User Manual

takes outside air and compresses it,
usually to 100-130 psi (689-896 kPa). The
compressor air then goes to the air tanks
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 antilock brake system is a critical
vehicle safety system. For the safety
of you and others around you, have
the vehicle submitted for periodic pre-
ventive maintenance checks as well as
having any suspected problems imme-
diately checked by an authorized deal-
er. Failure to properly maintain your
brake system can lead to serious acci-
dents. Failure to comply may result in-
property damage, personal injury, or
death.
WARNING
Never drive your vehicle with the park-
ing
brake applied. Always release the
parking brakes prior to moving the ve-
hicle. Failure to disengage the parking
brakes prior to moving your vehicle
could result in excessive heat buildup
in the brake system, resulting in a fire.
Failure to comply may result in proper-
ty damage, personal injury, or death.
NOTE
Today's diesel engines have significant
torque
and startability power at low
rpm. Combinations of engine speed
and available torque may over-power
the vehicle's parking brakes.
Front Brake System
When the brake pedal is depressed, the
front circuit portion of the treadle valve
delivers air from the front service air tank to
the front axle brake chambers via a quick-
release valve.
Simultaneously (on full truck
configurations), air is also supplied to the
modulating valve control port. In the event
of a rear service circuit failure, the
modulating valve will exhaust air from the
spring brake chambers, applying the spring
brakes in proportion to the front circuit
application.
Rear Brake System
When the brake pedal is depressed, the
rear circuit portion of the treadle valve
delivers air from the rear service air tank to
the service brake relay valve control port.
The relay valve then delivers air directly
from the rear service air tank to the rear
brake chambers in proportion to the treadle
pressure.
Using the Parking Brake
The yellow diamond-shaped knob on the
dash controls the vehicle parking brakes.
These are spring brakes that you activate
by releasing air pressure from their
chambers. When they are not in use, air
pressure compresses the springs and
releases the brakes. Pulling the valve OUT
applies the parking brake, which exhausts
air from the chambers and allows the
springs to extend and apply the brakes.
DRIVING - Air Brake System (option)
136 Y53-6113-1A1 (11/20)
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