4-22. AIR SYSTEM - Continued
4-22.8 Service Brake Valve - Continued
Brush the brake pedal and connectors with
a soap solution while applying the brake.
No leakage is permitted. Tighten/remake
joints as required.
Release brake pedal and then slowly apply.
Check that both pressure gages have
similar readings and both show a reading
proportional to the movement of the brake
approximately 2 psi (14 kPa) greater than
From full application, release pedal and
check pressure falls to zero promptly.
Stop main engine, set battery switch to
Drain pressure from all air tanks via the
Disconnect the temporary pressure gages and install the stop light switches (8).
Connect wires to all pressure switches mounted on the foot brake. Be sure they are connected exactly
as noted in REMOVAL step 1.
Restart main engine and ensure stop lights illuminate when brake is applied and low air alarms cease when
air tanks are at full pressure.
Normal procedure is to replace the brake valve assembly if malfunctioning. In an emergency, it may
be repaired as per the following procedures.
The brake valve does not have to be removed from the truck to repair the internal mechanism (see
REMOVAL steps 7. thru 11. only).
Remove O-rings (2 and 3).
Remove retaining ring (17), and remove No 2 circuit inlet exhaust assembly (1).
Apply firm pressure on spring seat (19), which will compress piston return spring. Locking groove in piston
(25) is now accessible through rectangular opening in lower static piston body (24) Insert wire or
screwdriver into locking groove, thus holding static piston spring in compressed position.