transmission GMC SIERRA 2007 Service Manual

Q:Suppose, after stalling, I try to back down
the hill and decide I just cannot do it. What
should I do?
A:Set the parking brake, put the transmission in
PARK (P) and 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). 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). But do not shift
the transfer case to NEUTRAL. Leave the
transfer case in the Two-Wheel High,
Four-Wheel High or Four-Wheel Low
position.
400

Q:Are there some things I should not do
when driving down a hill?
A:Yes! 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.”
The brakes will have to do all the work
and could overheat and fade.
Q:Am I likely to stall when going downhill?
A:It is much more likely to happen going
uphill. But if it happens going downhill, here is
what to do.
1. Stop your vehicle by applying the regular
brakes. Apply the parking brake.
2. Shift to PARK (P) and, 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.
402

Hill and Mountain Roads
Driving on steep hills or mountains is different
from driving in at or rolling terrain.If you drive regularly in steep country, or if you are
planning to visit there, here are some tips that
can make your trips safer and more enjoyable. See
Off-Road Driving on page 390for information
about driving off-road.
Keep your vehicle in good shape. Check all
uid levels and also the brakes, tires,
cooling system, and transmission. These parts
can work hard on mountain roads.
{CAUTION:
If you do not shift down, the brakes 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. Shift down to let the engine assist
the brakes on a steep downhill slope.
416

{CAUTION:
Coasting downhill in NEUTRAL (N) or with
the ignition off is dangerous. The brakes
will have to do all the work of slowing
down. 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 your vehicle in gear
when you go downhill.
Know how to go down hills. The most important
thing to know is this: let your engine do some of
the slowing down. Shift to a lower gear when
you go down a steep or long hill.
Know how to go uphill. You may want to shift
down to a lower gear. The lower gears help
cool your engine and transmission, and you can
climb the hill better.
Stay in your own lane when driving on two-lane
roads in hills or mountains. Do not swing wide
or cut across the center of the road. Drive at
speeds that let you stay in your own lane.
As you go over the top of a hill, be alert. There
could be something in your lane, like a stalled
car or an accident.
You may see highway signs on mountains that
warn of special problems. Examples are long
grades, passing or no-passing zones, a falling
rocks area, or winding roads. Be alert to these
and take appropriate action.
417

You will need a well-charged battery to restart the
vehicle, and possibly for signaling later on with
your headlamps. Let the heater run for a while.
Then, shut the engine off and close the window
almost all the way to preserve the heat. Start
the engine again and repeat this only when you
feel really uncomfortable from the cold. But do it as
little as possible. Preserve the fuel as long as
you can. To help keep warm, you can get out of
the vehicle and do some fairly vigorous exercises
every half hour or so until help comes.
If Your Vehicle is Stuck in Sand,
Mud, Ice, or Snow
In order to free your vehicle when it is stuck, you
need to spin the wheels, but you do not want
to spin the wheels too fast. The method known as
rocking can help you get out when you are
stuck, but you must use caution.
{CAUTION:
If you let your vehicle’s tires spin at high
speed, they can explode, and you or
others could be injured. And, the
transmission or other parts of the vehicle
can overheat. That could cause an engine
compartment re or other damage. When
you are stuck, spin the wheels as little as
possible. Do not spin the wheels above
35 mph (55 km/h) as shown on the
speedometer.
422

Notice:Spinning the wheels can destroy parts
of your vehicle as well as the tires. If you
spin the wheels too fast while shifting
the transmission back and forth, you can
destroy the transmission.
For information about using tire chains on your
vehicle, seeTire Chains on page 574.
Rocking Your Vehicle to Get It Out
First, turn the steering wheel left and right.
That will clear the area around the front wheels. If
you have a four-wheel-drive vehicle, shift into
Four-Wheel High. If your vehicle has StabiliTrak
®,
you should turn the system off. SeeStabiliTrak®
System on page 381. Then shift back and
forth between REVERSE (R) and a forward gear,
spinning the wheels as little as possible.Release the accelerator pedal while you shift, and
press lightly on the accelerator pedal when the
transmission is in gear. By slowly spinning
the wheels in the forward and reverse directions,
you will cause a rocking motion that may free
your vehicle. If that does not get your vehicle out
after a few tries, it may need to be towed out.
Or, you can use the recovery hooks if your vehicle
has them. If your vehicle does need to be towed
out, seeTowing Your Vehicle on page 439.
423

Here are some important things to consider before
you do recreational vehicle towing:
What’s the towing capacity of the towing
vehicle? Be sure you read the tow vehicle
manufacturer’s recommendations.
How far will you tow? Some vehicles have
restrictions on how far and how long they
can tow.
Do you have the proper towing equipment?
See your dealer or trailering professional
for additional advice and equipment
recommendations.
Is your vehicle ready to be towed? Just as
you would prepare your vehicle for a long
trip, you’ll want to make sure your vehicle is
prepared to be towed. SeeBefore Leaving on
a Long Trip on page 414.
Dinghy Towing
Two-Wheel-Drive Vehicles
Notice:If you tow your vehicle with all
four wheels on the ground, the drivetrain
components could be damaged. The repairs
would not be covered by your warranty. Do not
tow your vehicle with all four wheels on the
ground.
Two-wheel-drive vehicles should not be towed
with all four wheels on the ground.
Two-wheel-drive transmissions have no provisions
for internal lubrication while being towed.
440

Four-Wheel-Drive Vehicles
Use the following procedure to tow your vehicle:
1. Shift the transmission to PARK (P).
2. Turn the engine off, but leave the ignition on.
3. Firmly set the parking brake.
4. Securely attach the vehicle being towed to the
tow vehicle.
{CAUTION:
Shifting a four-wheel-drive vehicle’s
transfer case into NEUTRAL can cause
your vehicle to roll even if the
transmission is in PARK (P). You or
others could be injured. Make sure the
parking brake is rmly set before you shift
the transfer case to NEUTRAL.
5. Shift the transfer case to NEUTRAL. See
Four-Wheel Drive on page 147for the
proper procedure to select the neutral position
for your vehicle.
6. Release the parking brake only after the
vehicle being towed is rmly attached to
the towing vehicle.
7. Turn the ignition off and leave the steering
column unlocked.
441

Dolly Towing
Front Towing (Front Wheels Off the
Ground)
Two-Wheel-Drive Vehicles
Notice:If you tow a two-wheel-drive vehicle
with the rear wheels on the ground, the
transmission could be damaged. The repairs
would not be covered by your warranty. Never
tow your vehicle with the rear wheels on the
ground.
Two-wheel-drive vehicles should not be towed
with the rear wheels on the ground.
Two-wheel-drive transmissions have no provisions
for internal lubrication while being towed.
To dolly tow a two-wheel-drive vehicle, you must
tow the vehicle with the rear wheels on the
dolly. See “Rear Towing (Rear Wheels Off the
Ground)” later in this section for more information.
Four-Wheel-Drive Vehicles
Use the following procedure to tow your vehicle:
1. Drive the vehicle up onto the tow dolly.
2. Shift the transmission to PARK (P).
3. Turn the engine off, but leave the ignition on.
4. Firmly set the parking brake.
5. Securely attach the vehicle being towed to the
tow dolly.
442

{CAUTION:
Shifting a four-wheel-drive vehicle’s
transfer case into NEUTRAL can cause
your vehicle to roll even if the
transmission is in PARK (P). You or
others could be injured. Make sure the
parking brake is rmly set before you shift
the transfer case to NEUTRAL.
6. Shift the transfer case to NEUTRAL. See
Four-Wheel Drive on page 147for the
proper procedure to select the neutral position
for your vehicle.
7. Release the parking brake only after the
vehicle being towed is rmly attached to
the towing vehicle.
8. Turn the ignition off and lock the steering
column.
Rear Towing (Rear Wheels Off the
Ground)
Two-Wheel-Drive Vehicles
Use the following procedure to tow your vehicle
from the rear:
1. Drive the vehicle onto the dolly.
2. Firmly set the parking brake. SeeParking
Brake on page 162.
3. Put the transmission in PARK (P).
4. Follow the dolly manufacturer’s instructions to
attach and secure the vehicle being towed to
the dolly and then the loaded dolly to the
tow vehicle. Make sure the wheels are straight
before towing.
Use an adequate clamping device to ensure
that the front wheels are locked into the
straight position.
5. Release the parking brake only after the
vehicle being towed is rmly attached to
the tow vehicle.
6. Turn the ignition to LOCK.
443