light GMC C-SERIES 1999 User Guide

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2-18
The two-speed axle should be in low range when you
park the vehicle. Apply the parking brake, shift to
PARK (P) or NEUTRAL (N) and shut off the engine.
To operate off
-road or under a heavy load, shift into low
range when the vehicle is standing still and then operate
the transmission normally.
On the highway, with the axle in low range and
transmission in top gear, you may shift the axle to high
range by raising the switch and releasing the accelerator
momentarily. Re
-apply the accelerator after your shift.
Under light load conditions, first shift the axle into the
high range with the vehicle at a standstill and then
operate the transmission normally.
Manual Transmission
The switch for the rear axle
shift control is on the shift
lever. When the switch is
up, the rear axle is in the
high range. Push it down to
get the low range.
The two
-speed axle should be in low when you park the
vehicle. You'll need to engage the transmission, even
move the vehicle a little, to be sure the axle is in the low
range. Then apply the parking brake, shift into
NEUTRAL and shut off the engine.
Also, always start the vehicle in motion with the
two
-speed axle in the low range. When you upshift the
rear axle from low to high, move the switch up for the
high range, disengage the clutch, pause, engage the
clutch and then press down on the accelerator. When
you shift the axle down from high to low, you don't
have to clutch. Just move the switch down to low,
release the accelerator and then quickly apply it again.
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2-20
Air Suspension Dump Control (If Equipped)
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 on the upper left
side of the instrument panel
above the driver's side vent.
The light in the switch will be illuminated whenever the
switch is in the ªdumpedº position.
Automatic Transmission Operation
We build vehicles with four, five and six-speed
automatic transmissions. This part of the manual covers
the basics of these. With some of the transmissions, you
will find another manual in your vehicle that goes into
more detail. On the ceiling, in front of and above the
driver, or in some other place near the driver, you will
see a label that describes important operating facts about
the automatic transmission in your vehicle. Make sure
you follow the instructions on this label.
You may have a PARK (P) position for your shift lever.
This position locks your rear wheels. It is the best
position to use when you start your engine because your
vehicle can't move easily.
All vehicles equipped with automatic transmissions
can be started in PARK (P), if equipped, or in
NEUTRAL (N). When you shift out of NEUTRAL (N),
you may have to hold in a push button on the shift lever
or lift up on a release handle as you shift. See the
Allison Automatic Transmission Operator's Manual in
your vehicle for more information about this.
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2-24 Hydraulic Brakes
If your vehicle has hydraulic brakes, it has a parking
brake lever or an electric/hydraulic parking brake. The
lever is below the instrument panel to the left of the
steering column. The electric/hydraulic parking brake
knob is to the right of the steering column.
Your vehicle may also be equipped with an automatic
transmission which has a shift lever. This lever will have
a PARK (P) position on the shift indicator. When the
PARK (P) position is selected with the shift lever, the
parking brake is automatically applied.
Propshaft Brake Burnish Procedure
It is recommended that the propshaft-mounted parking
brake be burnished as part of the new vehicle break
-in.
The parking brake will work best after it has been
burnished following these instructions.
Make 10 stops, using the parking brake hand lever, from
20 mph (32 km/h) about 2 1/2 miles (4 km) apart.
Between stops, drive the vehicle at 20 mph (32 km/h).
Lever Operated Parking Brake
To apply the parking brake,
pull the lever all the way up.
The PARK BRAKE light
will come on when the
parking brake is applied.
Then shift the transmission
to NEUTRAL (N) or
PARK (P).
The vehicle must be stopped when applying the parking
brake, except while burnishing the parking brake linings
(see ªPropshaft Brake Burnish Procedureº in the Index).
You can easily adjust the parking brake by turning the
knob on the lever. Turning it clockwise makes the brake
grip more tightly. It will also make the lever seem harder
to pull up. Turning the knob counterclockwise makes the
parking brake apply less firmly. Adjust the parking
brake only when the lever is down (released).
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2-25
If your parking brake doesn't hold the vehicle when
applied, see your GM Truck dealer who can adjust your
parking brake properly.
To release the parking
brake, first push down the
regular brake pedal. Then,
push the parking brake lever
all the way down and shift
the automatic transmission
to NEUTRAL (N).
The PARK BRAKE light will remain illuminated if the
parking brake is not fully released.
NOTICE:
Driving with the parking brake on can overheat
the parts in the system. You may have to replace
them, and you could also damage other parts of
your vehicle.
Electric/Hydraulic Parking Brake
(If Equipped)
CAUTION:
It will take a few seconds for the parking brake
to fully apply, and even longer when it is cold
outside. Do not leave your vehicle until the
parking brake applies fully. Without the parking
brake applied, your vehicle is free to move. It
could hit someone or something.
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2-26
If your vehicle has this
system, you will have a
knob to the right of the
steering column.
To apply the parking brake, pull the knob toward you.
Then shift the transmission to NEUTRAL (N) or
PARK (P).
Push the knob in to release the parking brake. The
ignition must be in RUN and the shift lever out of
PARK (P) in order to release the parking brake.
The parking brake will automatically apply if the
ignition is turned off and in PARK (P) and will also
apply (will not release) if the vehicle's battery is dead
or disconnected.The PARK BRAKE light may flash while the parking
brake is being applied or released. This is normal for
this system.
If your vehicle needs towing or the parking brake will
not release, the towing operator will need to disconnect
the propshaft before towing your vehicle. See ªTowing
Your Vehicleº in the Index.
Air Brake (If Equipped)
CAUTION:
When the yellow SYSTEM PARK 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, either hold the regular brake
pedal down or, if you have it, pull out the blue
TRACTOR PARKING knob, to keep your rig
from moving.
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2-27
If your vehicle has air
brakes, you will have this
control. 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
one or two more air brake controls. They look like this:To charge a trailer's air brake system:
1. Move your tractor into the proper position. Apply the
parking brake by pulling the yellow SYSTEM PARK
knob out.
2. Hook up the trailer air system properly.
3. Get into the tractor. Push and hold down the regular
brake pedal.
4. Push in both the yellow SYSTEM PARK and the red
TRAILER AIR SUPPLY knobs. This will charge
your trailer's air system.
If you have the blue TRACTOR PARKING knob,
pull it out to set the tractor brakes while the air system
is charging.
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) and you may hear
the ªpop offº valve operate.
For driving with a trailer, the yellow, red and blue
(if equipped) knobs all 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 out.
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2-28
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 will come on. If
the air pressure drops to 40 to 45 psi (275 to 309 kPa), the
yellow knob will automatically pop out and apply the
spring brakes. 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.
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2-34
An arrow on the instrument panel will flash in the
direction of the turn when the lever is in the up or
down position.
This system replaces the turn signal feature of the
multifunction lever only. All other features such as
headlamp high/low beam, windshield wipers and
washer, etc. remain part of the multifunction system.
If you have this system, see ªSignal
-Stat Turn Signal
and Hazard Warning Flasherº in the Index to find out
how the hazard warning flasher portion works.
Headlamp High/Low Beam Changer
To change the headlamps from low beam to high, push
the multifunction lever away from you. To switch back
to low beam, pull the lever toward you.
When the high beams are
on, a light on the instrument
cluster will also be on.
Windshield Wipers
The windshield wipers are controlled by turning the
band with the wiper symbol on it.
For a single wiping cycle, turn the band to MIST. 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.
For steady wiping at low speed, turn the band away
from you to the LO position. For fast wiping, turn the
band to HI. To stop the wipers, turn the band to the
off symbol.
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2-35
Low Speed Delay Wipers (If Equipped)
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
choose the delay time.
The closer to LO, the
shorter the delay.
Heavy snow or ice can overload your wipers. Clear
away snow or ice to prevent bending or breaking the
wiper linkage.
Windshield Washer
At the top of the multifunction lever, there's a paddle
with the word PUSH on it. To spray washer fluid on the
windshield, push the paddle.
CAUTION:
In freezing weather, don't use your washer until
the windshield is warmed. Otherwise the washer
fluid can form ice on the windshield, blocking
your vision.
If you have the standard wipers, the wipers will keep
going in LO until you turn the wiper control to the
off symbol.
If you have the low
-speed delay option, the wipers will
clear the window and then either stop or return to your
preset speed.
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Using Cruise Control on Hills
How well your cruise control will work on hills depends
upon your speed, load and the steepness of the hills.
When going up steep hills, you may want to step on the
accelerator pedal to maintain your speed. When going
downhill, you may have to brake or shift to a lower gear
to keep your speed down. Of course, applying the brake
or clutch takes you out of cruise control. Many drivers
find this to be too much trouble and don't use cruise
control on steep hills.
Ending Cruise Control
There are different ways to turn off the cruise control:

Step lightly on the brake pedal.

Push the clutch pedal, if you have a
manual transmission.

Move the cruise switch to OFF.
Erasing Speed Memory
When you turn off the ignition, your cruise control set
speed memory is erased.Trailer Brake Hand Control Valve
(Option)
If your vehicle has this feature, it is mounted on the
steering column.
This control lets you apply the trailer brakes without
applying the tractor brakes. You can apply the trailer
brakes a little or apply them all the way if you have to.
Use this control only when you're driving. Don't use it
for parking or to hold the rig on a hill.
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