Chevrolet 10 Series 1968, Service Manual

Page: 308 / 713

BRAKES 5-65
F ig . 9 8 -A ir Brake Control V a lv e
1. Screw
2 . Retainer
3 . Diaphragm
4 . Ring
5. Exhaust V a lv e Body
6. Seal
7 . Spring
8 . Seal
9. V a lv e
10. V a lv e Body
11. Spring
12. Seal
13. Sea I
14. Piston Assembly
15. Snap Ring
16. Mounting Bracket
17. Plunger
18. Boot
19. Bolt
20. Lock Washer
Tests and Adjustments of Rebuilt Unit
Tests
If facilities are available, the rebuilt brake valve can
be tested on a suitable test rack. If such facilities are
not available, the brake valve can be tested on the
vehicle.
Both operating and leakage tests must be made in
either case to make certain the brake valve meets the
following specifications:
1. The brake valve must deliver approximately full
reservoir pressure when the pedal is fully de­
pressed. If this test is being made on a vehicle and
brake valve does not deliver approximately full
reservoir pressure, check to see if the pedal ad­
justment linkage is causing any interference.
2. The brake valve must control delivered pressures
between approximately 5 and 75 psi» These pres­
sures must rapidly vary in accordance with the
position in which the pedal is held.
3. Leakage at the exhaust port in both the fully applied
or fully released positions must not exceed a one-
inch soap bubble in three seconds.
4. No leakage is permissible at any other point on the
brake valve with the pedal in the depressed position.
Adjustments
If the brake valve does not release promptly, or does
not fully release, it indicates that the exhaust valve is
not operating sufficiently. This can be caused by :
1. Insufficient exhaust valve to valve seat clearance.
2. Improper adjustment of the brake pedal push rod.
3. Lack of lubrication in the body causing the piston
and spring assembly to bind.
4. Binding pedal and/or linkage.
If the brake valve does not apply promptly, or does not
apply fully, it indicates that the inlet valve is not opening
sufficiently. This can be caused by:
1. Improper adjustment of the linkage, which does not
permit the piston to travel far enough when the brake
is being applied.
2. Binding pedal and/or linkage.
If the brake valve does not graduate the delivered pres­
sure properly check to be sure the bleed hole to the
cavity immediately below the piston is not restricted.
Installation
1. Mount brake valve in position, install mounting bolts
and tighten.
2. Connect air lines to brake valve.
3. Test operation thoroughly.
4. Adjust brake pedal free play as outlined in this
section under Push Rod to Main Cylinder Adjustment.
QUICK RELEASE VALVE
Removal
1. Disconnect air lines at quick release valve (fig. 99).
2. Remove mounting bolts and remove valve.
F ig . 9 9 -Q u ic k Release V a lv e Installed
CHEVROLET TRUCK SERVICE MANUAL