OPERATOR'S MANUAL

Operating Instructions Using the Brake System
Model 330 PB1318 3/01 – 73 –
The parking brakes act on the rear wheels only. They are
spring-applied, with air pressure used to release them.
Release air is supplied by both the front and rear circuit res-
ervoirs through a double check valve.
To release the truck or tractor parking brakes ONLY:
• Push IN the Yellow knob on the dash. Your trailer will
remain parked.
Below 60 psi (414 kPa) the Yellow parking brake valve
remains OUT (ON position). If air pressure is not
restored above 60 psi (414 kPa), the knob will automati-
cally return to the OUT position if you attempt to push it
in. See
page 25 for more information.
To release the trailer brakes ONLY:
• Push IN the Red knob on the dash. The truck or tractor
will remain parked.
To release the full combination of brakes:
• Push IN
BOTH knobs on the dash.
• In the event that air pressure is reduced below a safe
level: the low air warning light will come on first; if air
pressure continues to drop, the parking brake valve will
pop OUT, automatically applying the spring brakes.
CAUTION: Do not try to put the vehicle in
motion before pressure in the system reaches
100 psi (689 kPa) because the wheels are
locked by the spring brake action.
• Unnecessary stress and possible brake mal-
function could occur if the vehicle is forced to
move before the air system reaches 100 psi (689
kPa).
• Below 60 psi (414 kPa) the parking brake valve
button remains in the applied (ON) position. If air
pressure is not restored, the button will automat-
ically return to its initial position.
Combination (Tractor/Trailer) Parking Brake Control Valves
(2) Trailer Air Supply
Control (Red)
(1) Parking Brake Control
(Yellow)
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