Peterbilt Medium Duty Truck Owner's Manual - Peterbilt Motors

USING THE BRAKE SYSTEM
Using the Brake System
NOTE: Today’s diesel engines have significant
torque and startability power at low RPMs. Combinations
of engine speed and available torque
may overpower the vehicle’s parking brakes.
WARNING! Never drive your vehicle with the
parking brakes applied. Always release the
parking brakes prior to moving the vehicle.
Failure to disengage the parking brakes prior
to moving your vehicle could result in excessive
heat build-up of the brakes and start a
fire, possibly resulting in death, personal
injury or property damage.
NOTE: If your truck is equipped with hydraulic
brakes, go to page 121.
The operation of the vehicle's braking system and many
vehicle accessories depends upon the storage and application
of a high-pressure air supply.
This air brake system is a multiple circuit type: it has a circuit
for the front wheels, a separate circuit for the rear
wheels, and one for the trailer (tractors only). The system
STARTING AND OPERATING THE VEHICLE
is supplied by a compressor driven by the engine. The
vehicle's compressor takes outside air and compresses it,
usually to 100–130 psi (690–896 kPa). This compressed
air then goes to the reservoirs to be stored until needed.
When you operate your air brakes, the stored compressed
air flows into the chambers where it is used to apply your
truck and trailer brakes. That is why, when you push down
on the brake pedal, you do not feel the same amount of
pressure on the pedal that you do when you apply the
brakes on your car. All you are doing on your truck is
opening an air valve to allow air to flow into the brake
chambers.
WARNING! The brake system is a critical vehicle
safety system. For the safety of you and
others around you, have the vehicle submitted
for periodic preventive maintenance checks
as well as having any suspected problems
immediately checked by an Authorized Service
Center. Failure to properly maintain your
brake system can lead to serious accidents
involving death or personal injury.
– 104 – Y53-6027 Medium Duty (R05/09)