1999 GMC C-SERIES Owners Manual

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6-51 When It's Time for New Tires
Replace your tires when the tread depth is down to
1/8 of an inch (3.2 mm) for the front tires, or 1/16 of
an inch (1.6 mm) for a rear tire. Also, you need a new
tire if:

You can see cord or fabric showing through the
tire's rubber.

The tread or sidewall is cracked, cut or snagged deep
enough to show cord or fabric.

The tire has a bump, bulge or split.

The tire has a puncture, cut or other damage that
can't be repaired well because of the size or location
of the damage.
CAUTION:
Mixing tires could cause you to lose control while
driving. If you mix tires of different types
-- like
radial and bias
-belted tires -- the vehicle may not
handle properly, and you could have a crash.
Be sure to use the same type of tires all around.
When you replace tires, make sure they are the same
size, load range, speed rating and construction type
(bias, bias
-belted or radial) as your original tires.
Wheel Alignment and Tire Balance
The wheels on your vehicle were aligned at the
factory to give you the longest tire life and best
overall performance.
Proper front wheel alignment must be maintained in
order to ensure efficient steering, good directional
stability, and prevent abnormal tire wear. If you notice
unusual tire wear or your vehicle is pulling one way or
the other, the alignment may need to be reset. If you
notice your vehicle vibrating when driving on a smooth
road, your wheels may need to be balanced.
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6-52 Tightening the Wheel Nuts
CAUTION:
Wheel nuts that are not tight can work loose. If
all the nuts on a wheel come off, the wheel can
come off the vehicle, causing a serious crash. All
wheel nuts must be properly tightened. Follow
the rules in this section to be sure they are.
This section lets you know how often to check the
tightness of the wheel nuts on your vehicle and how
tight they must be.
First, use these pictures to decide what kind of wheels
you have.
Hub-Piloted Type,
8
-HoleHub
-Piloted Type,
10
-Hole
Stud-Piloted Type, 10-Hole
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6-53
Then, follow the steps below for the wheels you have.
Cast
-Type Wheel
1. Put the tire and rim assembly on the axle hub.
2. Install the rim spacer at the rear.
3. Install the outer rear tire and rim assembly so that its
valve stem is exactly opposite the valve stem on the
inner tire and rim assembly.
4. Install the rim clamps and nuts. Position
them properly.
NOTICE:
If you tighten a nut when a rim clamp is not
positioned properly, it can damage the rim and
also cause the wheel to wobble in operation. Be
sure to position the rim clamps properly before
you go on to the next step.
5. Finger-tighten the nuts. Be sure that all of the wheel
clamps are seated all the way around the wheel.
6. Tighten all of the nuts using the following diagram.
Be sure to use the one that matches your wheels.
7. Now repeat Step 6, but this time tighten the nuts to
200 lb
-ft (271 N´m) of torque.
8. Turn the wheel and measure along the sidewall to see
how much wheel run
-out there is. There should be
no more than 1/8 inch (3 mm) on the front wheels
and 3/16 inch (5 mm) on the rear wheels. If there is
too much wheel run
-out, you can try loosening the
nuts on the side where there is the most run
-out and
tightening the opposite nuts. When you finally have
the tire running true, tighten all of the nuts to
200 lb
-ft (271 N´m).
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6-54
Stud-Piloted 10-Stud Wheel
The studs and nuts used on the right side of the vehicle
have right
-hand threads. Those used on the left side
have left
-hand threads. It is easy to tell by looking at the
nuts, because they are stamped R or L.
1. Put the tire and rim assembly on the axle hub.
2. Put on the wheel nuts. If you use oil or grease on the
wheel studs or nuts, the wheel nuts can't tighten
properly. This could let the wheel come off as you
are driving.
3. Finger
-tighten the nuts on the rear inner wheels and
the front wheels.
4. Tighten these nuts to 575 lb
-ft (780 N´m), unless
you have aluminum wheels and/or aluminum hubs.
If you have aluminum wheels and/or aluminum
hubs, tighten the nuts only to 475 lb
-ft (644 N´m).
Use the following diagram to do this.
Front or Inner Dual
WheelOuter Dual Wheel
5. Install the outer rear tire and rim assembly so that its
valve stem is exactly opposite the valve stem on the
inner tire and rim assembly.
6. Put on the wheel nuts.
7. Finger
-tighten the wheel nuts.
8. Tighten the nuts to the same torque numbers shown
in Step 4.
Whenever tightening both the inner and outer rear wheel
nuts, first loosen the outer wheel nuts. Then tighten the
inner nuts. Finally, tighten the outer nuts.
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6-55
CAUTION:
Never use oil or grease on studs or nuts. If you
do, the nuts might come loose. Your wheel could
fall off, causing a serious accident.
Hub-Piloted Wheels, 8-Hole or 10-Hole
The studs and nuts used with these wheels have
right
-hand threads.
1. With intermittent pilot pads, position a pad at
12 o'clock to center the wheel and reduce run
-out.
2. Put the tire and rim assembly on the axle hub. Install
the outer rear tire and rim assembly so that its valve
stem is exactly opposite the valve stem on the inner
tire and rim assembly.
3. Put on the wheel nuts.
4. Finger
-tighten the nuts.
5. Oil the surfaces between
the nuts and washers as
shown. Do not oil the
studs or the threads of
the nut.
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6-56
6. Tighten the nuts to
400 lb
-ft (542 N´m)
if an eight
-hole stud or
480 lb
-ft (650 N´m)
if a 10
-hole stud, use
the following diagrams.
8
-Hole
10-Hole
(Front or Inner Dual
Wheel)10-Hole
(Outer Dual Wheel)
CAUTION:
If wheel studs are damaged, they can break. If all
the studs on a wheel broke, the wheel could come
off and cause a serious crash. If any stud is
damaged because of a loose
-running wheel, it
could be that all of the studs are damaged. To be
sure, replace all studs on the wheel. If the stud
holes in a wheel have become larger, the wheel
could collapse in operation. Replace any wheel if
its stud holes have become larger or distorted in
any way. Inspect hubs and hub piloted wheels for
damage. Because of loose running wheels,
piloting pad damage may occur and require
replacement of the entire hub, for proper
centering of the wheels.
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6-57
CAUTION:
Rust or dirt on a wheel, or on the parts to which
it is fastened, can make the wheel nuts become
loose after a time. The wheel could come off and
cause an accident. When you change a wheel,
remove any rust or dirt from the places where the
wheel attaches to the vehicle. In an emergency,
you can use a cloth or paper towel to do this; but
be sure to use a scraper or wire brush later, if you
need to, to get all the rust or dirt off.
How Often to Check
Wheel tightness is so important you should have a
technician check nut tightness on all wheels with a
torque wrench every 1,000 miles (1 600 km).
When your vehicle is new or when a wheel or fastener is
new you should have a technician tighten the wheel
stud and rim clamp nuts, with a torque wrench, at
100, 500 and 1,000 miles (160, 800 and 1 600 km).
The reason for this is that the clamping system has to
seat before the fasteners will stay tightened.
Wheel Replacement
Replace any wheel that is bent, cracked or badly rusted.
If wheel nuts keep coming loose, replace the wheel.
If the wheel leaks air, replace it.
Your dealer will know the kind of wheel you need.
CAUTION:
A leaking wheel could fail without warning. A
wheel designed for tubeless tires could be leaking
because it is damaged. Don't use an inner tube or
some other thing to try to stop the leaking. Get a
new wheel of the proper type.
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6-58
CAUTION:
Without the correct wheel, you may not be able
to stop properly, and you could have other
problems like a tire air
-out. You could have a
collision. If you don't go to your dealer to get a
new wheel, be sure you get the correct one. Each
new wheel should match the original wheel in
load
-carrying capacity, inflation pressure
capacity, diameter, width, offset and mounting
configuration.
Using wheels and tires with higher load-carrying limits
than the original wheels and tires doesn't change the
GAWR or the GVWR of your vehicle.
NOTICE:
The wrong wheel can cause trouble in bearing
life, brake cooling, speedometer/odometer
calibration, headlamp aim, bumper height,
vehicle ground clearance, stopping distance and
tire clearance to the body and chassis. You could
also have other problems like a tire air
-out.
Used Replacement Wheels
CAUTION:
Putting a used wheel on your vehicle is
dangerous. You can't know how it's been used or
how many miles it's been driven. It could fail
suddenly and cause an accident. If you have to
replace a wheel, use a new GM original
equipment wheel.
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