Chevrolet 70 1969 Series, Shop Manual

Page: 256 / 913

BRAKES 5B-63
5. Inspect piston seal for cracking or deter­
ioration. Inspect expander and expander retaining
plate for deterioration. Replace piston assembly
if necessary.
6. Inspect pressure housing for scratches,
scores, or excessive wear. Examine all parts for
obstructions and remove any foreign matter.
7. Examine spring in cap for deterioration or
rust. Inspect release bolt for signs of rust on
threaded portion. Unless spring or bolt is in very
bad condition, replacement should not be neces­
sary. See "Caution" in step 10 of "Removal and
Disassembly," previously.
8. Discard O-ring and rubber washer. Replace
with new parts.
9. Examine diaphragm plate rod boot (in non­
pressure housing) for deterioration or cracks. If
deterioration or other damage is evident, replace
as follows:
a. Pull diaphragm plate rod, wedge rod guide
and boot out of wedge rod and mounting tube re­
spectively.
b. Remove guide and boot from diaphragm
plate rod and install new boot on plate rod. Re­
place wedge rod guide.
c. Apply a liberal amount of rubber cement
to boot flange and mating surface on non-pressure
housing.
d. Position plate rod on wedge rod and hold
rubber boot flange tightly against housing surface.
Flange should seal tight to keep any moisture or
foreign matter from falling into actuation com ­
ponents.
N O T E : Be careful not to disturb wedge and
roller mechanism inside actuation housing when
repositioning plate rod on wedge rod.
BRAKE C H A M B E R A S S E M B L Y
A N D IN S T A L L A T IO N
Refer to figure 36 (also refer to figure 37 for
components).
Figure 41— “Strap" Type Wrench Dimensions
1. Install O-ring in groove in pressure housing.
2. Install piston assembly in cap assembly.
3. Position rubber washer in pressure housing
at bottom of internal threads. Thread cap and
spring assembly into pressure housing and tighten
firmly against rubber washer. This may be done
with "strap" type wrench (see figures 40 and 41)
or by putting pressure housing in vise and using a
wrench on hex end of cap.
4. Position diaphragm over plate rod, then in­
stall pressure housing and cap assembly.
N O T E : Diaphragm should fit evenly between
pressure housing and non-pressure housing. Align
marks made on housings at disassembly to insure
proper air port location.
5. Pull clamping ring over flange of pressure
and non-pressure housings. Install clamp bolt and
nut and tighten firmly.
6. Connect all air lines and build up air pres­
sure in system to normal operating pressure. Push
parking brake knob in to admit air to outer brake
chamber.
7. Turn release bolt counterclockwise as far
as possible (approx. 18 turns) to release spring
(see fig. 38). This will leave the parking brake
chamber in operating condition.
N O T E : It is best to have at least 60 psi of air
in chamber to hold spring tension off nut so a bet­
ter "feel" is obtained when the nut does bottom.
SUPER "FAIL-SAFE” BRAKES
The Super "Fail-Safe" Brake is identical to
the Standard "Fail-Safe" Brake in operation and
principle but differs physically in size and com­
ponents. Refer to Figure 42 for illustration of
complete Stopmaster brake assembly with Super
"Fail-Safe" chamber.
The Super "Fail-Safe" is a spring-powered
brake actuator that mounts "piggy-back” on the air
chamber non-pressure housing of the Stopmaster
brake (see fig. 43).
When 65 psi or more of air pressure is applied
against the piston, the power spring will be held in
a compressed position. When air pressure is re­
moved, the power spring will push the piston against
the diaphragm plate. The wedge head will be push­
ed deeper between the rollers spreading the plung­
ers apart and applying the brake.
The unit is equipped with a manual release
bolt to permit safe handling for service. The cap
cavity is sealed by an O-ring on the release bolt.
An internal venting system working in con­
junction with a one-way breathing arrangement on
the cap allows system air to fill the vacuum behind
CHEVROLET SERIES 70 -80 H EAVY DUTY TRUCK SH O P M A N U A L