It is not recommended, or approved, for axle conversions to be
performed. However, it is understood that, on occasion, aftermarket
add-on axles are installed by others on the truck chassis which allow
operator control for weight transfer from other axles (i.e., air lift axles).
TWO-SPEED REAR AXLE (IF EQUIPPED)
WARNING:Never shift a two-speed axle when descending a
steep grade as this may cause loss of vehicle control and result in
personal injury.
Note:Do not shift between ranges when the speed control is on.
A two-speed rear axle allows the
driver to select a low range for
greater pulling power and a high
range for greater road speed and
fuel economy. These ranges can also
be used to provide additional steps
between transmission shifts when
driving on steep grades or fuel
economy may be factors.
Axle Shifting with a Manual Transmission
To downshift, select the next lower gear, release and press the
accelerator pedal rapidly, or while holding the accelerator pedal down,
release and engage the clutch rapidly.Note:The clutch method is
recommended when driving at slower speeds.
To upshift, keep the accelerator pedal down, select the next higher gear,
release the accelerator and pause until the axle upshifts.Note:
De-clutch for smoother axle upshifts when driving at slower speeds.
Axle Shifting with an Automatic Transmission
Note:You cannot split-shift with an automatic transmission. Also,
downshifting above 40 mph (64 km/h) may result in transmission or axle
damage.
Note:Do not shift the axle to LOW with the vehicle in motion.
Use LOW when you drive a fully-loaded vehicle on a severe grade or in
congested traffic. Press the upper portion of the switch.
Use HIGH for all normal driving conditions with a lightly-loaded or
partially-loaded vehicle. Press the lower portion of the switch.
2SPD
LOW
HIGH
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To shift the axle from LOW to HIGH with the vehicle stopped, place the
transmission in positionN,then press the lower part of the switch.
To shift the axle from LOW to HIGH with the vehicle moving, accelerate
to approximately 35 mph (56 km/h), press the lower part of the switch
while the transmission is in positionN,then release and apply the
accelerator.
To shift the axle from HIGH to LOW with the vehicle stopped, place the
transmission in positionN,then press the upper part of the switch.
Split-shifting (Combined Axle and Transmission Shift)
(Manual Transmission Only)
To downshift the axle to a slower ratio and shift the transmission, shift
the transmission and move the switch to the lower ratio before the
clutch is re-engaged.
To upshift the axle and shift the transmission, move the switch to a
faster ratio and make the transmission shift in the usual manner.
Split-shift Sequence
Ratio combination1234567891011
Transmission gear 1st 1st
2nd 2nd3rd 3rd 4th 4th 5th 6th 6th
Axle range LO HI LO HI LO HI LO HI LO LO HI
Ratio Extender Use
Low end:A two-speed axle can be used as a ratio-extender when
split-shifting is not necessary. For low end use, just shift the axle into
LOW to start out, and shift to HIGH when the extra torque is no longer
needed.
Transmission (5-speed) 1st 1st 2nd 3rd 4th 5th 6th
Two-speed axle Axle low Axle high
High end:To use the two-speed axle as a high end ratio-extender, stay
in the LOW range for normal upshifts and only shift the axle to HIGH on
the freeway for greater road speed.
Transmission (5-speed) 1st 2nd 3rd 4th 5th 6th
Two-speed axle Low for gradeability Axle high
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HINTS ON DRIVING WITH ANTI-LOCK BRAKES
When the system is operating, the brake pedal pulses and may travel
further. Maintain pressure on the brake pedal. You may also hear a noise
from the system. This is normal.
The ABS does not eliminate the dangers inherent when:
•You drive too closely to the vehicle in front of you.
•Your vehicle is hydroplaning.
•You take corners too fast.
•The road surface is poor.
EXHAUST BRAKE (IF EQUIPPED)
WARNING:The exhaust brake is not recommended for use on
slippery or low traction road surfaces. Under these conditions a
loss of vehicle control could occur.
Note:Installing an exhaust or auxiliary brake does not necessarily
protect the engine from exceeding maximum governed speed. The
primary brakes should be used to make sure the engine never exceeds
maximum governed speed under any conditions.
Note:Before starting the engine, make sure that the exhaust brake
switch is pushed down to the off position. Do not turn the exhaust brake
on until the engine has reached normal operating temperature.
Note:Maximum exhaust brake performance is related to the type of
transmission your vehicle is equipped with.
Note:Engine speed has a major influence of retarding performance.
When engine speed is maintained at the maximum allowable level, the
exhaust brake operates at peak performance.
Note:Manual transmissions should be downshifted to the lowest gear
possible, without exceeding the maximum RPM limit of the engine.
This maximizes the exhaust brake’s retarding effect.
Note:Exhaust brakes operate effectively with automatic transmissions,
but performance varies with engine speed and the gear selected by the
transmission.
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An exhaust brake is an auxiliary braking system that assists, but does
not replace, the primary service brake system. It is intended to help
control vehicle speed. It is not a vehicle stopping device.
A switch on the instrument panel,
in combination with the accelerator
and clutch pedal, allows the
operator to make maximum use of
the exhaust brake in the following
conditions:
•off-highway driving
•mountain driving
•heavy traffic
•high-speed highway driving.
To operate the brake, push the switch up to turn it on. Push the switch
down to turn it off.
While approaching a steep grade, make sure that the exhaust brake
switch is in the on position. The exhaust brake begins working as soon as
you remove your foot from the accelerator pedal.
Before descending a hill or steep grade, always select the proper gear. If
the transmission is taken out of gear while descending, it is possible that
you cannot select another gear because of maximum RPM being
governed.
Make sure the engine speed does not exceed the maximum allowable
engine RPM. Exceeding the maximum allowable engine RPM can result
in damage to the engine. Apply the service brakes to reduce the engine
RPM or make a slower descent by using a lower gear.
While going down the grade, use a low enough gear to descend safely
with a minimum application of the service brakes. As a general guideline,
use the same gear as you use to ascend the hill.
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PARKING BRAKE
Hydraulic Brakes
WARNING:Do not use the gearshift selector in place of the
parking brake. Always set the parking brake fully AND make sure
the gearshift selector is in positionRfor vehicles equipped with a
manual transmission or positionP (if equipped)orNfor vehicles
equipped with an automatic transmission. Use of wheel chocks is also
recommended in hilly or off-road usage. Unexpected and possible
sudden vehicle movement may occur if these precautions are not taken.
WARNING:If the parking brake is fully released but the parking
brake warning lamp remains illuminated, the brakes may not be
working properly. See your dealer or a qualified service technician.
Apply the parking brake whenever the vehicle is parked. To set the
parking brake, pull the handle up until it snaps into the locked position.
When the parking brake is out of adjustment, seek service immediately.
The parking brake warning lamp in the instrument cluster
illuminates, and remains illuminated (when the ignition is
turned on), until the parking brake is released.
Push the palm release lever (A) on
the parking brake handle (B) and
push down as far as possible to
release the brake. Driving with the
parking brake on causes the brakes
to wear out quickly and reduces
fuel economy.
The parking brake is not recommended to stop a moving vehicle.
However, if the normal brakes fail, the parking brake can be used to stop
your vehicle in an emergency. Since the parking brake only applies
retardation to the rear wheels, the vehicle’s stopping distance increases
greatly and the handling of your vehicle is adversely affected.
Power Park (Hydraulic Brake Vehicles Only)
This feature uses a brake chamber mounted on the chassis to power a
spring-applied, hydraulically-released driveline parking brake.
P
A
B
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The Power Park Brake is controlled by the park brake dash-mounted,
yellow knob-type switch. The switch has three positions: apply (out),
neutral (central), and release (in). The switch is spring-loaded to return
to the neutral (central) position after being pushed or pulled.
There is no visual indication at the knob that the park brake is
applied or released; check the instrument cluster. If the light is
illuminated, the parking brake is applied.
Applying the Parking Brake
Pull the yellow, dash-mounted parking brake knob. The parking brake
light illuminates indicating that the parking brake has been successfully
set.
Note:If the light blinks and a warning chime sounds when the control
knob is pulled, the parking brake is not functioning properly. Seek
immediate service from your dealer. SeeParking brake warning
systemin this section.
Releasing the Parking Brake
WARNING:Hold the brake pedal down while moving the
gearshift lever from position to position. If the brake pedal is not
held down, the vehicle may move unexpectedly resulting in property
damage, personal injury or death.
Note:Read and understand the following steps and perform them
whenever you prepare to drive the vehicle.
Note:The parking brake does not disengage unless sufficient system air
pressure is available.
If your vehicle is equipped with a dash-mounted push button (Allison
3000 Series) or steering column-mounted (Allison 2200 and 2500) gear
selector:
1. Press and hold the service brake pedal while the engine is running.
2. Select the appropriate drive gear.
3. Push and hold the yellow, dash-mounted parking brake knob until the
parking brake light turns off, then release.
If your vehicle is equipped with a manual transmission:
1. Press and hold the service brake pedal while the engine is running.
2. Press and hold the clutch pedal.
3. Select the appropriate drive gear.
4. Push and hold the yellow, dash-mounted parking brake knob until the
parking brake light turns off, then release.
P
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Loosen the jam nut (A) and un-thread the adjustment rod (B) from the
chamber to reduce tension on the cable (C). Continue to un-thread the
adjustment rod all the way and remove it from the chamber. The nut and
shaft are metric.
Air Brakes
WARNING:Do not use the gearshift selector in place of the
parking brake; unexpected and possible sudden vehicle
movement may occur if these precautions are not taken. Always set the
parking brake fully AND make sure the gearshift selector is in position
Rfor vehicles equipped with manual transmission or positionN(except
Allison 2200 transmission) orP(Allison 2200 transmission) for vehicles
with automatic transmission.
If the service brakes should fail to operate while the vehicle is in motion,
you can make an emergency stop with the parking brake. Since the
parking brake only applies stopping power to the rear wheels, the
vehicle’s stopping distance greatly increases and the handling of the
vehicle is adversely affected. Repairs should be made immediately to an
inoperative air brake system circuit.
WARNING:This control is used for parking only. Do not leave
the vehicle unattended after setting the parking brake without
placing the transmission inpositionRfor vehicles equipped with manual
transmission or positionN(except Allison 2200 transmission) orP
(Allison 2200 transmission) for vehicles with automatic transmission.
Use of wheel chocks is also recommended in hilly or off-road usage.
CA
B
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OPERATING YOUR VEHICLE
General Information
•Start the vehicle in motion by using the highest gear speed in the
transmission that lets the engine easily start the load without slipping
the clutch.
•Accelerate smoothly and evenly. Rapid acceleration increases fuel
consumption without increasing engine performance.
•When approaching a hill, press the accelerator smoothly to start the
incline at full power, then shift down as needed to maintain vehicle
speed.
•When going down a hill, or long steep grades, prevent overspeeding
of the engine. Normally, choose the same gear to descend the hill that
you use to ascend the hill. The engine governor has no control over
engine speed when it is being pushed by a loaded vehicle.
•Operate in a gear that permits an engine speed not in excess of the
maximum governed speed or high-idle RPM (no load).
•
Always shift to a lower gear at high altitudes to prevent engine smoking.
Backing Up
WARNING:All vehicles have blind spots. To reduce the risk of
severe injury or property damage, never move your vehicle to the
side or rear or change lanes without being sure your way is clear on
both sides and to your rear.
WARNING:To reduce the risk of the possibility of personal
injury while backing up the vehicle, always be sure your vehicle’s
path is clear.
Before backing up your vehicle, be sure you can do so safely. If anything
behind the cab limits your view, do not rely on mirrors alone to ensure
that your intended path is clear. If other people are in the vicinity, have
someone standing well behind your vehicle and outside of your intended
path (visible through an exterior mirror) guide you as you back up.
Although OSHA or some governmental regulations may require the use
of an electrical or mechanical back up alarm to warn bystanders, such an
alarm does not guarantee that the intended path is clear. When in doubt,
get out of the vehicle and visually check the intended path is clear. Back
up slowly as to allow others time to move, if necessary.
If an electrical back up alarm is installed, it should be connected to the
back up lamp circuit.
168Driving Aids
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USA(fus)