Peterbilt 325 2017, Operator'S Manual

Page: 175 / 392

OPERATING THE BRAKE SYSTEM
Hydraulic Brakes
WARNING!
Do not operate the vehicle in the
event of a malfunction in any air or
hydraulic circuit. Such a malfunc-
tion may prevent the brake system
from operating properly, and could
result in an injury accident. The ve-
hicle should not be operated until the
system is repaired and both brak-
ing circuits, including all pneumatic,
hydraulic, and mechanical compo-
nents are working properly.
The operation of the vehicle's braking
system is based on the principle of
hydraulics. Hydraulic action begins
when force is applied to the brake
pedal. This force creates hydraulic
pressure in the master cylinder and is
amplified with assistance of a power
booster. The supplemental boost in
force is developed when pressurized
power steering fluid from the steering
pump presses on the master cylinder
piston. As a safety precaution, the
pressurized fluid from the master
cylinder has two mutually independent
circuits. The primary circuit supplies
the front wheels while the secondary
circuit supplies the rear wheels. The
displaced fluid from the master cylinder
travels through brake pipes terminating
at the wheel cylinders which actuate
the brake pad mechanisms. Actuation
of these mechanisms force the brake
pads against the rotors to stop the
wheels.
A reserve electric motor pump provides
a redundant power source for the
hydraulic booster in the event normal
flow from the power steering pump is
interrupted. Manual braking is also
available in the event both the power
and reserve systems are inoperative.
WARNING!
Never drive your vehicle with the
parking brakes applied. Always re-
lease the parking brakes prior to
moving the vehicle. Failure to dis-
engage the parking brakes prior to
moving your vehicle could result
in excessive heat build-up of the
brakes and start a fire.
NOTE
Today’s diesel electronic engines
have significant torque and starta-
bility power at low RPM. Combina-
tions of engine speed and available
torque may over-power the vehicle’s
parking brakes.
(03/17) Y53-6060-1C1
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