Page 111 of 386

2-36 Overdrive Defeat (If Equipped)
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 better fuel economy and fewer
downshifts while pulling a tractor or 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're starting to move the vehicle, it's 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's important not to increase the
engine speed sooner or before the clutch begins it's
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.
Page 112 of 386

2-37 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's 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 payload in the pickup box or
launching on a grade. Otherwise, start in SECOND (2)
gear. Only shift into FIRST (1) when the vehicle has
stopped moving.
Page 118 of 386
2-43
Vehicles built for use as tractors or towing vehicles have
two air brake controls. They look like this:To charge a trailer's air brake system do the following:
1. Move your tractor into the proper position.
2. Apply the parking brake by pulling the yellow
parking brake knob out.
3. Hook up the trailer air system properly.
4. Get into the tractor.
5. Push and hold down the regular brake pedal.
6. Push in both the yellow parking brake and the red
trailer air supply knobs. This will charge your
trailer's air system.
After a few minutes, the trailer system should be fully
charged. When it is, the air pressure gage will show
about 125 to 135 psi (862 to 931 kPa).
For driving with a trailer, the yellow and red
(if equipped) knobs must be pushed in. It's the same
when you're not pulling a trailer except that the red
trailer air supply knob must be pulled out.
Page 119 of 386

2-44
CAUTION:
If you apply any one of the air brake parking
controls while the vehicle is moving, your rig will
stop suddenly. If you are not ready for this, you
or others could be injured. Don't apply any one
of these controls while you're driving, unless you
have to make an emergency stop.
If the air pressure drops below 60 to 70 psi (413 to
482 kPa), the primary brake light and warning buzzer
will come on. If the air pressure drops to 35 to 45 psi
(241 to 310 kPa), the red trailer air supply knob will
automatically pop out and apply the spring brakes on
the trailer.If the air pressure drops to 35 to 45 psi (241 to 310 kPa),
the yellow park brake knob will automatically pop out
and apply the spring brakes on the truck or tractor.
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. See ªTowing Your Vehicleº in the Index.
CAUTION:
If your vehicle is left in gear, the engine can start
if the vehicle starts to roll. This can easily happen
if you have the diesel engine. Shift the
transmission into NEUTRAL (N) before you
leave the vehicle.
Page 124 of 386

2-49 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. See ªFuses and Circuit Breakersº in
the Index.
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. (See ªFuses and Circuit Breakersº
in the Index.)
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.
Page 125 of 386

2-50 Windshield Wipers
You control the windshield
wipers by turning the band
with the wiper symbol on it.
(Off): Turn the band on the lever to this symbol to
turn off the windshield wipers.
(Mist): For a single wiping cycle, turn the band to
this symbol. Hold it there until the wipers start, then let
go. The wipers will stop after one cycle. If you want
more cycles, hold the band on mist longer.
You can set the wiper speed for a long or short delay
between wipes. This can be very useful in light rain or
snow. Turn the band to one of the four delay settings to
choose the delay time. The further the band is turned
upward, the longer the delay will be. The further the
band is turned downward, the shorter the delay will be.
(Low Speed): For steady wiping at low speed,
turn the band toward you to the first solid band below
the delay settings.
(High Speed): For high-speed wiping, turn the
band further, to the second solid band below the delay
settings. To stop the wipers, move the band to off.
Be sure to clear ice and snow from the wiper blades
before using them. If they are frozen to the windshield,
carefully loosen or thaw them. If your blades do become
worn or damaged, get new blades or blade inserts. For
more information, see ªWindshield Wiper Blade
Replacementº in the Index.
Heavy snow or ice can overload your wipers. The
windshield wiper motor is protected from overload by a
circuit breaker and a fuse. If the motor overheats due to
heavy snow or ice the wiper will stop until the motor
cools. Although the circuit is protected from electrical
overload, overload due to heavy snow or ice may cause
wiper linkage damage. Always clear ice and heavy snow
from the windshield before using your windshield wipers.
Page 133 of 386

2-58
The exterior lamp control has four positions:
OFF: Turning the control to this position turns off all
lamps except the Daytime Running Lamps (DRL).
(Parking Lamps): Turning the control to this
position turns on the parking lamps, together with the
following:
Marker Lamps
Taillamps
License Plate Lamps
Instrument Panel Lights
(Headlamps): Turning the control to this position
turns on the headlamps, together with the previously
listed lamps and lights.
You can switch your headlamps from low to high
beam by pulling the turn signal/multifunction lever
toward you. Pull the lever toward you again to return
to low beam.
A circuit breaker protects your headlamps. If you have
an electrical overload, your headlamps will flicker on
and off. Have your headlamp wiring checked right away
if this ever happens.
Headlamps On Reminder (If Equipped)
If you have this system, a tone will sound when your
headlamps and/or parking lamps are turned on and your
ignition is in LOCK or ACCESSORY.
Daytime Running Lamps
Daytime Running Lamps (DRL) can make it easier for
others to see the front of your vehicle during the day.
DRL can be helpful in many different driving
conditions, but they can be especially helpful in the
short periods after dawn and before sunset. Fully
functional daytime running lamps are required on all
vehicles first sold in Canada.
The DRL system will make your headlamps come
on at reduced brightness when the following conditions
are met:
The ignition is on,
the exterior lamp control is off, and
the parking brake is released.
When the DRL are on, only your headlamps will be on.
The taillamps, sidemarker and other lamps won't be on.
Your instrument panel won't be lit up either.
Page 136 of 386
2-61 Illuminated Entry
The delayed illumination feature will allow you to enter
or exit your vehicle with the lights on for about 20
seconds, after the door is closed or the ignition is cycled.
Reading Lamps (If Equipped)
If your vehicle has reading lamps, press the button next
to the lamp to turn the lamp on or off.
Mirrors
Inside Rearview Mirror (If Equipped)
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 Rearview 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. Some
mirrors can be folded in to enter narrow passageways.