Medium Duty Operator's Manual - Peterbilt Motors Company
Medium Duty Operator's Manual - Peterbilt Motors Company
Medium Duty Operator's Manual - Peterbilt Motors Company
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USING THE BRAKE SYSTEM<br />
to the trailer, and (3) protect the tractor air supply in case<br />
of separation of the air lines connecting the tractor to the<br />
trailer.<br />
Hydraulic Brakes<br />
WARNING! Do not operate the vehicle in the<br />
event of a malfunction in any air or hydraulic<br />
circuit. Such a malfunction may prevent the<br />
brake system from operating properly, and<br />
could result in an injury accident. The vehicle<br />
should not be operated until the system is<br />
repaired and both braking circuits, including<br />
all pneumatic, hydraulic, and mechanical<br />
components are working properly.<br />
The operation of the vehicle's braking system is based on<br />
the principle of hydraulics. Hydraulic action begins when<br />
force is applied to the brake pedal. This force creates<br />
hydraulic pressure in the master cylinder and is amplified<br />
with assistance of a power booster. The supplemental<br />
boost in force is developed when pressurized power steering<br />
fluid from the steering pump presses on the master<br />
cylinder piston. As a safety precaution, the pressurized<br />
fluid from the master cylinder has two mutually independent<br />
circuits. The primary circuit supplies the front wheels<br />
STARTING AND OPERATING THE VEHICLE<br />
while the secondary circuit supplies the rear wheels. The<br />
displaced fluid from the master cylinder travels through<br />
brake pipes terminating at the wheel cylinders which actuate<br />
the brake pad mechanisms. Actuation of these mechanisms<br />
force the brake pads against the rotors to stop the<br />
wheels.<br />
A reserve electric motor pump provides a redundant<br />
power source for the hydraulic booster in the event normal<br />
flow from the power steering pump is interrupted. <strong>Manual</strong><br />
braking is also available in the event both the power and<br />
reserve systems are inoperative.<br />
WARNING! Never drive your vehicle with the<br />
parking brakes applied. Always release the<br />
parking brakes prior to moving the vehicle.<br />
Failure to disengage the parking brakes prior<br />
to moving your vehicle could result in excessive<br />
heat build-up of the brakes and start a<br />
fire.<br />
NOTE: Today’s diesel electronic engines have<br />
significant torque and startability power at low<br />
RPM. Combinations of engine speed and available<br />
torque may over-power the vehicle’s parking<br />
brakes.<br />
– 118 – Y53-6008A <strong>Medium</strong> <strong>Duty</strong> (R05/09)
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