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Overdrive Defeat
If your vehicle has this feature, you can select not to
shift up to fifth gear. This is useful when towing or under
a heavy load.
The overdrive defeat
switch is located in the
instrument panel to
the right of the
steering column.
Press the switch to limit the transmission to fourth gear.
This will allow for fewer downshifts while pulling a
trailer or under a heavy load. The indicator light in the
switch will come on whenever overdrive defeat is active.
Manual Transmission Operation
Using the Clutch
When you are starting to move the vehicle, it is
important to begin with the engine speed at idle.
Then start to engage the clutch and listen for an engine
speed drop of about 100 rpm. At this point, the clutch
is engaging, so you should increase the engine speed
and fully engage the clutch. It is important not to
increase the engine speed sooner or before the clutch
begins its engagement. If you do, you can cause
damage to your vehicle.
Double-Clutching
You must use the double-clutching method when you
shift an unsynchronized gear set. Disengage the clutch,
shift to NEUTRAL and engage the clutch. When
upshifting, slow the engine until the engine rpm and
road speed match. When downshifting, accelerate the
engine until the engine rpm and road speed match.
Then quickly disengage the clutch and move the shift
lever to the next gear position and engage the clutch.
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Eaton®Fuller®Five and Six-Speed
Transmissions and TTC Spicer
Seven-Speed Transmissions
These transmissions have gears that automatically
synchronize when you shift up or down (except
FIRST (1) gear on the five-speed and seven-speed
transmission which is unsynchronized). Choose the
gear that will maintain the road speed you want while
keeping the engine above two-thirds of the governed
speed. When the engine speed drops below two-thirds
of the governed speed, shift into the next lower gear
before your engine begins to lug. When you shift down,
be sure to double-clutch if required.
ZF Six-Speed Transmission
Here is how to operate your transmission.
This six-speed pattern is
unique to GM manual
transmissions.
The transmission always repositions the shift lever to
NEUTRAL, which is located between FOURTH (4)
and FIFTH (5) gear.
To prevent unintentional gear selections, additional force
is required to move the shift lever into REVERSE (R) or
FIRST (1). Use FIRST (1) when trailer towing, driving
with a heavier payload or launching on a grade.
Otherwise, start in SECOND (2) gear. Only shift into
FIRST (1) when the vehicle has stopped moving.
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Page 100 of 374

Electronic Transfer Case
If your vehicle is equipped
with four-wheel drive, the
transfer case knob is
located to the right of the
steering wheel on the
instrument panel. Use this
knob to shift into and
out of four-wheel drive.
Recommended Transfer Case Settings
Driving ConditionsTransfer Case Settings
2m4m4nN
Normal YES
Severe YES
Extreme YES
Vehicle in Tow* YES
*SeeTowing Your Vehicle on page 4-35for further
information.An indicator light will show you which position the
transfer case is in. The indicator lights will come on
briefly when you turn on the ignition and one will stay on.
If the lights do not come on, you should take your
vehicle to your dealer for service. An indicator light will
flash while shifting the transfer case. It will remain
illuminated when the shift is complete. If for some
reason the transfer case cannot make a requested shift,
it will return to the last chosen setting.
2
m(Two-Wheel High):This setting is for driving in
most street and highway situations. The transfer
case does not drive the front axle in two-wheel drive.
The front-axle will spin if the front wheel hubs are
locked. Be sure to unlock the hubs to achieve the best
fuel economy.
4
m(Four-Wheel High):Use Four-Wheel High when
you need extra traction, such as on snowy or icy roads or
in most off-road situations. Be sure the front wheel hubs
are locked when you want to drive in Four-Wheel High.
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4n(Four-Wheel Low):This setting sends maximum
power to all four wheels. You might choose Four-Wheel
Low if you are driving off-road in deep sand, deep mud,
and climbing or descending steep hills. Be sure the
front wheel hubs are locked when you want to drive in
Four-Wheel Low.
{CAUTION:
Shifting the transfer case to NEUTRAL can
cause your vehicle to roll even if the
transmission is in PARK (P). You or someone
else could be injured. If you are going to leave
your vehicle, set the parking brake and shift
the transmission to PARK (P) and make sure
the transfer case is in a drive gear.Notice:If your vehicle has an Allison
®transmission
and you try to put the transmission in PARK (P)
while the transfer case is in Four-Wheel Low,
the transmission may not go into PARK (P) and
could damage your vehicle. When parking your
vehicle, make sure the transfer case is in Two-Wheel
High or Four-Wheel High.
NEUTRAL:Shift the vehicle’s transfer case to
NEUTRAL only when towing your vehicle.
Shifting Into Four-Wheel High
Turn the knob to four-wheel high. This can be done
at 3 mph or less and when you are shifting out of
Four-Wheel Low. The indicator light will flash while
shifting. It will remain illuminated when the shift is
complete.
Shifting Into Two-Wheel High
Turn the knob to Two-Wheel High. This can be done
at 3 mph or less and when you are shifting out of
Four-Wheel Low.
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Page 106 of 374
Air Brake
If your vehicle has air
brakes, you will have
this parking brake.
It is located above
the radio in the
instrument panel.
Pulling it out applies the parking brake. The park brake
light will come on when the air parking brake is applied.Vehicles built for use as tractors or towing vehicles have
two air brake controls. They look like this:
{CAUTION:
When the yellow PARKING BRAKE and the red
TRAILER AIR SUPPLY knobs are both pushed
in, your rig will be free to move. It could strike
someone or something. When both of these
knobs are pushed in, hold the regular brake
pedal down to keep your rig from moving.
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If you ever have a complete loss of air so that your air
brakes automatically apply, there is a way that the
tow operator can release the parking brakes to tow the
vehicle. SeeTowing Your Vehicle on page 4-35.
Air Suspension
Your vehicle may have the Hendrickson HAS Series
single-axle air suspension which is designed for a
single-axle on-highway use. This feature is available in
19,000 lb (8 613.3 kg), 21,000 lb (9 525.4 kg) and
23,000 lb (10 432.6 kg) capacities.
Rear Air Suspension Dump Control
If your vehicle is equipped with the Hendrickson HAS
Series single-axle air suspension, you may have
this control. The air suspension dump control allows the
operator to lower the deck height approximately
4.5 inches (11.5 cm) from the normal frame height.
The switch to deflate and
inflate the air suspension
is located in the instrument
panel.
Press the bottom of the switch to deflate the air
suspension and lower the deck height. Press the
top of the switch to return the suspension to normal
deck height.
An indicator light will come on and stay on whenever
the switch is in the dumped position.
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Page 111 of 374
Mirrors
Manual Rearview Mirror
If your vehicle has this feature, pull the tab under the
mirror toward you to reduce glare from headlamps
behind you after dark. Push the tab away from you to
restore the mirror to the daytime position.
Outside Manual Mirrors
Adjust the outside rearview mirrors so you can see a
little of the side of your vehicle, and the area beside your
vehicle from a comfortable driving position. All mirrors
can be folded in to enter narrow passageways.
Outside Power Mirrors
If you have outside power mirrors, they can be adjusted
from the inside of the vehicle.
The control for this
feature is located on the
driver’s door.
Select the mirror you want to move by turning the
switch clockwise to adjust the passenger’s side mirror,
or counterclockwise to adjust the driver’s side mirror.
The center position is neutral.
Then, adjust the mirror by pressing the outer arrows on
the switch until the mirror is in the desired position.
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Page 122 of 374

Turn and Lane-Change Signals
The turn signal has two upward (for right) and
two downward (for left) positions. These positions
allow you to signal a turn or a lane change.
To signal a turn, move the lever all the way up or
down. When the turn is finished, the lever will
return automatically.
An arrow on the instrument
panel cluster will flash in
the direction of the
turn or lane change.
To signal a lane change, just raise or lower the lever
until the arrow starts to flash. Hold it there until you
complete your lane change. The lever will return by itself
when you release it.As you signal a turn or a lane change, if the arrows
don’t flash but just stay on, check the turn signal flasher
and circuit breaker. SeeFuses and Circuit Breakers
on page 5-89.
If a bulb is burned out, replace it to help avoid an
accident. If the arrows don’t go on at all when you
signal a turn, check the circuit breaker and for
burned-out bulbs.
Headlamp High/Low-Beam Changer
To change the headlamps from low to high beam or
high to low beam, pull the multifunction lever all the way
toward you, then release it.
When the high beams are
on, this light on the
instrument panel cluster
will also be on.
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