Faulty master cylinder seals. Repair or replace
as necessary.
Cracked master cylinder casting. Replace.
Leaks in pipes or connections at disc brake calipers or Inspect and repair
as necessary.
Air in hydraulic system. Bleed system.
BRAKES
FAIL TO RELEASE CORRECTION
Blocked passage in power piston. Inspect and repair or replace
as necessary.
Air valve sticking shut. Check
for proper lubrication of air valve
"0" ring.
Broken piston return spring. Replace.
Broken air valve spring. Replace.
Tight pedal linkage. Repair or replace
as necessary.
Figure
4 Vacuum Booster Diagnosis

BRAKES 5-7
ONmCAR SERVICE
BRAKE PEDAL REPLACEMENT
See Figure 5.
STOPLAMP SWITCH ADJUSTMENT
Adjust (Figure 6)
With brake pedal in fully released position, the stop-
lamp switch plunger should be fully depressed
against the brake pedal shank. Adjust switch by mov-
ing in or out as necessary.
1. Make certain that the tubular clip is in brake pedal
mounting bracket.
2. With brake pedal depressed, insert switch into tubu-
lar clip until switch body seats on clip. Clicks can be
heard as the threaded portion of the switch is pushed
through the clip toward the brake pedal.
3. Pull brake pedal fully rearward against brake pedal
stop until clicking sounds can no longer be heard.
Switch will be moved in tubular clip providing adjust-
ment.
4. Release brake pedal and then repeat step 3, to
assure that no clicking sounds remain.
FILLING MASTER CYLINDER RESERVOIRS
The master cylinder must be kept properly filled to insure
adequate reserve and to prevent air from entering the hydraulic
system. However, because of expansion due to
heat absorbed from brakes and from engine, master cylin-
der must not be overfilled.
The brake fluid reservoir is on the master cylinder which
is located under the hood on the left side of the vehicle.
Thoroughly clean reservoir cover before removal to avoid
getting dirt into reservoir. Remove cover and diaphragm.
NOTICE: Do not use fluid which contains a petro-
leum base. Do not use a container which has been
used for petroleum based fluids or a container which
is wet with water. Petroleum based fluids will cause
swelling and distortion of rubber parts in the hydrau-
lic brake system and water will mix with brake fluid,
lowering the fluid boiling point. Keep all fluid con-
tainers capped to prevent contamination.
Add fluid as required to bring level to
approximately6mm
(114-inch) from top of reservoir. Use Delco Supreme No. 1 1
Hydraulic Brake Fluid or equivalent. Fluid must be "DOT
3."
BLEEDING BRAKE HYDRAULIC SYSTEM
A bleeding operation is necessary to remove air when it is
introduced into the hydraulic system. It may be necessary to bleed the hydraulic system at all
four brakes if air has been introduced through a low fluid
level or by disconnecting brake pipes at master cylinder. If a
Figure
5 Brake Pedal Mounting

5-8 BRAKES
1 -PEDAL 4-SWITCH
(WITH CRUISE CONTROL)
2- RETAINER
5-PEDAL SUPPORT
3-SWITCH
I lWlO CRUISE CONTROLl J10003-5-F
Figure 6 Stoplamp Switch Adjustment
brake pipe is disconnected at one wheel, only that wheel
cylinderlcaliper needs to be bled. If pipes are disconnected
at any fitting located between master cylinder and brakes,
then the brake system served by the disconnected pipe
must be bled.
Manual Bleeding (Figure
7)
Tools Required:
J 21472 Bleeder Wrench
J 28434 Rear Wheel Cylinder Bleeder Wrench
The time required to bleed the hydraulic system can
be reduced if the master cylinder is filled with fluid and
as much air as possible is expelled before the cylinder is
installed on the vehicle.
Power brakes require removing the vacuum reserve by
applying the brakes several times with the engine off. Care
must be taken to prevent brake fluid from contacting any
painted surface.
1. Fill the master cylinder reservoirs with brake fluid and
keep at least half full of fluid during the bleeding oper-
ation.
2.
If the master cylinder is known or suspected to have
air in the bore, then it must be bled before any wheel
cylinder or caliper in the following manner:
a. Disconnect the forward (blind end) brake pipe
connection at the master cylinder.
b. Allow brake fluid to fill the master cylinder bore
until it begins to flow from the forward pipe con-
nector port.
c. Connect the forward brake pipe to the master
cylinder and tighten. d.
Depress the brake pedal slowly one time and
hold. Loosen the forward brake pipe connec-
tion at the master cylinder to purge air from the
bore. Tighten the connection and then release
the brake pedal slowly. Wait
15 seconds.
Repeat the sequence, including the
15 second
wait, until all air is removed from the bore.
e. After all air has been removed at the forward
connection, repeat step d and bleed the master
cylinder at the rear (cowl) connection.
f. If it is known that the calipers and wheel cylin-
ders do not
coiitain any air, then it will not be
necessary to bleed them.
Individual wheel cylinders or calipers are bled only
after all air is removed from master cylinder.
a. Place a proper size box end wrench or
J 21 472
over the bleeder valve. Rear wheel cylinder
bleeder screws require tool
J 28434. Attach a
clear tube over bleeder valve and allow tube to
hang submerged in a clear container partially
filled with brake fluid. Depress the brake pedal
slowly one time and hold. Loosen the bleeder
valve to purge the air from the cylinder. Tighten
bleeder screw and slowly release pedal. Wait
15 seconds. Repeat the sequence, including
the 15 second wait until all air is removed. It may
be necessary to repeat the sequence ten or
more times to remove all the air. Rapid pumping
of the brake pedal pushes the master cylinder
secondary piston down the bore in a way that
makes it difficult to bleed the rear side of the
system.
If it is necessary to bleed all of the calipers or wheel
cylinders, the following conventional sequence
should be followed: a. right rear
b. left rear
c. right front
d. left front
Check the brake pedal for "sponginess" and the
"BRAKE" warning lamp for indication of unbalanced
pressure. Repeat entire bleeding procedure to cor-
rect either of these two conditions.
Pressure Bleeding (Figures
7 and 8)
Tools Required:
J 21472 Bleeder Wrench
J 28434 Rear Wheel Cylinder Bleeder Wrench
J 29532 Bleeder
J 29567 Bleeder Adapter
J 35856 Proportioning Valve Depressor
NOTICE: Pressure bleeding equipment must be
the diaphragm type and must have a rubber dia-
phragm between the air supply and the brake fluid to
prevent air, moisture, oil and other contaminants
fram entering the hydraulic system. It is very impor-
tant that the correct master cylinder bleeder adapter
be used to avoid possible damage to the master
cylinder reservoir.
1. Install J 29567 to the master cylinder reservoir.
2. Make sure the pressure tank is at least
lh full of Delco
Supreme $1 1 brake fluid or equivalent. The bleeder
must be bled each time fluid is added.

BRAKES 5-9
TUBE hlUST BE
SUBMERGED IN
Figure 7 Bleeding Brakes
3. Charge the bleeder to 140-172
kPa (20-25 psi).
4. Connect line to adapter. Open the line valve and
depress bleed off valve on top of adapter until a few
drops of fluid appear.
5. Rear drum brakes require manual override of the
combination valve to permit flow to the front wheels. Use
J 35856 to hold the valve stem open when pres-
sure bleeding.
6. Raise car. See Section
OA.
7. Bleed the brakes in the following sequence:
a. right rear
b. left rear
c. right front
d. left front
8. Place a proper size box end wrench or
J 21472 over
the bleeder valve. Attach a clear tube over valve and
allow tube to hang submerged in a clear container
partially filled with brake fluid. When bleeding drum
brakes, use
J 28434 on the bleeder screw. Attach the
bleeder tubing to the tool and submerge the other end
in a clean container partially filled with brake fluid.
9. Open the bleeder valves at least 3/4 turn and allow
flow to continue until no air is seen in the fluid.
10. Close the bleeder valves or screws.
Be sure they seal.
11. Repeat steps
7 through 10 until all calipers and wheel
cylinders have been bled.
12. Lower car. See Section OA.
13. Check the brake pedal for "sponginess" and the
"BRAKE" warning lamp for indication of unbalanced
pressure.
* Repeat entire bleeding procedure to correct
either of these two conditions.
14. Remove brake bleeding equipment from master cyl-
inder.
FLUSHING BRAKE HYDRAULIC SYSTEM
It is recommended that the complete hydraulic system be
thoroughly flushed with clean brake fluid whenever new
parts are installed in the hydraulic system.
1 - MASTER CYLINDER
u 2 - HOSE TO BLEEDER
Figure 8 Pressure Bleeding Adapter (Typical)
The system must be flushed if there is any doubt about
the grade of fluid in the system or if fluid has been used
which contains the slightest trace of mineral oil.
All rubber parts that have been used with contaminated
fluid must be replaced.
BRAKE PIPE REPLACEMENT
(Figures
9 through 11)
Tool Required:
J 29803 I.S.O. Flaring Tool
CAUTION: Never use copper tubing because
copper is subject to fatigue cracking and corro-
sion which could result in brake failure. Use dou-
ble-walled steel tubing.
I.S.O. Flare
1. Obtain the recommended tubing and steel fitting nuts
of the correct size. Outside diameter of tubing is used
to specify size.
2. Cut tubing to length. Correct length may be deter-
mined by measuring old pipe using a string and
adding 3mm ('la-inch) for each I.S.O. flare.
3. Make sure fittings are installed before starting flare.
Flare tubing ends using I.S.O. flaring kit
J 29803. Fol-
low instructions included in tool set.
4. Bend pipe assembly to match old pipe using a tubing
bender. Clearance of
19mm (314-inch) from all moving
parts and
13mm (lh-inch)from all vibrating parts must
be maintained.
BRAKE HOSE INSPECTION
0 inspect
The flexible hydraulic brake hoses, which transmit
hydraulic pressure from the steel brake lines on the body to
the rear axle and the calipers, should be inspected at least
twice a year when the car is on a lift for lubrication. The

5-10 BRAKES
-
Figure 9 Front Brake Hoses and Pipes (Typical)

BRAKES 5-11
Figure 10 Center Brake Pipes (Typical)
brake hoses should be checked for road hazard damage,
for cracks and chafing of the outer cover and for leaks and
blisters.
A light and mirror may be needed for an adequate
inspection.
If any of the above conditions are observed on a
brake hose it will be necessary to replace it.
Do not allow brake components to hang from the flexible
hoses as damage to the hoses may occur. Some brake
hoses have protective rings or covers to prevent direct con-
tact of the hose with other chassis parts. Besides causing
possible structural damage to the hose, excessive tension
could cause the hose rings to move out of their proper
locations.
BRAKE HOSE REPLACEMENT
Front Brake Hose (Figure 9)
Remove or Disconnect
1. Wheel and tire. See Section 3E.
Clean
* Dirt and foreign material from hoses and fit-
tings.
2. Brake pipe from hose. 0 Use a backup wrench on hose fitting.
* Be careful not to bend bracket or pipe.
3. Spring clip from female fitting at bracket.
4. Hose from bracket.
5. Bolt, hose, and two copper gaskets from caliper.
* Discard two copper gaskets.
Install or Connect (Figure 9)
NOTICE: See "Notice" on page 5-1 for steps 1
and 3.
1. Bolt, hose, and two copper gaskets to caliper.
0 Use new copper gaskets.
Lubricate bolt threads with brake fluid.
0 Fitting flange must engage caliper orientation
ledge.
Tighten
0 Bolt to 44 N.m (32 Ibs. ft.).
2. Hose into bracket.
There should be no kinks in hose.
3. Spring clip at hose mounting bracket.
4. Brake pipe to hose. 0 Use backup wrench on hose fitting.
0 Make sure that hose does not make contact
with any part of suspension. Check in extreme
right and extreme left turn conditions.
* Fittings to 15 N.m (1 1 Ibs. ft.).
5. Bleed brake system. See "Bleeding Brake Hydraulic
System" in this section.