Chevrolet 70 1969 Series, Shop Manual

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BRAKES 5B-64
the piston when the "Fail-Safe" is actuated and
keeps the unit sealed from direct atmospheric
contamination.
The "Fail-Safe" is used as an air-released,
spring-applied parking brake, as well as a safety
feature in the event of air brake failure.
SAFETY PRECAUTIONS
When brakes are equipped with Super
"F a il-S a fe " units, cage the power spring
before starting any disassem bly or re­
moval of wheels or drum s to avoid possible
injury.
When a vehicle is disabled, due to low
or lost a ir pressure, block the wheels and
cage the power sprin g before attempting
to move the vehicle.
SERVICE RECOMMENDATIONS
C A G IN G A N D U N C A G IN G P O W E R SPRING
On the Super "Fail-Safe" the head of the re­
lease bolt is exposed at all times.
The power spring is caged by rotating the re­
lease bolt 18 to 21 full turns clockwise. Do not
force the bolt beyond its normal stop.
Both the caging and uncaging operation can be
made easier by applying air pressure (65 psi min­
imum) to the "Fail-Safe." This will take the spring
load off the release bolt.
D IS A S S E M B L Y (Refer to Fig. 44)
1. Cage power spring by turning release bolt
18 to 21 turns clockwise.
2. Remove "Fail-Safe" from non-pressure
housing at clamp ring.
3. Release foot set screw.
4. Unscrew foot from piston.
5. Remove piston seal.
6. Remove sealing' compound located at joint
between cap and housing.
7. Remove lock ring from housing.
8. Separate cap, spring and piston assembly
from housing. Remove rubber seal from housing.
9. Remove back-up rings and O-ring from
groove in housing.
10. Remove snap ring and hex nut from re­
lease bolt.
11. Secure cap, spring and piston assembly
in fixture.
N O T E : Refer to figure 45 for illustration of
fixture. This fixture is necessary to hold the power
spring in compression for disassembly. It can be
made locally from common materials.
12. Turn release bolt until square nut falls
free.
13. Release pressure on fixture until spring
is unloaded.
14. Remove assembly from fixture.
15. Separate cap from spring and piston as­
sembly.
16. Remove back-up ring and O-ring from
piston.
17. Remove the two spring bearing washers.
18. Remove " E " ring from release bolt.
6 7 8 9 10
21 20 19 18 17 16 1514 13 12 11
1 Non-Pressure 11 Release Bolt
Housing 12 Cap
2 Clamp Band 13 Power Spring
3 Foot 14 Back-up Ring
4 Piston Seal 15 O-ring
5 Hex Nut 16 Piston
6 Fail-Safe Housing 17 Setscrew
7 Square Nut 18 Diaphragm
8 Rubber Seal 19 Push Rod
9 Lock Ring 20 Wedge Guide
10 Breather Assembly
21 Wedge T-5922
Figure 42— Brake Assembly with Super “Fail-Safe”
Figure 43— Super “Fail-Safe" Assembly
CHEVROLET SERIES 70 -80 H EAVY DUTY TRUCK SH O P M A N U A L