Pontiac Fiero 1988 Service Manual page 225

5-4 BRAKES
B R A K E DIAGNOSIS CHART —
POWER B R A K E UNIT T R O U B L E DIAGNOSIS
The same types of brake troubles are encountered with power brakes as with standard brakes. Before checking
power brake system for source of trouble, see "BRAKE DIAGNOSIS CHART — 4 WHEEL DISC SYSTEMS." After
these possible causes have been eliminated, check for cause as outlined below;
HARD PEDAL
CAUSE CORRECTION
Broken or damaged hydraulic brake lines.
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.
CRABBY B R A K E S
(Apparent Off-On Condition)
CAUSE CORRECTION
Broken or damaged hydraulic brake lines. 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 at disc brake calipers or in pipes or connections. Inspect and repair as necessary.
Air in hydraulic system. Bleed system.
BRAKES FAIL TO RELEASE
CAUSE 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.
J10003-5-P
Figure 3 V a c u u m Booster Diagnosis (Chart)