wheel HUMMER H3 2009 Service Manual

Scanning the Terrain
Off-road driving can take you over
many different kinds of terrain.
Be familiar with the terrain and its
many different features.
Surface Conditions:Off-roading
surfaces can be hard-packed
dirt, gravel, rocks, grass, sand,
mud, snow, or ice. Each of these
surfaces affects the vehicle’s
steering, acceleration, and braking
in different ways. Depending on
the surface, slipping, sliding, wheel
spinning, delayed acceleration,
poor traction, and longer braking
distances can occur.
Surface Obstacles:Unseen or
hidden obstacles can be hazardous.
A rock, log, hole, rut, or bump
can startle you if you are not
prepared for them. Often these
obstacles are hidden by grass,
bushes, snow, or even the rise and
fall of the terrain itself.Some things to consider:Is the path ahead clear?
Will the surface texture change
abruptly up ahead?
Does the travel take you uphill or
downhill?
Will you have to stop suddenly or
change direction quickly?
When driving over obstacles or
rough terrain, keep a rm grip on the
steering wheel. Ruts, troughs, or
other surface features can jerk the
wheel out of your hands.
When driving over bumps, rocks, or
other obstacles, the wheels can
leave the ground. If this happens,
even with one or two wheels,
you cannot control the vehicle as
well or at all.
Because you will be on an unpaved
surface, it is especially important
to avoid sudden acceleration,
sudden turns, or sudden braking.Off-roading requires a different
kind of alertness from driving on
paved roads and highways. There
are no road signs, posted speed
limits, or signal lights. Use
good judgment about what is safe
and what is not.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° minimum
approach (A), 75° maximum
approach angle (B).
Driving Your Vehicle 4-19

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.
Roll The 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, the
vehicle will cross logs up to
10 inches (25.4 cm) in diameter.
Approach the log at approximately a
15° angle (A) with the transmission
in 1 (First) and the transfer case
in Four-Wheel-Low Lock and “walk”
the vehicle over, one tire at a
time. It may be necessary to
modulate the brake pedal and
accelerator to avoid spin-out. Ease
the vehicle down from the log
with the brake.Driving on Hills
Off-road driving often takes you up,
down, or across a hill. Driving
safely on hills requires good
judgment and an understanding of
what the vehicle can and cannot do.
There are some hills that simply
cannot be driven, no matter how well
built the vehicle.
{CAUTION
Many hills are simply too steep for
any vehicle. If you drive up them,
you will stall. If you drive down
them, you cannot control your
speed. If you drive across them,
you will roll over. You could be
seriously injured or killed. If you
have any doubt about the
steepness, do not drive the hill.
4-20 Driving Your Vehicle

Approaching a Hill
When you approach a hill, decide
if it is too steep to climb, descend, or
cross. Steepness can be hard to
judge. On a very small hill, for
example, there may be a smooth,
constant incline with only a
small change in elevation where
you can easily see all the way to the
top. On a large hill, the incline
may get steeper as you near the
top, but you might not see this
because the crest of the hill
is hidden by bushes, grass, or
shrubs.
Consider this as you approach
a hill:
Is there a constant incline, or
does the hill get sharply
steeper in places?
Is there good traction on the
hillside, or will the surface
cause tire slipping?
Is there a straight path up or
down the hill so you will not have
to make turning maneuvers?
Are there obstructions on the hill
that can block your path, such
as boulders, trees, logs, or ruts?
What is beyond the hill? Is there
a cliff, an embankment, a
drop-off, a fence? Get out and
walk the hill if you do not know. It
is the smart way to nd out.
Is the hill simply too rough?
Steep hills often have ruts,
gullies, troughs, and exposed
rocks because they are
more susceptible to the effects
of erosion.
See “Hill Start Assist” underBraking
on page 4-3for information on
vehicles stopped on a grade.
Driving Uphill
Once you decide it is safe to drive
up the hill:
Use transmission and transfer
case low gear and get a rm
grip on the steering wheel.
Get a smooth start up the hill
and try to maintain speed.
Not using more power than
needed can avoid spinning the
wheels or sliding.
Let the traction system work to
control any wheel slippage.
The traction control system
allows for moderate wheel spin
with some capability to dig in and
power up the hill.
Driving Your Vehicle 4-21

While backing down the hill, put
your left hand on the steering
wheel at the 12 o’clock position
so you can tell if the wheels
are straight and can maneuver
as you back down. It is best
to back down the hill with
the 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.
Things not to do if the vehicle stalls,
or is about to stall, when going
up a hill:
Never attempt to prevent a stall
by shifting into N (Neutral) to
rev-up the engine and regain
forward momentum. This will
not work. The vehicle can
roll backward very quickly and
could go out of control.
Never try to turn around if about
to stall when going up a hill. If
the hill is steep enough to
stall the vehicle, it is steep
enough to cause it to roll over. If
you cannot make it up the hill,
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 the vehicle has an automatic
transmission, shift to P (Park). 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
P (Park). 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 P (Park). But do not shift the
transfer case to Neutral.
Driving Your Vehicle 4-23

Driving Downhill
When off-roading takes you
downhill, consider:
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, try to keep the vehicle
headed straight down. Use a low
gear so engine drag can help
the brakes so they do not have to
do all the work. Descend slowly,
keeping the 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.
Things not to do when driving down
a hill:
When driving downhill, avoid
turns that take you across
the incline of the hill. A hill that
is not too steep to drive down
might be too steep to drive
across. The vehicle could
roll over.
Never go downhill with the
transmission in N (Neutral), called
free-wheeling. The brakes will
have to do all the work and could
overheat and fade.Vehicles are much more likely to
stall when going uphill, but if it
happens when going downhill:
1. Stop the vehicle by applying the
regular brakes and apply the
parking brake.
2. With an automatic transmission,
shift to P (Park). 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.
4-24 Driving Your Vehicle

Driving Across an Incline
An off-road trail will probably go
across the incline of a hill. To decide
whether to try to drive across the
incline, consider the following:
{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 might be
too steep to drive across. When
going straight up or down a
hill, the length of the wheel
base — the distance from
the front wheels to the rear
wheels —reduces the likelihoodthe vehicle will tumble end over
end. But when driving across
an incline, the narrower
track width — the distance
between the left and right
wheels — might not prevent the
vehicle from tilting and rolling
over. Driving across an incline
puts more weight on the downhill
wheels which could cause a
downhill slide or a rollover.
Surface conditions can be a
problem. Loose gravel, muddy
spots, or even wet grass can
cause the tires to slip sideways,
downhill. If the vehicle slips
sideways, it can hit something
that will trip it — a rock, a rut,
etc. — and roll over.
Hidden obstacles can make the
steepness of the incline even
worse. If you drive across a rock
with the uphill wheels, or if the
downhill wheels drop into a rut or
depression, the vehicle can tilt
even more.
For these reasons, carefully
consider whether to try to drive
across an incline. Just because the
trail goes across the incline does
not mean you have to drive it.
The last vehicle to try it might have
rolled over.
If you feel the vehicle starting to
slide sideways, turn downhill. This
should help straighten out the
vehicle and prevent the side
slipping. The best way to prevent
this is to “walk the course” rst,
so you know what the surface is like
before driving it.
Driving Your Vehicle 4-25

Stalling on an Incline
{CAUTION
Getting out on the downhill (low)
side of a vehicle stopped across
an incline is dangerous. If the
vehicle rolls over, you could be
crushed or killed. Always get out
on the uphill (high) side of the
vehicle and stay well clear of the
rollover path.
If the vehicle stalls when crossing
an incline, be sure you, and
any passengers, get out on the
uphill side, even if the door there is
harder to open. If you get out on
the downhill side and the vehicle
starts to roll over, you will be right in
its path.
If you have to walk down the slope,
stay out of the path the vehicle
will take if it does roll over.
Driving in Mud, Sand, Snow,
or Ice
When you drive in mud, snow, or
sand, the wheels do not get good
traction. Acceleration is not as quick,
turning is more difficult, and braking
distances are longer.
It is best to use a low gear when in
mud — the deeper the mud, the
lower the gear. In really deep mud,
keep the vehicle moving so it
does not get stuck.
When driving on sand, wheel
traction changes. On loosely packed
sand, such as on beaches or
sand dunes, the tires will tend to
sink into the sand. This affects
steering, accelerating, and braking.
Drive at a reduced speed and
avoid sharp turns or abrupt
maneuvers.Hard packed snow and ice offer the
worst tire traction. On these surfaces,
it is very easy to lose control. On wet
ice, for example, the traction is so
poor that you will have difficulty
accelerating. And, if the vehicle does
get moving, poor steering and
difficult braking can cause it to slide
out of control.
{CAUTION
Driving on frozen lakes, ponds, or
rivers can be dangerous.
Underwater springs, currents
under the ice, or sudden thaws
can weaken the ice. Your vehicle
could fall through the ice and you
and your passengers could
drown. Drive your vehicle on safe
surfaces only.
4-26 Driving Your Vehicle

Driving in Water
{CAUTION
Driving through rushing water can
be dangerous. Deep water can
sweep your vehicle downstream
and you and your passengers
could drown. If it is only shallow
water, it can still wash away the
ground from under your tires, and
you could lose traction and roll
the vehicle over. Do not drive
through rushing water.
Heavy rain can mean ash ooding,
and ood waters demand extreme
caution.Find out how deep the water is
before driving through it. Do not
try it if it is deep enough to cover
the wheel hubs, axles, or exhaust
pipe — you probably will not get
through. Deep water can damage the
axle and other vehicle parts. The
vehicle is capable of depths up to
20 inches (50 cm). Know how to
judge whether the water is deeper
than this before proceeding into it.
If the water is not too deep, drive
slowly through it. At faster speeds,
water splashes on the ignition
system and the vehicle can stall.
Stalling can also occur if you get the
tailpipe under water. If the tailpipe
is under water, you will never
be able to start the engine. When
going through water, remember that
when the brakes get wet, it might
take longer to stop. SeeDriving
in Rain and on Wet Roads on
page 4-29.
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
for mud accumulation. Thoroughly
and carefully clean these devices to
allow proper cooling. Check the
body structure, steering, suspension,
wheels, tires, and exhaust system
for damage and check the fuel lines
and cooling system for any
leakage.
The vehicle requires more frequent
service due to off-road use.
Refer to the Maintenance Schedule
for additional information.
Driving Your Vehicle 4-27

{CAUTION
Coasting downhill in N (Neutral)
or with the ignition off is
dangerous. The brakes will have
to do all the work of slowing down
and they could get so hot that
they would not work well. You
would then have poor braking or
even none going down a hill. You
could crash. Always have the
engine running and the vehicle in
gear when going downhill.
Stay in your own lane. Do not
swing wide or cut across the
center of the road. Drive at
speeds that let you stay in your
own lane.
Top of hills: Be alert — something
could be in your lane (stalled car,
accident).
Pay attention to special road
signs (falling rocks area, winding
roads, long grades, passing or
no-passing zones) and take
appropriate action.
SeeOff-Road Driving on page 4-13
for information about driving
off-road.
Winter Driving
Driving on Snow or Ice
Drive carefully when there is snow
or ice between the tires and the
road, creating less traction or grip.
Wet ice can occur at about 32°F
(0°C) when freezing rain begins to
fall, resulting in even less traction.
Avoid driving on wet ice or in
freezing rain until roads can be
treated with salt or sand.
Drive with caution, whatever the
condition. Accelerate gently
so traction is not lost. Accelerating
too quickly causes the wheelsto spin and makes the surface
under the tires slick, so there is even
less traction.
Try not to break the fragile traction. If
you accelerate too fast, the drive
wheels will spin and polish the
surface under the tires even more.
TheTraction Control System (TCS)
on page 4-7improves the ability
to accelerate on slippery roads, but
slow down and adjust your driving
to the road conditions. When driving
through deep snow, turn off the
traction control system to help
maintain vehicle motion at lower
speeds.
TheAntilock Brake System (ABS)
on page 4-5improves vehicle
stability during hard stops on a
slippery roads, but apply the brakes
sooner than when on dry pavement.
Driving Your Vehicle 4-31

Run the engine for short periods
only as needed to keep warm,
but be careful.
To save fuel, run the engine for
only short periods as needed to
warm the vehicle and then shut the
engine off and close the window
most of the way to save heat.
Repeat this until help arrives
but only when you feel really
uncomfortable from the cold. Moving
about to keep warm also helps.
If it takes some time for help to
arrive, now and then when you run
the engine, push the accelerator
pedal slightly so the engine
runs faster than the idle speed. This
keeps the battery charged to
restart the vehicle and to signal for
help with the headlamps. Do
this as little as possible to save fuel.If Your Vehicle is
Stuck in Sand, Mud,
Ice, or Snow
Slowly and cautiously spin the
wheels to free the vehicle when
stuck in sand, mud, ice, or snow.
SeeRocking Your Vehicle to Get It
Out on page 4-34.
If the vehicle has a traction system,
it can often help to free a stuck
vehicle. Refer to the vehicle’s
traction system in the Index. If stuck
too severely for the traction
system to free the vehicle, turn the
traction system off and use the
rocking method.
{CAUTION
If you let your vehicle’s tires spin
at high speed, they can explode,
and you or others could be
injured. The vehicle can overheat,
causing an engine compartment
re or other damage. Spin the
wheels as little as possible and
avoid going above 35 mph
(55 km/h) as shown on the
speedometer.
For information about using tire
chains on the vehicle, seeTire
Chains on page 5-65.
Driving Your Vehicle 4-33