Pontiac Fiero 1988 Service Manual page 226

BRAKES 5-5
wheels will stop 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.
C.iernal 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 the 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
permits the front wheel to tilt and have spotty contact
with the brake shoe linings causing erratic brake
operation.
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 " R U N " position.
The following conditions will activate the " B R A K E "
warning lamp:
1. Parking brake applied. The lamp should be on when
the parking brake is applied and the ignition switch is
" O N . "
2. Pressure differential switch detects a failure. See
"Brake Pressure Differential Warning Switch" in this
section.
B R A K E FLUID L E A K S
With engine running at idle and the transaxle in neutral,
depress the brake pedal and hold a constant foot pressure.
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 one inch from the top if the linings are
worn. This is not abnormal.
MASTER CYLINDER C H E C K
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.
SUBSTANDARD OR CONTAMINATED
B R A K E FLUID
Improper brake fluid, mineral oil or water in the fluid may
cause the brake fluid to boil or the rubber components to
deteriorate.
If primary piston cups are swollen, the rubber parts have
deteriorated. This deterioration may also be seen by a swol-
len master cylinder cover diaphragm.
If rubber deterioration is evident, disassemble all hydrau-
lic parts and wash with alcohol. Dry parts with compressed
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.
ON-CAR S E R V I C E
PEDAL TRAVEL
Most low pedal problems are caused by air in the hydrau-
lic system. Bleed the system until all air is purged. See
"Bleeding Brake Hydraulic System". Other less frequent
causes of excessive pedal travel are incorrect pushrod
length, improperly adjusted parking brake, linings exces-
sively worn, and hydraulic system leakage.
Measure
Tools Required:
J 28662 Brake Pedal Effort Gage
1. With engine off and key off, pump brake pedal until all
reserve is exhausted from the brake booster. (A defi-
nite change in pedal feel will occur.)