Chevrolet 70 1969 Series, Shop Manual

Page: 252 / 913

BRAKES SB-59
2. Install plungers and seals in housing as
shown in figure 32.
N O T E : Installation tool shown in figure 32 can
be made locally according to dimensions shown in
figure 33.
3. Insert plunger guide with new washer inside
slots in anchor plungers.
4. Install automatic adjuster components as
detailed in applicable procedure.
5. Install wedge assembly in actuation housing
(refer to fig. 34). Be sure rollers are seated cor­
rectly in retainer cage and make good contact with
plungers.
N O T E : Spring retainer washer has "ears" on
each side to be used as guides to assure correct
installation (see fig. 30). Housing has "slots" to
match "ears" on washer (see fig. 35).
6. Install brake shoes as previously described
under "Brake Shoe Installation" in this section.
7. Install brake chambers as described pre­
viously.
8. Connect all air lines into both chambers.
9. Build up air pressure in system and push
parking brake knob in to admit air into outer
chambers (with "Fail-Safe" only).
10. With air in outer chambers, turn release
bolt at each chamber (if "Fail-Safe") counterclock­
wise as far as it will go (approximately 18 turns -
“FAIL-SJ
GENERAL
The Stopmaster "Fail-Safe" is a mechanical
actuation feature for power brakes and is two-fold
in purpose. It is used as an air-released, spring-
applied parking brake, as well as a safety feature
in the event of air brake failure.
DESCRIPTION A N D OPERATION
BR AKE C H A M B E R S (Fig. 36)
Two brake chamber assemblies are used at
each wheel. Type used differs by model as shown
in figure 23. The "Fail-Safe" brake chamber as­
sembly consists of an inner and outer chamber.
The inner chamber, containing a diaphragm and
diaphragm plate rod, serves as the service brake
chamber and operates in the same manner as a
conventional brake chamber. Movement of dia­
phragm plate rod is transmitted to the brake shoes
through the mechanical actuating components as
described later.
The outer chamber contains a spring-loaded
piston which acts against the service brake cham­
ber diaphragm plate rod. During normal operation,
constant air pressure is applied to the outer cham­
ber; this pressure, acting on the piston, holds the
Figure 35— W edge Cavity in Housing (“Slots" Shown)
see fig. 38). Brakes are now in operating condition,
either for service brakes or parking.
11. After brakes are in operating condition,
adjust brakes and repeat operating and leakage
tests as previously described.
BRAKES
spring compressed. When air pressure is released
from the outer chamber by pulling out the knob on
the parking brake control valve, spring pressure
forces the piston toward the service brake cham­
ber; piston movement is transmitted through the
service brake diaphragm plate rod to the brake
actuating mechanism, applying the brakes.
This same action will take place in the event
air pressure is lost from the system.
N O T E : The air tank supplying air pressure
to the parking brake chambers is protected from
the main air system by a one-way check valve;
this tank will contain enough pressure for at least
one parking brake release in case pressure is lost
from the main air system.
In case of complete pressure loss, and pres­
sure in the protected tank is depleted, brakes will
remain applied until air pressure is restored. If
necessary to move the vehicle before air pressure
can be restored, brakes can be released by turn­
ing the release bolts clockwise as far as possible
(approximately 18 turns) to compress the springs,
as shown in figure 38. (This must be done at all
"Fail-Safe” chambers at each wheel.) After air
pressure has been restored, service brakes will
be operative immediately; however, the parking
CHEVROLET SERIES 70-80 H EAVY DUTY TRUCK SH O P M AN U AL