Peterbilt Medium Duty Truck Owner's Manual - Peterbilt Motors

USING THE BRAKE SYSTEM
WARNING! Do not use the trailer hand brake
or service brakes to park and hold an unattended
vehicle—use the parking brakes.
Because service brakes work with air pressure,
these brakes could slowly release. Your
vehicle could roll, causing a serious accident.
Someone could be hurt or killed. Never rely on
the service brakes to hold a parked vehicle.
Parking Tractor and Trailer
• With both knobs pushed in for normal operating
modes, the parking brakes of both the tractor and the
trailer may be applied by pulling the Yellow knob OUT.
This will exhaust the air from the tractor spring brakes,
and simultaneously cause the Red knob to pop OUT,
which will apply the trailer brakes. This complies with
the FMVSS 121 requirement that one control should
apply all the parking brakes on the vehicle.
STARTING AND OPERATING THE VEHICLE
Trailer Charge
• If both knobs are OUT (combination vehicle is
parked), and it is desired to recharge the trailer, the
Red knob may be pushed IN to repressurize the trailer
supply line. The tractor will remain parked. For more
information on air supply pressure requirements, see
page 108.
Brake Safety and Emergency
WARNING! Do not operate the vehicle in the
event of a malfunction in any air circuit. The
vehicle should not be operated until the system
is repaired and both braking circuits,
including all pneumatic and mechanical components,
are working properly. Loss of system
air can cause the service brakes to not
function resulting in the sudden application of
the spring brakes causing wheel lock-up, loss
of control, or over-take by following vehicles.
You could be in an accident and killed or
severely injured.
– 110 – Y53-6027 Medium Duty (R05/09)