Operation
• Downhill speed is controlled by removing one’s foot from the
accelerator pedal (engine running with closed throttle) and
putting the transmission/rear axle in reduced gear. If the
transmission/rear axle is in a gear that results in more than
the appropriate speed, a proper downshift should be made
to avoid overuse of the brakes. If the proper gear selection
was not made and the brakes were overused, then stop the
vehicle and wait for the brakes to cool. After the brakes have
cooled, continue down grade in a lower gear range.
• The common rule to follow in using the engine and
transmission/rear axle to control vehicle speed is to select
a lower gear going down the hill than would be required to
ascend the hill. There are some exceptions, such as going
down a short hill with good visibility and no hazards.
• The service brakes should be used to supplement available
vehicle retardation methods. When descending long grades
requiring use of the brakes, short applications (three to
five seconds duration) should be made rather than long,
continuous applications. This minimizes temperature rise,
brake fade, and air consumption of air brake system.
Air Brakes
WARNING
Stopping distance may increase under the failed
condition since only one section of the brake
system is operating. Reduce speed and employ
safe driving practices. Have brake system
repaired immediately. Loss of braking capability
could cause an accident and result in property
damage, personal injury, or death.
NOTE: The function of the air compressor is to provide and
maintain air under pressure to supply the air brake system and
other air powered devices. Certain air compressors in vehicles
with MaxxForce® 11 and 13 engines, while in operation, may
cause fluctuation of the needle in the air pressure gauge.
The truck types covered in this manual are equipped with a split
brake system.
The purpose of this split system is to provide a means of
stopping the vehicle should a failure occur in either the primary
or secondary brake system. In the event air pressure loss
occurs in one system, the remaining system continues to
provide braking action.
When a failure is detected, the air dryer is provided with a limp
homefeaturetoallowthevehicletobedriventoaservicecenter.
If vehicle has been parked for an extended period in cold
weather, always check to be sure all wheels are rolling free
(brakes are not frozen) when starting out. Always clean
accumulated ice and snow from brake linkage.
148 3879634R1
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