Chevrolet 30 Series 1967 Service Manual page 276

BRAKES 5-62
2. Mount backing plate-gauge assembly in instrument
panel.
3. Replace lamp socket and gauge line.
4. Thoroughly check gauge connection for leakage.
PRESSURE PROTECTION VALVE (Fig. 97)
Disassembly
1. Remove four screws and separate the upper and
lower bodies.
2. Remove diaphragm, spring cap and spring.
For 1967 trailer air brake equipment is available for
some models. The option includes a hand control valve,
double check valve, emergency air valve, breakaway
HAND CONTROL VALVE
Operating Tests
1. Check the delivery pressure of the valve, using an
accurate test gauge connected to the trailer brake
service line at the back of the cab. With air system
fully charged, and with valve operating handle in
fully applied position, test gauge should show the
same pressure (within 5 pounds) as registered on the
dash air gauge.
2. Move the handle to several positions between fully
released and fully applied and note that pressure
registered on the test gauge varies in accordance
with the position of the handle.
Leakage Tests
1. Coat the exhaust port with soap suds with operating
handle in fully released position to check for leakage.
Leakage in excess of a 1-inch bubble in one second is
not permissible. Leakage evidenced by this test is
DOUBLE CHECK
VALVE A N D
STOPLIGHT SWITCH
TO SERVICE
TANK
TRAILER EQUIPMENT
GENERAL DESCRIPTION
OPERATION TEST AND LEAKAGE TESTS
H A N D CONTROL
VALVE
TO SERVICE
BRAKE
Fig . 98—T ra ile r Equipment C ircu its
Cleaning and Inspection
1. Wash all parts in cleaning fluid.
2. Inspect diaphragm for cuts and punctures. Some in­
dentation of the diaphragm by the seat in the lower
body is normal.
Assembly
1. Position diaphragm, spring cap and spring on lower
body.
2. Align upper body with lower body, install four screws
and secure.
valve, trailer connectors, separate stop light switch and
connecting lines, (fig. 98). Testing and servicing of these
units is outlined in this section.
probably caused by a worn or deteriorated inlet valve
seal, or binding or corrosion between the valves and
valve guides in valve cage, preventing the inlet valve
from fully closing.
2. With operating lever in fully applied position coat
exhaust port with soap suds. Leakage evidenced by
this test may be due to a worn or deteriorated ex­
haust valve seal or by leaking piston seals.
DOUBLE CHECK VALVE
Operating Tests
1. Apply truck brakes and note that the brakes apply
promptly on both the truck and the trailer. Release
truck brakes and note that brakes on truck and
trailer both release promptly.
2. Move hand control valve lever to applied position
and note that brakes apply only on the trailer. Move
control valve lever to released position and note that
trailer brakes release promptly.
EMERGENCY
AIR VALVE
BREAKAWAY
VALVE
TRAILER
CO NNECTORS
CHEVROLET TRUCK SERVICE M ANUAL