The engine idle speed will return to normal once the
following conditions are met:
•Once engine coolant temperature reaches about
150°F (65°C).
•The intake temperature reaches a certain level.
The high idle speed will be temporarily interrupted and
the engine speed will return to normal if any of the
following conditions occur:
•The brake pedal is applied.
•The accelerator pedal is pressed.
•The automatic transmission is shifted out of
PARK (P) or NEUTRAL (N).
•The clutch pedal on the manual transmission is
pressed.
•Vehicle speed is detected.
Once these conditions no longer exist, the engine idle
speed will slowly increase to high idle after the
normal delay, if the conditions for engine coolant
temperature and air intake temperature are still met.
Engine Checks Before Operating
When you have started your engine, let it run for
20 to 30 seconds before you put a load on the
engine. But do not leave the vehicle while the engine
is running.
Avoid unnecessary idling of diesel engine equipped
vehicles.
If the engine idles too long, the temperature of the
engine coolant will fall below the normal operating
range. Low engine operating temperature causes
several conditions which affect engine operation and
reduce engine life.
The engine should be permitted to go through a
warm-up period. Operate the vehicle at a minimum of
600 rpm during the warm-up period. During this
period and during operation, the following observations
should be made.
2-23
During this warm-up period, check your warning lights
and gages:
•If oil pressure does not begin to rise within
15 seconds of starting, stop the engine and find the
cause. SeeOil Pressure Gage on page 3-37for
more information.
•If the engine coolant temperature gage needle goes
into the hot area on the gage, stop the engine and
find the cause of the overheating. SeeEngine
Coolant Temperature Gage on page 3-35for more
information.
•If you have air brakes, the dual-needle air pressure
gage should read at least 115 psi (790 kPa) for both
service systems before you try to move the vehicle.
When air pressure is below 60 psi (420 kPa), the
LOW AIR light will come on and you will hear a tone
alarm. SeeBrake System Warning Light on
page 3-32for more information. If the pressure does
not build up or drops during warm-up, stop the
engine and find the cause before you try to move the
vehicle. Recommended air pressure before driving is
120 psi (830 kPa). SeeAir Pressure Gage on
page 3-46for more information.
•The charging system light should come on when the
ignition key is turned to ON/RUN or START and
should go out when the engine is running above idle.
If the light does not go out or comes back on during
normal engine operation, have the charging system
checked right away. (This light tells you if the
generator is not charging; it does not reflect the
condition of the battery.) SeeCharging System Light
on page 3-30for more information.
•The voltmeter charge indicator gage tells you the
condition of your battery’s charge. The gage should
be in the center area during engine operation. The
red area on the left indicates an undercharge
condition; the red area on the right indicates an
overcharge. If the gage is in either red area, have the
battery and charging system checked right away.
SeeVoltmeter Gage on page 3-31for more
information.
Notice:Do not allow the engine to operate at low
idle for more than ve minutes. This can cause
low engine operating temperatures which can affect
engine operation and reduce engine life. Engine
idle speed should be increased to 1200 rpm
whenever extended idle is required. Once started,
the engine should be placed under load to allow the
engine coolant temperature to reach 150°F (66°C)
before shutting off the engine.
2-24
Diesel Engine Exhaust Brake
If your vehicle has a Isuzu 6H Diesel Engine, it may
have an exhaust brake, which is located in the exhaust
system.
If your vehicle has a 6.6L DURAMAX
®6600 or
Caterpillar®Diesel Engine, it may have an exhaust
brake, which is controlled through the turbocharger.
The exhaust brake for both engines operates the same.
The exhaust brake switch
is located in the instrument
panel switchbank.
Push the bottom of the switch to turn the exhaust brake
on. When you push the top of the switch, the exhaust
brake will turn off.
There is an indicator light on the instrument panel
similar to the symbol on the switch, that comes on when
the exhaust brake is active. SeeExhaust Brake
Indicator Light on page 3-40for more information.While using the exhaust brake, the proper gear range
selection is important. The exhaust brake is most
effective if the gear range selected is the lowest possible
range that does not allow the engine rpm to go more
than 200 rpm above rated (full load) rpm. If you have a
Caterpillar
®Diesel Engine, do not exceed 2900 rpm.
If you have an Isuzu 6H Diesel engine, do not exceed
2550 rpm. If your vehicle has a DURAMAX
®6600
Diesel Engine, do not exceed 3600 rpm.
If your vehicle has an Allison
®1000/2200/2300/
2350/2500/2550 series automatic transmission and this
button is pressed, the transmission downshifts to a
factory default setting of third gear. To change
the default setting, or for more information on factory
default settings, contact your dealer/retailer for
assistance.
The accelerator and clutch pedals must be released in
order for the exhaust brake to engage. The exhaust
brake will automatically shut off when the antilock brake
system is active.
If your vehicle has a Caterpillar
®Diesel Engine or a
DURAMAX®6600 Diesel Engine, the exhaust brake will
become active in cruise control when you exceed the
set speed by 3 to 5 mph.
2-26
Automatic Transmission Operation
Your vehicle has either an Allison®five-speed or
six-speed automatic transmission. This part of the
manual covers the basics of these. With these
transmissions, you will find another Allison
®manual in
your vehicle that goes into more detail. On the headliner,
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.
Be sure to keep your parking brake set until you are
ready to shift into DRIVE (D). SeeParking Brake (With
Hydraulic Brakes) on page 2-38orParking Brake
(With Air Brakes) on page 2-41for parking brake
procedure. Press the brake pedal while shifting from
NEUTRAL (N) or PARK (P) to a drive gear.
All vehicles that have an with automatic transmission
can be started in PARK (P), if equipped, or in
NEUTRAL (N). See the Allison
®Transmission
Operator’s Manual in your vehicle for more information
about this.
{CAUTION:
It can be dangerous to get out of your vehicle
without the parking brake rmly set. Your
vehicle can roll. If you have left the engine
running, the vehicle can move suddenly. You or
others could be injured. To be sure your vehicle
will not move, even when you are on fairly level
ground, always set the parking brake.
{CAUTION:
Shifting into a drive gear while the engine is
running at high speed is dangerous. Unless
your foot is rmly on the brake pedal, your
vehicle could move very rapidly. You could
lose control and hit people or objects. Do not
shift into a drive gear while your engine is
running at high speed.
2-29
Eaton®Fuller®Nine and Ten-Speed
Non-Synchronized Manual
Transmissions
If your vehicle has one of these transmissions the
engine rpm and road speed must match when upshifting
and downshifting. The label above the windshield will
tell you the operating basics you need to know.
The following are driving tips.
•Always choose an initial starting gear suitable for
the load and terrain.
•Always use double-clutching procedures when
shifting.
•Never move the range shift lever to the LO speed
gear position after HI range preselection, or
anytime the transmission is in the HI range.
•Never move the range knob or lever with the shift
lever in NEUTRAL while the vehicle is moving.
•Never make a range shift while moving in
REVERSE (R).
Clutch Brake (Vehicles with
Non-Synchronized Transmission)
A clutch brake is used to stop transmission input shaft
rotation so that FIRST (1) or REVERSE (R) gear
selection can be initiated when the vehicle is at a
standstill and the engine is idling.
Press the clutch pedal all the way down to the floorboard
to apply the clutch brake.
When using the clutch brake, disengage the clutch
pedal and shift the transmission into either the initial
starting gear or REVERSE (R). If the tooth-butting
occurs between the clutching teeth, re-engage the clutch
while applying light pressure to the shift lever. This
will provide for a smooth shift into either FIRST (1) or
REVERSE (R) gear.
Notice:Using the clutch brake for shifting into any
gear other than FIRST (1) or REVERSE (R) may
cause premature wear of the clutch brake and make
gear shift effort more difficult. Do not use the
clutch brake for shifting after engaging FIRST (1) or
REVERSE (R).
2-31
Recommended Transfer Case Settings
Driving ConditionsTransfer Case Settings
2m4m4nN
Normal YES
Severe YES
Extreme YES
Vehicle in Tow* YES
*SeeTowing Your Vehicle on page 4-24for further
information.
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 spins 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.
4
n(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.
2-34
Shifting Out of Four-Wheel Low
To shift from Four-Wheel Low to Four-Wheel High or
Two-Wheel High, your vehicle must be stopped or
moving less than 3 mph (5 km/h) with the transmission in
NEUTRAL (N) and the engine running. The preferred
method for shifting out of Four-Wheel Low is to have your
vehicle moving 1 or 2 mph (1.6 to 3.2 km/h). Turn the
knob to Four-Wheel High or Two-Wheel High. You must
wait for the Four-Wheel High or Two-Wheel High
indicator light to stop flashing and remain on before
shifting the transmission into gear.
Notice:Shifting the transmission into gear before
the Four-Wheel High or Two-Wheel High indicator
light has stopped ashing could damage the transfer
case. To help avoid damaging your vehicle, always
wait for the Four-Wheel High or Two-Wheel High
indicator light to stop ashing before shifting
the transmission into gear.
If the knob is turned to Four-Wheel High or Two-Wheel
High while your vehicle is in gear and/or moving, the
Four-Wheel High or Two-Wheel high indicator light
flashes for 30 seconds. It will not complete the shift
unless your vehicle is moving less than 3 mph (5 km/h)
with the transmission in NEUTRAL (N).
Shifting Into NEUTRAL
Before shifting the transfer case to NEUTRAL, first
make sure the vehicle is parked so that it will not roll.
1. Set the parking brake. SeeParking Brake (With
Hydraulic Brakes) on page 2-38orParking Brake
(With Air Brakes) on page 2-41for parking
brake apply procedure.
2. Start the vehicle.
3. Put the transmission in NEUTRAL (N).
4. Shift the transfer case to Two-Wheel High.
5. Turn the transfer case knob all of the way past
Four-Wheel Low and hold it there for a minimum of
10 seconds. The NEUTRAL indicator light comes on.
6. Shift the transmission to REVERSE (R) for
one second, then shift the transmission to
DRIVE (D) for one second.
7. Turn the ignition to OFF.
8. Place the transmission shift lever in PARK (P).
9. Turn the ignition to LOCK.
2-36
Shifting Out of NEUTRAL
To shift the transfer case out of NEUTRAL, do the
following:
1. Set the parking brake. SeeParking Brake (With
Hydraulic Brakes) on page 2-38orParking Brake
(With Air Brakes) on page 2-41for parking
brake apply procedure.
2. Apply the regular brake pedal.
3. Turn the ignition to ON/RUN with the engine off.
4. Put the transmission in NEUTRAL (N).
5. Turn the transfer case knob to the desired shift
position (Two-Wheel High, Four-Wheel High,
Four-Wheel Low).
6. After the transfer case has shifted out of NEUTRAL,
the indicator light goes out.
Notice:Driving with the parking brake on can
overheat the brake system and cause premature
wear or damage to brake system parts. Verify that
the parking brake is fully released and the brake
warning light is off before driving.7. Release the parking brake.
8. Start the engine and shift the transmission lever to
the desired position.
Excessively shifting the transfer case into or out of the
different modes can cause the transfer case to enter the
shift protection mode. This protects the transfer case from
possible damage and only allows the transfer case to
respond to one shift per 10 seconds. The transfer case
can stay in this mode for up to three minutes.
Parking
{CAUTION:
If you do not park your vehicle properly, it can
roll. If you have left the engine running, it can
move very quickly. You or others could be
injured. To be sure your vehicle will not move,
even when you are on level ground, follow the
steps below.
2-37