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Air Brake Systems
If your vehicle has air brakes, it is important to get rid of
moisture in your system. Moisture will damage your
system if it is not removed daily.
There are two ways to do this. One is automatic through
the air brake vehicle’s air dryer with intregal automatic
moisture ejector that purges air from the system through
a self-contained reservoir. The other way to drain
moisture from the air brake system is to manually
activate drain valves at each reservoir. Drain the air
reservoirs occasionally to be sure the air dryer is
working properly.
Drain the air brakes at full system pressure. To be sure
you are at full pressure, check your air pressure
gage. It should read at least 100 psi (692 kPa).
Air Dryer
If your vehicle has air brakes, it will have an air dryer.
This collects and removes dirt, moisture, or other foreign
matter from the air prior to entering the brake system.
The dryer also acts as a moisture ejector. It
automatically ejects the moisture when the compressor
cycles. The purge tank has a manual drain valve
that must be drained every day. See “Air Brake
Systems” for the manual drain procedure. The air dryer
is mounted on the passenger side frame rail.
The dryer has a filter that you need to change at
intervals. SeeScheduled Maintenance on page 6-5for
more about servicing this filter.
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Electric Air Compressor
Your vehicle may have an electric air compressor. This
compressor is used to run options that require
pressurized air, such as air horn, air seat, 7.8L engine
exhaust restrictor, or 7.8L engine exhaust brake.
The air compressor is used when vehicles are not
equipped with an air brake system.
The air supply for this
system must be
maintained by releasing
the drain valve to eject any
moisture that may have
built up in the system.
It is recommended that this system be drained on a
weekly basis.
Clutch Pedal Free Travel
If you have a V8 engine and a manual transmission,
your clutch will need adjustment when pedal free travel
gets down to about 1/4 inch (32 mm), as measured
at the clutch pedal pad. You should have 1 1/2 to
2 inches (38 to 51 mm) of clutch pedal free travel.
If your clutch ever needs service, be sure to use only
GM clutch replacement parts.
Chassis Lubrication
Your Maintenance Schedule provides all of the required
chassis lubrication intervals and identifies proper
lubricants to use. Be sure to see your Maintenance
Schedule before performing any chassis lubrication
service. To determine location of chassis lubrication
items, use the following charts.
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Rear Axle
When to Check and Change Lubricant
Refer to the Maintenance Schedule to determine
how often to check the lubricant and when to change it.
SeeScheduled Maintenance on page 6-5.
Notice:If you drive your vehicle through deep
water that is higher than the front or rear axle, water
may enter the axle housing and cause the axle
lubricant to break down. This could damage
the gears inside. Avoid driving your vehicle through
deep water.
You should avoid driving your vehicle through deep
puddles or standing water. If you must drive through
water that is higher than the front or rear axle, see your
dealer immediately afterward to have the condition of
the axle lubricant checked.
How to Check Lubricant
To get an accurate reading, the vehicle should be on a
level surface.
If the level is below the bottom of the filler plug hole,
located on the rear axle, you’ll need to add some
lubricant. Add enough lubricant to raise the level to the
bottom of the filler plug hole.
What to Use
Refer to the Maintenance Schedule to determine what
kind of lubricant to use. SeePart C: Recommended
Fluids and Lubricants on page 6-33.
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Rear Axle Shift Motor
When to Check and Change Fluid
If you have an optional air-shift two-speed, controlled
traction, or locking differential type rear axle, a good time
to check the fluid level in the axle shift motor is when
the rear axle lubricant is checked. Use refrigerant
oil (shift motor only).
How to Check Fluid
Remove the plug on the front plate of the axle shift
motor, add enough fluid to raise the level to the bottom
of the filler plug hole, then replace the plug.
What to Use
Refer to your Maintenance Schedule to determine what
kind of lubricant to use. SeePart C: Recommended
Fluids and Lubricants on page 6-33.
Four-Wheel Drive
Transfer Case
When to Check Lubricant
It is not necessary to regularly check transfer case fluid
unless you suspect there is a leak or you hear an
unusual noise. A fluid loss could indicate a problem.
Have it inspected and repaired.
How to Check Lubricant
A. Fill Plug
B. Drain Plug
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To get an accurate reading, the vehicle should be on a
level surface.
If the level is below the bottom of the fill plug hole,
located on the transfer case, you’ll need to add some
lubricant. Add enough lubricant to raise the level to
the bottom of the fill plug hole. Use care not to
overtighten the plug.
When to Change Lubricant
Refer to the Maintenance Schedule to determine how
often to change the lubricant. SeeScheduled
Maintenance on page 6-5.
What to Use
Refer to the Maintenance Schedule to determine what
kind of lubricant to use. SeePart C: Recommended
Fluids and Lubricants on page 6-33.
Front Axle
When to Check Lubricant
It is not necessary to regularly check front axle fluid
unless you suspect there is a leak or you hear an
unusual noise. A fluid loss could indicate a problem.
Have it inspected and repaired.
Notice:If you drive your vehicle through deep
water that is higher than the front or rear axle, water
may enter the axle housing and cause the axle
lubricant to break down. This could damage
the gears inside. Avoid driving your vehicle through
deep water.
You should avoid driving your vehicle through deep
puddles or standing water. If you must drive through
water that is higher than the front or rear axle, see your
dealer immediately afterward to have the condition of
the axle lubricant checked.
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How to Check Lubricant
To get an accurate reading, the vehicle should be on a
level surface.
If the level is below the bottom of the filler plug hole,
you may need to add some lubricant.
Add enough lubricant to raise the level to the bottom of
the filler plug hole.
What to Use
To determine what kind of lubricant to use see
Part C: Recommended Fluids and Lubricants on
page 6-33.
Noise Control System
Tampering with Noise Control
System Prohibited
The following information relates to compliance with
federal noise emission standards for vehicles with
a Gross Vehicle Weight Rating (GVWR) of more than
10,000 lbs (4 536 kg). The Maintenance Schedule
provides information on maintaining the noise control
system to minimize degradation of the noise emission
control system during the life of your vehicle. The noise
control system warranty is given in your warranty
booklet.
These standards apply only to vehicles sold in the
United States.
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Other Service Items
Fuel Filter
Fuel Filter/Pressure Regulator
(Gasoline Engines)
The steel fuel filter/pressure regulator is located near
the engine compartment on the driver’s side frame rail.If your vehicle has a rear steel fuel tank, the fuel
filter/pressure regulator is located near the rear fuel
tank, on the driver’s side frame rail. SeeScheduled
Maintenance on page 6-5for recommended service
intervals.
If your vehicle is equipped with the optional Davco
spin-on type filter, it is located on the driver’s side
frame rail.
Fuel Filter (Diesel Engines)
If you have a diesel engine, your fuel filter is located in
the engine compartment on the driver’s side of the
vehicle, or along the driver’s side frame rail. See “Fuel
Filter Replacement” earlier in this section for further
information.
Also seeScheduled Maintenance on page 6-5for
recommended service intervals.
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Front Wheel Bearings with
Oil-Filled Hubs
Notice:If you drive your vehicle through deep
water that is higher than the front or rear axle, water
may enter the axle housing and cause the axle
lubricant to break down. This could damage
the gears inside. Avoid driving your vehicle through
deep water.
You should avoid driving your vehicle through deep
puddles or standing water. If you must drive through
water that is higher than the front or rear axle, see your
dealer immediately afterward to have the condition of
the axle lubricant checked.If your vehicle has oil-filled
hubs, occasionally check
to see if they have enough
oil. You can tell if there
is oil there by using
the circular gage on the
sight glass.
If there isn’t, clean the rubber fill plug in the center of
the glass, and then remove it. Be careful not to
allow any dirt or water to get into the oil. Add enough of
the recommended oil to bring it up to the level mark
that you’ll see on the glass.
Refer to your Maintenance Schedule for the proper oil
to use.
When you fill the hub, check the glass again after
driving a short distance. It takes a while for the oil to
flow through the system, and you may find that you have
to add a little more to fill it to the proper level. Be sure
not to overfill the hub.
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