Pontiac FIREBIRD 1972 Service Manual page 454

SINGLE DIAPHRAGM POWER BRAKE-BENDIX 5B-7
into the two master cylinder sections and into the reser-
voirs.
The fluid reservoirs, cast integrally with the master cylin-
der, supply fluid to the space around each piston between
the primary and secondary seals through a by-pass hole in
the casting. When the brake pedal is released quickly, fluid
pressure and the two return springs force the master cylin-
der pistons to return immediately to the released position.
If hydraulic fluid from the lines cannot return as quickly
as the master cylinder piston, compensation is provided by
a flow of fluid from the space between the primary cup and
secondary seal through the holes in the piston and around
the edge of the primary cup. The excess fluid then in the
system flows back to the reservoir through the compensat-
ing port. The secondary seal on the front piston that faces
toward the rear system prevents any flow of fluid from the
rear system to the front system and the other secondary
seal facing forward on the front piston prevents any fluid
flow from the front to the rear system. The front, or
floating piston, supplies the correct fluid displacement for
the front wheel brake requirements. The rear (or primary)
piston supplies the correct fluid displacement for the rear
wheel brake requirements. The hydraulic pressure deve-
loped in both systems is equal at all times since the front,
or floating piston, is balanced between the two hydraulic
pressures. If the front system fails, the front piston and
spring bottom and then the rear piston develops hydraulic
pressure to the rear wheels. If the rear system fails, the
rear piston and spring bottom against the front piston and
then mechanically force the front piston forward to deve-
lop hydraulic pressure to the front wheels. Failure in ei-
ther system has no effect on the other system but is
immediately evident to the driver because of the addi-
tional pedal travel required to actuate the remaining half
of the dual brake system.
CHECKS AND ADJUSTMENTS ON CAR
1. Check for free operation of brake pedal. If binding
exists, check all 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, and correct as
required.
MINOR REPAIRS
BLEEDING BRAKES
Brakes should be bled in the same manner as standard
brakes. Bleed with engine off and vacuum reserve de-
pleated. See Sections 5 and 5E for brake bleeding informa-
tion.
OVERHAUL BENDIX POWER BRAKE
MASTER CYLINDER ONLY
-
REMOVE
Certain repair operations, such as replacement of master
cylinder internal parts, permit the master cylinder to be
removed by itself, leaving the power cylinder on the car.
1. Disconnect hydraulic lines at master cylinder, pump
fluid from cylinder into a container and dispose of
fluid. Cover openings in master cylinder and ends of
both pipes to prevent entry of dust, dirt, etc.
2. Remove master cylinder attaching nuts and lock
washers. Remove master cylinder from vacuum
power section.
POWER BRAKE VACUUM CYLINDER
-
REMOVE
1. Remove vacuum hose from front housing and discard
grommet. Remove master clyinder and position away
from power section. DO NOT disconnect fluid lines.
2. Remove clevis pin retainer from brake pedal inside
the car.
3. Remove nuts from vacuum cylinder studs under dash
and remove vacuum power section.
4. Clean exterior of power brake.
POWER UNIT
-
DISASSEMBLE (Fig. 58-5)
NOTE: Tools BT 7 C K 1 4 or J 23456 (Fig. 5B-6)
may be used for housing disassembly as an al-
ternate to the following method.
1. Using tool J 22805-0 1, mount power brake assembly
in vise, clamping on tool so that valve operating rod
is up.
2. Scribe a line across the front and rear housings to
facilitate reassembly.
3. Using tool J 9504, press down firmly and rotate tool
and housing clockwise so that cut-outs in rear hous-
ing line up with indentation of front housing.
WARNING: REMOVE REAR HOUSING CARE-
FULLY AS IT IS SPRING-LOADED AND WILL
TEND TO FLY AWAY FROM THE FRONT HOUS-
ING.