Chevrolet 70 1969 Series, Shop Manual

Page: 225 / 913

BRAKES 5B-32
with soap suds and check for leaks. Leakage is
caused by defective diaphragm, piston O-ring, or
seat.
c. If leakage is excessive, remove relay valve
and repair or replace with new valve.
R E L A Y V A L V E R E P L A C E M E N T
(Refer to Fig. 8)
Removal
Exhaust air pressure from air system. D is­
connect all air lines from valve. Remove mounting
bolts, then remove valve assembly from vehicle.
Installation
Mount valve on crossmember or bracket and
tighten mounting bolts firmly. Connect air lines to
valve, referring to "Air Lines" section for torque
specifications for air line fittings. Build up air
pressure in system, then test valve as directed
under "Serviceability Tests."
PRESSURE PROTECTION VALVE
The pressure protection valve is used as
standard equipment on all conventional cab models
in the 70 and 80 series. It is mounted in a
delivery port of the application valve. On other
series trucks it may be used with optional equip­
ment (air shift, differential lock, etc.). In the
optional application, it is located in the outlet air
line of air tank between air tank and optional
equipment.
The function of the valve is to close the air
lines to horns, wipers, transmission shift, differ­
ential lock, etc., when the pressure in the main air
system falls below 65 psi (- 5 lbs.). Thus, in the
event of pressure loss to 65 psi, there still will be
sufficient pressure left to apply service or emerg­
ency brakes and stop the vehicle.
R E P L A C E M E N T
Removal
1. Block vehicle wheels.
2. Exhaust: air pressure from system.
3. Disconnect air lines to valve.
4. Remove valve from port of application
valve (or air tank line).
Installation
1. Install valve in delivery port of applic ation
valve (or air tank line).
2. Connect air lines to valve.
3. Build up air pressure in system and check
for leaks.
4. Drain air pressure in system below 65 psi
and check to determine if valve has shut off supply
to applicable units.
QUICK RELEASE VALVE
Quick release valve is used as standard equip­
ment at both front and rear brakes on some models,
Figure 10— Moisture Ejector Valve Installed (Typical)
and at front brakes only on other models. The
purpose of the quick release valve is to reduce
the time required to release the brakes by hasten­
ing the exhaust of air pressure from the brake
chambers. The valve consists of a body cover and
diaphragm so arranged as to permit air pressure
to flow through the valve in one direction. When
application pressure is reduced, the air pressure
which has passed through the valve is permitted
to escape through the exhaust port.
S E R V IC E A B IL IT Y T EST S
1. Operating Test
Apply brakes, and observe that when brakes
are released, air pressure is exhausted freely
through the exhaust port of the valve. Be sure the
exhaust port is not restricted in any way.
2. Leakage Test
With brakes applied, coat the exhaust port
with soap suds to check leakage. Leakage is caused
either by dirt on exhaust seat, by a worn diaphragm,
or by a damaged exhaust seat on valve cover.
Q U IC K R E L E A S E V A L V E
R E P L A C E M E N T
Removal
Disconnect air lines from valve. Remove two
bolts attaching valve to crossmember or axle
bracket and remove valve assembly.
Installation
Mount valve on crossmember or axle bracket
and tighten mounting bolts firmly. Connect air lines
to valve, referring to "Air Lines" section for
torque specifications for air line fittings. Build up
air pressure in system, then test valve as direc­
ted under "Serviceability Tests."
CHEVROLET SERIE5 70-80 H EAVY DUTY TRUCK SH O P M A N U A L