Peterbilt Medium Duty Trucks Operator's Manual after 1-07

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.
Trailer Charge
Operating Instructions
• 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 76.
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 overtake
by following vehicles. You could be in an
accident and severely injured.
– 78 – Y53-6008 Medium Duty (R10/06)