operators_manual

Compressed air is delivered to the brake
system through the valve at the brake
pedal and is controlled with various valves
and braking circuits. The brake system is
designed with separate front, rear and
(when applicable) trailer circuits so that if
one circuit is compromised and loses air,
the other circuits will not be affected.
Safety valves in each circuit will protect the
other circuits in the event that a circuit
loses air.
The air compressor on the engine will
typically provide 100-130 psi (690-896
kPa) to the air tanks. The vehicle is also
designed with an air dryer, which removes
moisture from the compressed air in order
to protect all components in the air system.
The brake system may be further
enhanced by additional devices such as
brake proportioning valves, Anti-lock
braking systems or sensors designed to let
you know if your brake pads need to be
serviced. Certain conditions may result in
the brake surfaces getting wet. Brake
surfaces that are wet do not perform as
well as when they are dry. There may be
situations where wet brake surfaces cannot
be avoided. In such situations, apply the
brakes while in motion, to dry the brake
surfaces.
Certain conditions may result in your brake
surfaces becoming overheated (above
800°F or 427°C). Overheated brakes will
damage linings and drum surfaces,
ultimately decreasing braking performance.
Refer to Retarders and Descending a
grade to avoid overheating the brakes.
Parking Brake
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1. Normal Run Position
2. Trailer Park with Vehicle Released
3. System Park or Trailer Charge with
Vehicle Parked
Parking brakes work in reverse action of
the regular brakes. When the parking
brakes are engaged, air is exhausted from
the spring chambers, which allows the
spring to engage the brakes. This design
also provides a safety function if a brake
circuit has a leak and loses air. In such a
scenario, the parking brakes will apply.
The vehicle’s parking brake controls are
the yellow diamond shaped knob on your
dash board. If the vehicle is equipped to
tow a trailer, then there will be an additional
red octagon shaped knob for the trailer
parking brakes. Parking brakes will be
engaged when either of these knobs are
pulled OUT. (If one knob is pulled out, the
other knob will automatically pop out.)
Pushing IN a knob will disengage the
respective parking brakes. If you push in
the yellow knob only, you will disengage
the vehicle’s parking brakes but will not
disengage the trailer parking brakes (if
applicable). Either knob will pop back out if
the system pressure is not above 60 psi
(414 kPa). The instrument panel display
will provide a message any time the
parking brakes (vehicle or the trailer) are
set and the vehicle is put into motion.
DRIVING - Brakes
Y53-6047-2HEN (03/18) 147
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