Chevrolet 30 Series 1967 Service Manual page 277

Leakage Tests
1. Apply truck brakes and check for leakage at hand
control valve exhaust port, using soap suds.
2. Apply trailer brakes only with hand control valve
and check for leakage at truck brake application
valve exhaust port, using soap suds.
3. Leakage of a one inch bubble in one second is per­
missible in either of these tests. If leakage exceeds
this specification, replace the shuttle valve.
EMERGENCY AIR VALVE AND
BREAKAWAY VALVE
Operating Tests
1. Pull out emergency air valve knob to exhaust air
pressure from breakaway valve control line. Dis­
connect trailer emergency line from emergency out­
let port at breakaway valve and connect an air
pressure test gauge to emergency outlet port.
2. Start engine and build up air pressure in system.
Low air pressure buzzer should stop operating at
approximately 60 psi. With air pressure in operating
range, push emergency air valve knob in. Test gauge
1. Bolt
2. Lock Washer
3. Bracket
4. End Cap
5. Seal
6. N ut
7. V a lv e Disc
Fig.
99—A irbrake Hand Control V a lv e
8. V a lv e Body
9. V a lv e Return Spring
10. V a lv e Spring Retainer
11. Piston Return Spring
12. Piston Cup
13. Piston
should show full air system pressure. Then pull knob
out; test gauge should drop to zero.
3. Again build up air pressure in system to operating
range, then stop engine. Push emergency air valve
knob in. Make a series of brake applications until
low air buzzer sounds. Slightly open drain cock in
the dry air tank to obtain a slow (approx.
minute) pressure drop in the tractor brake system.
When truck air system drops to 45 psi (approx.) the
emergency air valve knob should automatically come
out and pressure on test gauge should rapidly drop
to zero.
Leakage Tests
1. Build up air pressure in truck brake system to oper­
ating range. Push in emergency air valve knob to
charge trailer brake system. Use soap suds to coat
exhaust ports of emergency air valve and breakaway
valve.
2. When emergency air valve leaks excessively, install
new piston O-rings. When breakaway valve leaks
excessively, install new O-rings and plunger seal.
14. Spring
15. Cam
16. Cam Shaft
17. Cam Housing
18. Adjusting Bearing
19. C o lla r
BRAKES 5-63
psi per
1 0
20. C over
21. N u t
22. Operating Lever
23. Name Plate
24. Lock Washer
25. Screw
CHEVROLET TRUCK SERVICE MANUAL