Operating Instructions Using the Brake System
Medium Duty
(R10/06) Y53-6008 – 77 –
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.
Trailer Park or Emergency Brake Application Only
If you ever have a failure or disconnect the air supply hose to
the trailer, the trailer parking brakes will set. The Red knob
will automatically pop OUT and seal off the tractor air reser-
voirs to protect the tractor air system pressure.
To apply the trailer brakes only:
Pull OUT the Red knob. This will exhaust air from the trailer
supply line, causing the tractor protection valve to close and
the trailer spring brakes to apply. The trailer is now in “emer-
gency” or “park.” This mode would be used to uncouple from
the trailer and during bobtail operation (running without a
trailer connected).
02393
SYSTEM PARK OR
CHARGE TRAILER
WITH TRACTOR PARKED
TRAILER
AIR
SUPPLY
PARKING
BRAKE
NORMAL OPERATING
POSITION
TRAILER
AIR
SUPPLY
PARKING
BRAKE
PARK TRAILER WITH
TRACTOR RELEASED OR
BOBTAIL TRACTOR
TRAILER
AIR
SUPPLY
PARKING
BRAKE
YELLOWRED
YELLOW
RED YELLOW
RED
