Pontiac FIREBIRD 1972 Service Manual page 437

SECTION 5 A
DELCO-MORAINE POWER BRAKE
SINGLE DIAPHRAGM
The following caution applies to one or more steps in the assembly proce-
dure of components in this portion of the manual as indicated at appropri-
ate locations by the terminology "See Caution on page 1 of this Section".
CAUTION: THIS FASTENER IS A N IMPORTANT A TTACHING
PART IN THAT IT COULD AFFECT THE PERFORMANCE OF
VITAL COMPONENTS AND SYSTEMS, AND/OR COULD RE-
SULT IN MAJOR REPAIR EXPENSE. IT MUST BE REPLACED
WITH ONE OF THE SAME PART NUMBER OR WITH AN
EQUIVALENT PART IF REPLACEMENT BECOMES NECES-
SAR X DO NOT USE A REPLACEMENTPAR T OFLESSER QUAL-
ITY OR SUBSTITUTE DESIGN TORQUE VALUES MUST BE
USED AS SPECIFIED DURING REASSEMBLY TO ASSURE
PROPER RETENTION OF THIS PAR i ?
CONTENTS OF THIS SECTION
Trouble Diagnosis and Testing
..............................
5A-1
Minor Repairs
..........................................................
5A-5
System Tests
......................................................
5A-1
Overhaul Power Unit
..............................................
5A-6
Trouble Diagnosis
................................................
5A-1
Master Cylinder-Remove
......................................
5A-5
General Description
................................................
5A-2
Front Housing-Remove
..........................................
5A-5
Design
......................................................................
5A-3
Power Piston-Disassemble
......................................
5A-6
Principles of Operation
........................................
5A-3 Power Piston-Install
..............................................
5A-10
Vacuum Failure
......................................................
5A-4
Front Housing-Replace
........................................
5A- 10
........................................
Checks and Adjustments 5A-4
TROUBLE DIAGNOSIS AND TESTING
SYSTEM TESTS
Road test the brakes by making a brake application at
about 40 mph to determine if the vehicle stops evenly and
quickly. If the pedal has a spongy feel when applying the
brakes, air may be present in the hydraulic system and
bleeding of brakes may be required.
When the engine is stopped and the transmission is in
neutral, apply brakes several times to deplete all vacuum,
reserve in the system. Depress brake pedal, hold light-foot
pressure on the pedal, and start the engine. If the vacuum
system is operating, the pedal will tend to fall away under
foot pressure, and less pressure will be required to hold
pedal in applied position. If no action is felt, the vacuum
system is not functioning.
Stop engine and deplete all vacuum reserve in the system.
Depress the brake pedal and hold foot pressure on the
pedal. If the pedal gradually falls away under foot pres-
sure, the hydraulic system is leaking.
If the brake pedal travels to within one inch of the toe-
board, the brake shoes require adjustment or relining.
Start engine with brakes off, run to medium speed and
turn off the ignition. Immediately close the throttle to
build up vacuum. Wait at least 90 seconds, then try brake
action. If not vacuum assisted for two or more applica-
tions, vacuum check valve is faulty or leak exists in
vacuum system.