Pontiac FIREBIRD 1972 Service Manual page 440

5A-4
1972 PONTIAC SERVICE MANUAL
MASTER
CYLINDER
FRONT
HOUSINGXEAL
\
ASSEMBLY
BEARING
USH ROD
BOOT
Fig. 5A-2 Exploded View
A,
G, F and
X
Series Power Brake Unit
VACUUM FAILURE
CHECKS AND ADJUSTMENTS ON CAR
In case of vacuum source interruption, as the pedal is
pushed down, the end of the air valve contacts the reaction
levers and forces them, in turn, against the hydraulic reac-
tion plate. Since the hydraulic reaction plate is fastened to
the vacuum cylinder push rod, it forces the rod against the
master cylinder pistons, which build up the hydraulic line
pressure.
The pedal pressure required for a manual application,
such as described, is considerably greater than with
vacuum assist.
1. Check for free operation of brake pedal. If binding
exists, check pivot points for binding and lubricate as
required.
2. Check stop light switch for proper setting and operat-
ion.
3. Check fluid level in hydraulic cylinder reservoirs.
Fluid level should be as shown in Fig. 5-1 1.
4. Check vacuum hose, check valve grommet and car-
buretor vacuum fitting for possible air leaks.
5. Check engine for good stall-free idle. Correct as re-
quired.