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

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 buildup
of the brakes and start a fire.
Introduction
NOTE: If your truck is equipped with hydraulic
brakes, go to page 88.
The operation of the vehicle's braking system and many vehicle
accessories depends upon the storage and application of
a high-pressure air supply.
Operating Instructions
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 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 injury accidents.
– 72 – Y53-6008 Medium Duty (R10/06)