Chevrolet 10 Series 1968, Service Manual

Page: 334 / 713

BRAKES 5-91
4. Install automatic adjuster components as detailed in
applicable procedure.
5. Install wedge assembly in actuation housing (Refer to
Figure 131). Be sure rollers are seated correctly
in retainer cage and make good contact with plungers.
NOTE: Spring retainer washer has "ears" on
each side to be used as guides to assure correct
installation (See Figure 127). Housing has "slots"
to match "ears” on washer (See Figure 132).
6. Install brake shoes as previously described under
"Brake Shoe Installation" in this section.
7. Install brake chambers as described previously.
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") counterclockwise as far as it
will go (approximately 18 turns - See Figure 135).
Brakes are now in operating condition, either for
service brakes or parking.
11. After brakes are in operating condition, adjust brakes FI9* 132-W edge C a v ity in Housing ("Slots" Shown)
and repeat operating and leakage tests as previously
described.
“ FAIL-SAFE” BRAKES
GENERAL
The Stopmaster "Fail-Safe" is a mechanical actuation as well as a safety feature in the event of air brake
feature for power brakes and is two-fold in purpose. It failure,
is used as an air-released, spring-applied parking brake,
DESCRIPTION AND OPERATION
Brake Chambers (Fig. 133)
Two brake chamber assemblies are used at each wheel.
Type used differs by model as shown in Figure 126. The
"Fail-Safe" brake chamber assembly consists of an inner
and outer chamber. The inner chamber, containing a dia­
phragm and diaphragm plate rod, serves as the service
brake chamber and operates in the same manner as a
conventional brake chamber. Movement of diaphragm
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 chamber diaphragm
plate rod. During normal operation, constant air pres­
sure is applied to the outer chamber; this pressure, act­
ing on the piston, holds the 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 mechan­
ism, applying the brakes.
This same action will take place in the event air pres­
sure is lost from the system.
NOTE:
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 pressure in the
protected tank is depleted, brakes will remain applied un­
til air pressure is restored. If necessary to move the
vehicle before air pressure can be restored, brakes can
be released by turning the release bolts clockwise as far
as possible (approximately 18 turns) to compress the
springs, as shown in Figure 135. (This must be done at
all "Fail-Safe" chambers at each wheel.) After air pres­
sure has been restored, service brakes will be operative
immediately; however, the parking brake will remain in­
operative until the spring release bolts are backed out
(counter-clockwise) as far as possible to release the
springs. Push parking brake valve knob in to released
position to admit air pressure into the parking brake
chambers to hold springs compressed while turning the
release bolts.
INSTALLATION
“SLOTS”
CHEVROLET TRUCK SERVICE MANUAL