2008 HUMMER H3 brake

For mounds, washouts, loose up-hill
slopes, ditches, etc.
When wheel spin occurs as the vehicle is moving, the
driver may notice a slight shaking or shuddering of
the vehicle. This should be stopped as soon as possible
to prevent damage to vehicle components. This is the
indication that a loss of traction is occurring on this
terrain. The operator should:
1. Reduce speed and apply the brakes.
2. Assess the terrain properly and adjust
vehicle speed and gear ranges accordingly:
Four-Wheel High position for higher speeds and
Four-Wheel-Low Lock for more torque and
lower speeds. Transmission FIRST (1) gear is
generally recommended.
3. Apply slight pressure to the brake when the
shaking or shuddering sensation is felt, keeping
the vehicle moving in a controlled manner.
4. Be prepared to alternate between braking and
accelerating through the adverse terrain.
Getting Familiar with Off-Road Driving
It is a good idea to practice in an area that is safe
and close to home before you go into the wilderness.
Off-road driving does require some new and different
skills. Here is what we mean.
Tune your senses to different kinds of signals. Your
eyes, for example, need to constantly sweep the terrain
for unexpected obstacles. Your ears need to listen
for unusual tire or engine sounds. With your arms,
hands, feet, and body, you will need to respond to
vibrations and vehicle bounce.
Controlling your vehicle is the key to successful off-road
driving. One of the best ways to control your vehicle
is to control your speed. Here are some things to keep
in mind. At higher speeds:
You approach things faster and you have less time
to scan the terrain for obstacles.
You have less time to react.
You have more vehicle bounce when you drive
over obstacles.
You will need more distance for braking, especially
since you are on an unpaved surface.
4-18

Because you will be on an unpaved surface, it is
especially important to avoid sudden acceleration,
sudden turns, or sudden braking.
In a way, off-road driving requires a different kind of
alertness from driving on paved roads and highways.
There are no road signs, posted speed limits, or signal
lights. You have to use your own good judgment
about what is safe and what is not.
Drinking and driving can be very dangerous on any
road. And this is certainly true for off-road driving.
At the very time you need special alertness and
driving skills, your reexes, perceptions, and judgment
can be affected by even a small amount of alcohol.
You could have a serious — or even fatal — accident
if you drink and drive or ride with a driver who has
been drinking. SeeDrunk Driving on page 4-2.Crossing Obstacles
Approach Angle — a Key to Mobility
If you encounter a large dip in the terrain, do not enter
straight on; enter at an angle — 15 degrees minimum
approach (A), 75 degrees maximum approach angle (B).
For very large dips, ditches, or small washes, coast
in, using the engine as a brake (transmission and
transfer case lowest gears). Then, use the low ranges
in the transmission and transfer case to power out.
4-20

Roll Your Tires Over Large Rocks
Do not straddle large
rocks; drive over them,
letting the tire cover
the rock. The tread of
the tire is thicker and
tougher than the
sidewall of the tire and
is more resilient to
impact than underbody
components.
Log Crossing
Using the proper technique, your vehicle will cross
logs up to 10 inches (25.4 cm) in diameter. Approach
the log at approximately a 15 degree angle (A) with
the transmission in FIRST (1) and the transfer case in
Four-Wheel-Low Lock and “walk” your vehicle over,
one tire at a time. It may be necessary to modulate
your brake pedal and accelerator to avoid spin-out.
Ease the vehicle down from the log with your brake.
4-21

Sound the horn as you approach the top of the
hill to let opposing traffic know you are there.
Use your headlamps even during the day.
They make your vehicle more visible to
oncoming traffic.
{CAUTION:
Driving to the top (crest) of a hill at full speed
can cause an accident. There could be a
drop-off, embankment, cliff, or even another
vehicle. You could be seriously injured or
killed. As you near the top of a hill, slow down
and stay alert.There are some things you should do if the vehicle stalls,
or is about to stall, and you cannot make it up the hill:
Push the brake pedal to stop the vehicle and keep
it from rolling backwards. Also, apply the parking
brake.
If your engine is still running, shift the transmission to
REVERSE (R), release the parking brake, and slowly
back down the hill in REVERSE (R).
If your engine has stopped running, you will need
to restart it. With the brake pedal pressed, apply
the parking brake. If you have an automatic
transmission, shift the transmission to PARK (P).
Restart the engine. Then, shift to REVERSE (R),
release the parking brake, and slowly back down
the hill as straight as possible in REVERSE (R).
As you are backing down the hill, put your left hand
on the steering wheel at the 12 o’clock position.
This way, you will be able to tell if your wheels are
straight and maneuver as you back down. It is best
that you back down the hill with your wheels straight
rather than in the left or right direction. Turning the
wheel too far to the left or right will increase the
possibility of a rollover.
4-24

There are also some things you must not do if you stall,
or are about to stall, when going up a hill:
Never attempt to prevent a stall by shifting into
NEUTRAL (N) to rev-up the engine and regain
forward momentum. This will not work. Your vehicle
will roll backwards very quickly and you could go
out of control.
Instead, apply the regular brake to stop the
vehicle. Then apply the parking brake. Shift to
REVERSE (R), release the parking brake,
and slowly back straight down.
Never attempt to turn around if you are about to
stall when going up a hill. If the hill is steep
enough to stall your vehicle, it is steep enough to
cause you to roll over if you turn around. If you
cannot make it up the hill, you must back straight
down the hill.
If, after stalling, you try to back down the hill and decide
you just cannot do it, set the parking brake. If you
have an automatic transmission, shift to PARK (P).
Turn off the engine. Leave the vehicle and go get
some help. Exit on the uphill side and stay clear of
the path the vehicle would take if it rolled downhill.
Do not shift the transfer case to NEUTRAL when you
leave the vehicle. Leave it in some gear.
{CAUTION:
Shifting the transfer case to NEUTRAL
can cause your vehicle to roll even if the
transmission is in PARK (P), or, if you have a
manual transmission, even if you are in gear.
This is because the NEUTRAL position on the
transfer case overrides the transmission. 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),
or, put the manual transmission in FIRST (1).
But do not shift the transfer case to
NEUTRAL. Leave the transfer case in the
Four-Wheel High, Four-Wheel-High Lock,
or Four-Wheel-Low Lock position.
4-25

Driving Downhill
When off-roading takes you downhill, you will want to
consider a number of things:
How steep is the downhill? Will I be able to maintain
vehicle control?
What is the surface like? Smooth? Rough?
Slippery? Hard-packed dirt? Gravel?
Are there hidden surface obstacles? Ruts? Logs?
Boulders?
What is at the bottom of the hill? Is there a hidden
creek bank or even a river bottom with large rocks?If you decide you can go down a hill safely, then try to
keep your vehicle headed straight down, and use a
low gear. This way, engine drag can help your brakes
and they will not have to do all the work. Descend
slowly, keeping your vehicle under control at all times.
{CAUTION:
Heavy braking when going down a hill can
cause your brakes to overheat and fade.
This could cause loss of control and a serious
accident. Apply the brakes lightly when
descending a hill and use a low gear to
keep vehicle speed under control.
4-26

There some things not to do when driving down a hill.
These are important because, if you ignore them,
you could lose control and have a serious accident:
When driving downhill, avoid turns that take
you across the incline of the hill. A hill that is not
too steep to drive down may be too steep to
drive across. You could roll over if you do not
drive straight down.
Never go downhill with the transmission in
NEUTRAL (N). This is called “free-wheeling.”
Your brakes will have to do all the work and
could overheat and fade.
Your vehicle is much more likely to stall when going
uphill. But if it happens when going downhill:
1. Stop your vehicle by applying the regular brakes.
Apply the parking brake.
2. If you have an automatic transmission, shift to
PARK (P). While still braking, restart the engine.
3. Shift back to a low gear, release the parking brake,
and drive straight down.
4. If the engine will not start, get out and get help.
Driving Across an Incline
Sooner or later, an off-road trail will probably go
across the incline of a hill. If this happens, you have
to decide whether to try to drive across the incline.
Here are some things to consider:
{CAUTION:
Driving across an incline that is too steep will
make your vehicle roll over. You could be
seriously injured or killed. If you have any
doubt about the steepness of the incline, do
not drive across it. Find another route instead.
A hill that can be driven straight up or down may
be too steep to drive across. When you go straight
up or down a hill, the length of the wheel base — the
distance from the front wheels to the rear
wheels — reduces the likelihood the vehicle will
tumble end over end. But when you drive across an
incline, the much more narrow track width — the
distance between the left and right wheels — may
not prevent the vehicle from tilting and rolling over.
Also, driving across an incline puts more weight on
the downhill wheels. This could cause a downhill
slide or a rollover.
4-27

If the water is not too deep, drive slowly through it.
At faster speeds, water splashes on your ignition system
and your vehicle can stall. Stalling can also occur if
you get your tailpipe under water. And, as long as
your tailpipe is under water, you will never be able
to start your engine. When you go through water,
remember that when your brakes get wet, it may
take you longer to stop.
SeeDriving in Rain and on Wet Roads on page 4-33for
more information on driving through water.
After Off-Road Driving
Remove any brush or debris that has collected on
the underbody, chassis, or under the hood. These
accumulations can be a re hazard.
After operation in mud or sand, have the brake linings
cleaned and checked. These substances can cause
glazing and uneven braking. Check the engine and
oil coolers and underbody skid shields for mud
accumulation. Thoroughly and carefully clean these
devices to allow proper cooling. Check the bodystructure, steering, suspension, underbody shields,
wheels, tires, and exhaust system for damage. Also,
check the fuel lines and cooling system for any leakage.
Your vehicle will require more frequent service due
to off-road use. See the Maintenance Schedule
for additional information.
Assist Steps
If your vehicle has removable side steps, remove the
steps prior to off-roading to give your vehicle more ground
clearance and to prevent damage to the vehicle from the
side steps dragging and/or catching on obstacles.
Notice:Do not drive off-road with the side steps
attached to your vehicle. You can damage the
side steps and/or your vehicle’s frame if they get
caught or drag against an obstacle. This damage
would not be covered by your vehicle’s warranty.
Always remove the side steps prior to any off-road
driving.
4-31