Air Brake System
General Information
A dual air brake system consists of two independent air
brake systems which use a single set of brake controls.
Each system has its own reservoir, plumbing, and brake
chambers. The primary system operates the service
brakes on the rear axle; the secondary system operates
the service brakes on the front axle. Service brake sig-
nals from both systems are sent to the trailer.
WARNING
Do not operate the vehicle with the front brakes
backed off or disconnected. Backing off or discon-
necting the front brakes will not improve vehicle
handling and may lead to loss of vehicle control
resulting in property damage or personal injury.
Loss of air pressure in the primary system causes the
rear service brakes to become inoperative; front brakes
will continue to be operated by secondary system air
pressure. In addition, trailer brakes will be operated by
the secondary system.
Loss of secondary system air pressure causes the front
axle brakes to become inoperative; rear service brakes
and trailer brakes will be operated by the primary sys-
tem.
Before driving your vehicle, allow time for the air com-
pressor to build up a minimum of 95 psi (655 kPa) pres-
sure in both the primary and secondary systems. Moni-
tor the air pressure system by observing the dual
system air pressure gauge and the low-air-pressure
warning light and buzzer. The warning light and buzzer
shut off when air pressure in both systems reaches 64
to 76 psi (441 to 524 kPa).
The warning light and buzzer come on if air pressure
drops below 64 to 76 psi (441 to 524 kPa) in either sys-
tem. If this happens, check the air system pressure
gauges to determine which system has low air pres-
sure. Although the vehicle’s speed can be reduced us-
ing the foot brake control pedal, either the front or rear
service brakes will not be operating, causing a longer
stopping distance. Bring the vehicle to a safe stop, and
have the air system repaired before continuing.
WARNING
Do not drive the vehicle with the parking brakes
caged. If the vehicle is driven with the parking
brakes caged, there would be no means of stopping
the vehicle if a complete loss of air pressure oc-
curred. This could result in serious personal injury
or vehicle damage. Before caging the spring park-
ing brakes, make the connection to a towing vehicle
or chock the tires.
Brakes
7.1
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