Chevrolet Low Cab Forward Owner Manual (GMNA-Localizing-U.S.-
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Vehicle Care 277
Another characteristic of the HBB
system is that the brake pedal may
be depressed easily to the floor with
the vehicle at a stop. This is not a
sign of malfunction.
When the engine is running, the
system automatically charges the
accumulator whenever pressure has
been reduced after braking. Auto
charge may be activated without
braking, depending on temperature
changes in the accumulator. During
auto charge, a hissing and clicking
sound can be heard. This is not a
malfunction.
With the engine running, a booming
sound can be heard during hard
braking. This comes from the
brake-fluid pump. It is not a
malfunction.
Applying continuous hard braking
for a long time will lead to
considerable temperature rise in the
HBB pump. Such overworking of the
brakes is best avoided.Vacuum or hydraulic power
assisted brakes
If the engine stops, do not pump the
brakes. The system is designed to
stop the vehicle with reserve power
assist if the brake pedal is held
down. This reserve is greatly
reduced each time you apply and
release the brakes. If, when you
turn the steering wheel during
braking, the vehicle does not turn,
release some pressure from the
brake pedal.
In a Vehicle Equipped with a HBB,
Do Not Keep the Brake Pedal
Depressed for an Extended Period
Caution
Failure to follow the above
instruction will cause the oil inside
the HBB oil pump to get very hot.
This could damage the HBB tank
and deteriorate seals and also
could cause damage to the HBB
oil pump, HBB unit and/or HBB
hosing. Eventual leakage of HBB
(Continued)
Caution (Continued)
oil, sudden increase in brake
pedal resistance and fire could
unexpectedly result in an
accident.
Hydraulic Brake Booster (HBB)
Fluid (5500HD/5500XD Series)
The HBB system has been
designed to use ATF Dexron fluid is
used with this system, rubber
components may be damaged, oil
may leak and the system may
malfunction. It is important to
remember that the fluid used in the
hydro-booster is completely different
in characteristics from the brake
fluid used in the master and wheel
cylinders.
If hydro-booster fluid and brake fluid
from the master cylinder are
mistakenly mixed together and
used, rubber components will
deteriorate as a result of insufficient
lubrication. Any resultant oil leakage
or system malfunction can in turn
lead to dragging brakes or other
Chevrolet Low Cab Forward Owner Manual (GMNA-Localizing-U.S.-
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280 Vehicle Care
hose and pipe do not interfere with
any chassis part or wheel, and that
their joints are not leaking and are
free of any type of damage. Check
the right front brake hose and pipe
in the same way. The rear left and
right brake hoses and pipes should
also be checked in the same
manner.
Disc Brakes and Drum Brakes
If the brake pads and shoe linings
wear out beyond their usable limit,
not only will the brake performance
be impaired, but brake components
could also fail.
{Warning
Do not drive with brake pads and
shoe linings worn out beyond the
limit. Excessively worn brake
pads and shoe linings may cause
breakdown of brake components
and poor braking performance.
You and others could be seriously
injured.
Caution
The pad has an embedded wear
indicator. A squeaking noise from
the indicator means that the pad
is approaching the usable limit.
If the squeaking noise from the
indicator can be heard, contact
the nearest dealer for inspection
or replacement.
Brake Fluid
Checking the Brake Fluid
Level
Remove the inspection cover (1) on
the left- hand side of the instrument
panel by turning it with your fingers.
Check that the fluid level in the
reservoir is between the "MAX" and
"ADD" lines.
If the fluid surface cannot easily be
seen, rock the vehicle gently.
Adding Brake Fluid
If the level of brake fluid has
dropped below the "ADD" line,
remove the cap (2) and add fluid.
Take care to avoid filling beyond the
"MAX" line.
Tighten the cap securely after the
fluid has been added.
When adding brake fluid to the tank,
take care to prevent dirt and water
from entering it. Any dirt or water in
the system could cause the vehicle
to lose braking functions.
Inspect and change brake fluid
according to the Maintenance
Schedule.
Use the recommended brake fluid
when adding brake fluid.
Chevrolet Low Cab Forward Owner Manual (GMNA-Localizing-U.S.-
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318 Vehicle Care
Using worn-out tires is dangerous
because they might have an
increased chance of getting
punctured or bursting while driving.
Check all tires to see if tread wear
indicators appear on their treads
and also check their entire tread for
its depth with a depth gauge to
make sure that the grooves are
deeper than the specified depth.
A tire with tread wear indicators
appearing must be changed. Also,
check the tires for uneven or
otherwise abnormal wear.
{Warning
Tires with excessively shallow
tread grooves will increase the
chance of skidding and, when
driving at high speeds,
hydroplaning. You and others
could be seriously injured.
Hydroplaning occurs when a vehicle
is running at high speeds on a wet
road and a layer of water forms
between the road surface and tires
causing the tires to float on it.
Hydroplaning prevents the driver from steering correctly and from
slowing down the vehicle with the
brake pedal.
Use of Low Aspect Ratio Tires
1. Standard tire
2. Low aspect ratio tire
Low aspect ratio tires for truck
applications (aspect ratio at 70%)
have an air volume 20% to 30%
smaller than that of standard tires.
When air begins to leak, therefore,
low aspect ratio tires adversely
affect vehicle operation much faster
than standard tires. Check air
pressure of low aspect ratio tires
more often than standard tires using
a tire air pressure gauge.
Damaged Tires
{Warning
It is dangerous to mount the
wrong size tire on a wheel. If you
do so, the tire/wheel can explode
as air is being added. This
explosion may result in severe
personal injury or death. For the
3.0L diesel engine, to learn which
wheels and tires are correct, look
at the "VIN and Weight Rating
Plate" on the left side rear pillar
panel below the striker. For the
5.2L diesel engine, to learn which
wheels and tires are correct, look
at the "VIN, Weight Rating, and
Greenhouse Gas (GHG)
Emissions Plate" on the left side
rear pillar panel below the striker
(single cab) or on the left center
pillar panel beside the shoulder
seat belt anchor (crew cab).For
(Continued)
Chevrolet Low Cab Forward Owner Manual (GMNA-Localizing-U.S.-
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Vehicle Care 319
Warning (Continued)
gas engines, to learn which
wheels and tires are correct, look
at the "Vehicle Certification and
Greenhouse Gas (GHG)
Emissions Plate" on the left side
rear pillar panel below the striker
(single cab) or on the left center
pillar panel beside the shoulder
seat belt anchor (crew cab).
Wheel size is also stamped on
the side of each wheel.
To help avoid personal injury and
property damage if a wheel must
be changed, seek expert tire
services if you can. If you must
remove the wheel without any
such help, do the following:. If the tire looks as if it may
be underinflated, stand to
the side and check whether
the wheel assembly
appears normal by
comparing it to another
wheel assembly on the
vehicle.
(Continued)
Warning (Continued)
.Let the air out of the tire by
taking out the valve core.
If you have a way to put air
back in a tire, note that it is
good safety practice to let
the air out of both tires of a
dual assembly before taking
off the damaged tire and rim
assembly from the vehicle.
After letting out the air, take
off the tire and rim assembly
and install a spare tire and
rim assembly.
If your vehicle is equipped
with a differential lock
system or limited slip
differential (LSD), it might
start moving when the
engine power is transmitted
to the rear axle even when
one of the wheels on the
axle is raised clear of the
ground. Do not start the
engine with any rear wheel
in contact with the ground.
(Continued)
Warning (Continued)
If you are not fully
experienced on the
procedures to follow, and/or
are not equipped with the
proper tools and equipment,
again, do not attempt to
raise the vehicle, or remove
or install the tire and wheel
assembly—seek expert tire
services.
. Do not put air back in a tire
that has been run flat, or is
seriously low on air, without
first having the tire taken off
the wheel and the tire
checked for damage.
. Note that taking off and
mounting tires on wheels
requires proper tools, safety
equipment and special
training. A person can be
severely injured or killed
and damage can result from
using the wrong service
methods. Truck tires and
(Continued)
Chevrolet Low Cab Forward Owner Manual (GMNA-Localizing-U.S.-
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324 Vehicle Care
The difference in diameter of the
tires for a dual-tire wheel should be
within the limit specified in the table
below. If the limit is exceeded, the
tires wear more rapidly than they
should.
Steel Wheels
Aluminum/Steel Wheels
Vehicles with the aluminum wheel
option may have steel wheels on
the inner rear position. These
wheels must only be mounted on
the inner rear positions and should
only be rotated from side to side.
{Warning
If differently sized tires are used
between the front and rear axles,
do not exchange tires between
the front and rear axles;
otherwise, the tires get loaded
beyond their limits. This is highly (Continued)
Warning (Continued)
dangerous because the tires and
disc wheels could break down
under an excessive load. You and
others could be seriously injured.
Permissible diameter difference
Radial tire Within 8 mm (0.31 in)
The tightening torque of the wheel
nuts may decrease after a tire
change due to their initial
settlement. Upon driving 50 to
100 km (31 to 62 mi) after a tire
change, retighten the wheel nuts to
the specified torques according to
the instructions in "Retightening
Wheel Nuts" following.
See Maintenance Schedule 0345.
Retightening Wheel Nuts
Check the wheel nuts to make sure
they are tightened to the specific
torque by using a torque wrench.
Use the following methods to check
loose wheel nuts. The tightening
torque of the wheel nuts may
Chevrolet Low Cab Forward Owner Manual (GMNA-Localizing-U.S.-
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Vehicle Care 325
decrease after a tire change or
rotation due to their initial
settlement. After driving 50 to
100 km (31 to 62 mi), be sure to
retighten the wheel nuts to the
specified torque.
SeeMaintenance Schedule 0345.
Tightening torque
500 N·m (362 lb·ft)
Single Tire
1. Left side tire
2. Right side tire
Turn the wheel nuts in the tightening
direction to the specified torque. Retightening of nuts on left rear
dual-tire wheel
Dual Tire
Of the nuts on the wheel studs,
loosen the outer wheel nuts.
Tighten the inner wheel nuts of the
same wheel to the specified torque.
Next, tighten the outer wheel nuts to
the specified torque.
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326 Vehicle Care
{Warning
If you find any abnormal
conditions with the wheel nuts
such as frequent loosening of
retightened nuts, have your
vehicle checked or serviced at the
nearest dealer as soon as
possible.
Fully engage the wheel wrench on a
wheel nut in order to tighten the nut
to the specified torque. However, do
not use a pipe as a handle
extension or your foot to apply force
on the wrench. This would tighten
the nut more than required and
might damage components.
Both under-tightening and
over-tightening of wheel nuts may
cause broken wheel studs or
cracked disc wheels and could lead
to wheel detachment. Adhere to the
specified tightening torques.
When replacing a tire with a new
one, use only a tire of the same
type and size as the replaced tire;
otherwise, driving safety could be affected. Avoid mixed use of
different types or different size tires
at all costs.
If a Tire Goes Flat
When the tire goes flat while driving,
ease off the accelerator pedal, avoid
hard braking, hold on to the steering
wheel firmly, and stop the vehicle.
The tire should be changed in a
safe, open location to prevent
obstructing other vehicles or
pedestrians.
{Warning
If you continue to drive on a flat
tire, undue force will be applied to
the wheel studs, possibly causing
the studs to break and the wheel
to come off. You and others could
be seriously injured.
See “Tire Replacement
Recommendations” underWheels
and Tires 0308.
Jump Starting
Jump Starting - North
America
When the Battery is
Discharged
Use a jumper cable (sold
separately) and the battery of
another vehicle to start the engine in
the following sequence.
{Danger
Follow the precautions listed in
the jump starting instructions
when working on or near the
battery. Personal injury
(particularly to eyes) or property
damage may result from battery
explosion, battery fluid or
electrical (short circuit) burns.
If battery fluid should come in
contact with an eye, immediately
wash away using a large amount
of water and continue washing for
(Continued)
Chevrolet Low Cab Forward Owner Manual (GMNA-Localizing-U.S.-
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354 Service and Maintenance
How to check: This operation could
be difficult and you may choose to
have this done at your dealer
Service Department.
1. Turn the engine control switch to
the "ON" position (not to start the
engine), and press the brake pedal
several times.
2. Check for the noisy sound of the
electric vacuum pump inside the
instrument panel at the same time
as vacuum warning buzzer sound,
and check that the brake low
vacuum warning light comes on.
3. Then, after you start the engine,
the main vacuum pump driven by
the engine will start running. If the
electric vacuum pump operation
(noisy sound) and the vacuum
warning buzzer stop, and the brake
low vacuum warning light goes off
thereafter, the operation is normal.
4. If you cannot hear the noisy
sound of the electric vacuum pump,
check the electrical wiring and
repair as necessary. If it cannot be
repaired, replace the electric
vacuum pump.20. BRAKE FLUID :
Check the fluid
in the brake fluid reservoir every
12 000 km (7,500 miles) and replace
fluid every 48 000 km
(30,000 miles).
21. BRAKE LINE AND HOSES :
Check lines and hoses for proper
hook-up, binding, leaks, cracks,
chafing, etc. every 48 000 km
(30,000 miles). Any questionable
parts should be replaced or repaired
at once. When rubbing or wear is
noted on lines or hoses, the cause
must be corrected at once.
22. HYDRAULIC UNIT : Change
every 10 years.
23. DIFFERENTIAL GEAR OIL :
Replace lubricant every 48 000 km
(30,000 miles) or every 24 months.
Check lubricant level every
12 000 km (7,500 miles) or every
12 months, and add lubricant to
within 0 to 10 mm (0 to 0.4 inch) of
the bottom edge of the filler hole if
necessary. 24. POWER STEERING FLUID :
Replace power steering fluid every
24 months or 60 000 km
(37,500 miles), whichever occurs
first.
25. STEERING WHEEL FREE
PLAY :
Check steering wheel free
play after the first 1 040 km
(650 miles) and then every
10 400 km (6,500 miles).
Steering wheel free play
10-50 mm (0.39-1.97 in)
26. STEERING GEAR BOX
TORQUE : Retighten the fixing bolts
of the steering gear box to the
specified torque every 48 000 km
(30,000 miles). Specified tightening
torque.
Steering gear box tightening torque
102 Y(75 lb·ft)
27. DRIVESHAFT FLANGE
TORQUE : Check the fixing bolts of
driveshaft flange for looseness or
damage first 12 000 km
(7,500 miles). Retighten the fixing