Pontiac FIREBIRD 1972 Service Manual page 480

TANDEM DIAPHRAGM POWER BRAKE-MORAINE 5D-3
Fig. 5 0 - 1 Construction of Delco Moraine Power Brake
anism, which consists of the air valve and push rod assem-
bly, (7) and the floating control valve assembly (8). The
air valve and push rod assembly is retained in the primary
power head piston by a snap ring. The floating control
valve assembly is held in place in the primary power piston
by the floating control valve retainer (9). A push rod
limiter washer (lo), located immediately behind the float-
ing control valve, is included to prevent the push rod from
contacting the plastic tube of the primary power piston.
The push rod ball is.permanently staked to the air valve;
the push rod eye end protrudes from the power head rear
housing through a filter element (1 I), located behind the
limiter washer, and a boot (12) containing a silencer (13).
The bead on the I.D. of the primary diaphragm (14) is
held in a sealed position on the primary power head piston
when the primary diaphragm support plate (15) is rotated
into a locked position on the primary power piston.
The primary power piston bearing (3) is located in the
center opening of the rear housing and provides a seal as
well as a sliding surface for the tubular section of the
primary power piston. A power head silencer (24) is posi-
tioned around the O.D. of the tubular section of the pri-
mary power piston.
The secondary power piston bearing (16) is posiitoned on
the I.D. of the housing divider (5). The threaded end of
the secondary power piston slides through the bearing in
the housing divider and screws into the primary power
piston.
The primary diaphragm is held in position on the O.D. of
the housing divider by stretching the bead on the O.D. of
the diaphragm and positioning it over the turned-up edge
of the divider. When the front and rear housings are
locked together, the housing divider is held in a stationary
position between the housings.
The secondary power piston contains the reaction mech-
anism, which consists of the reaction piston (17), the rub-
ber reaction disc (la), and the (plastic) piston rod retainer
(19). The piston rod retainer houses the piston rod (27)
which contacts the master cylinder primary piston. The
piston rod retainer is held in place by a retainer plate (20)
which is positioned on the "lug" end of the secondary
power piston and held in place by the power piston return
spring.
The unit is sealed when the housings are rotated into a
locked position.
A front housing seal (2) is located in the depression in the
front housing. A vacuum check valve assembly is located
in the front housing for connection to the vacuum source.
Two fluid reservoirs (30) are integrally cast with the mas-
ter cylinder body and supply fluid to the spaces between
the primary and secondary seals through the drilled com-
pensating holes (31) in the casting.
Within the bore of the master cylinder is the primary
piston assembly (34), which includes a secondary seal
(33), primary seal (35), primary seal protector, spring re-
tainer (36), primary piston spring (37), secondary piston
stop (39), and piston extension screw (38). The secondary
piston assembly (41) includes two secondary seals (40), a
primary seal (42), primary seal protector, spring retainer
(44), and secondary piston spring (45).
The reservoir diaphragm (29) and cover (28) provide pro-
tection from contamination of the brake fluid. A stop