Note:
Read and understand the following
steps and perform them whenever you
prepare to drive the vehicle.
Note: The parking brake does not disengage
unless sufficient system air pressure is
available.
1. Press and hold the service brake pedal
while the engine is running.
2. Select the appropriate drive gear.
3. Push and hold the yellow dash-mounted parking brake knob until
the parking brake light turns off, then
release.
Parking Brake Light Illumination due
to Low Air Pressure
If the air pressure becomes too low at any
time during vehicle operation, the parking
brake may apply and the parking brake
light turns on.
If the parking brake applies due to low air
pressure, immediate service is required to
the parking brake system.
Parking Brake Warning System
If the parking brake light blinks and a tone
sounds when pulling the yellow control
knob out, this indicates the parking brake
is not functioning properly. Seek service for
the parking brake immediately.
With the ignition key not in the run position:
• A tone sounds if the parking brake
remains released (or in an unknown
state). The tone stops after
approximately 8 minutes or until the
parking brake is applied. Seek service
for the parking brake immediately. Diesel engines: Parking brake light
operation (the light only works when the
ignition key is in the run position):
• On:
Parking brake applied.
• Off:
Parking brake released and no
faults or malfunctions detected.
• Blink and tone:
Parking brake
released (or in an unknown state) and
faults or malfunctions detected.
Releasing Spring Manually WARNINGS
Do not attempt to disassemble the
parking brake chamber under any
circumstances. The high spring load
may cause serious injury. Block the wheels to help prevent the
vehicle from moving.
Unexpected and possibly sudden
vehicle movement may occur if these
precautions are not taken.
If you release hydraulic pressure from the
spring brake chamber the power spring
applies the brake and, unless hydraulic
pressure can be re-established, you must
release the spring brake as follows in order
to move your vehicle.
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Loosen the jam nut (A) and un-thread the
adjustment rod (B) from the chamber to
reduce tension on the cable (C). Continue
to un-thread the adjustment rod all the
way and remove it from the chamber.
Air Brakes
WARNING
This control is used for parking only.
Do not leave the vehicle unattended
after setting the parking brake
without placing the transmission park (P).
Use of wheel chocks is also recommended
in hilly or off-road usage. If the service brakes should fail to operate
while your vehicle is moving, you can make
an emergency stop with the parking brake.
Since the parking brake only applies
stopping power to the rear wheels, your
vehicle
’s stopping distance greatly
increases and the handling of your vehicle
is adversely affected. Make repairs
immediately to an inoperative air brake
system circuit. Pull the yellow parking brake knob out to
apply the parking brake. Push the knob in
to release the parking brake.
The parking brake light
illuminates and remains
illuminated (when you switch
the ignition to the on position) until you
release the parking brake. Releasing Spring Brake with Air
Pressure
The air system in all vehicles with
spring-actuated rear wheel parking brakes
is equipped with a valve located on the
governor for connection to an outside air
supply. The valve lets you recharge the
system with air from an outside source,
releasing the spring-actuated parking
brakes. Your vehicle is now ready to tow in
an emergency.
You can only use an outside air source if
the protected system is in operating
condition. If you cannot restore air pressure
in the protected air system, you must
release the spring-actuated brakes
manually.
Releasing Spring Manually
WARNINGS
Do not attempt to disassemble the
parking brake chamber under any
circumstances. The high spring load
may cause serious injury if the chamber
clamps are removed. Block the wheels to help prevent the
vehicle from moving.
Unexpected and possibly sudden
vehicle movement may occur if these
precautions are not taken.
If you release air pressure from the spring
brake chamber, the power spring applies
the brake and, unless air pressure can be
re-established, you must release the spring
brake as follows in order to move your
vehicle.
Do not use impact wrenches as they may
damage the piston and prevent proper
caging of the spring. Do not apply more
than 50 lb.ft (68 Nm) to the release bolt
nut.
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TRAILER BRAKES
Trailer Brake Hand Control (If Equipped)
WARNING
The hand control should never be
used to apply the brakes when the
tractor and trailer are parked
unattended. Air may leak from the system
and the vehicle could possibly move,
resulting in possible property damage,
personal injury or death. The hand control is located on the
right-hand side of the instrument panel. It
applies the trailer service brakes, which are
independent of the truck or tractor service
brakes.
It operates a valve that provides gradual
control of air pressure applied. When the
valve is only partially applied, you can
override the trailer brakes by pressing fully
on the brake pedal.
To apply the trailer brakes using the hand
control, move the lever downward. The
further you push the lever down, the
greater the air pressure is applied to the
brakes. The lever remains in place until
manually moved. To release the trailer brakes, move the
lever up completely.
Trailer Air Supply and Parking
Brake Modular Controls (If Equipped)
The trailer air supply valve delivers air to
the trailer supply and automatically pops
out, shutting off the trailer supply, if
pressure decreases to approximately 35 psi
(249 kPa)
.
The parking brake controls the spring
brakes on the tractor. When you pull the
knob out, it causes the trailer supply valve
to pop out, applying both the tractor and
trailer parking brakes. You can
independently release the trailer brakes by
pushing only the trailer air supply valve in.
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A
B
12
A320
A E210341
Initial Charge
With the air system completely discharged,
both knobs (A and B) are out. When the
air pressure reaches 70 psi (4.83 bar), the
trailer air supply (A - red knob) may be
pushed in and should stay in, charging the
trailer air system and releasing the trailer
brakes. You can push in the parking brake (B -
yellow knob) and supply air to the tractor
spring brakes, releasing them.
Normal Driving Position
Push in both knobs (A and B) to supply air
to both trailer and tractor spring brakes,
releasing all brakes.
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System Park
With both knobs (A and B) pushed in
(normal driving position), the parking
brakes for both the tractor and trailer can
be applied by pulling the parking brake
knob (B) out, exhausting air from the
tractor spring brakes, simultaneously
causing the trailer air supply valve to pop
out, applying the trailer brakes.
Trailer Charge
If both knobs (A and B) are out, and you
want to recharge the trailer while leaving
the tractor spring brakes applied, the trailer
air supply (A) can be pushed in to recharge
the trailer air supply line. You can also use
this mode to park a combination vehicle
with tractor spring brakes.
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Automatic Application
If both knobs (A and B) are pushed in and
the brake system air pressure is reduced
to approximately 35 psi (249 kPa), the
trailer air supply (A) knob automatically
pops out applying the emergency or
parking brakes on the trailer. If the trailer
air supply (A) knob is manually held in and
the air pressure is reduced to
approximately
30 psi (207 kPa), a tripper
piston within the valve moves, exhausting
the trailer air supply, applying the trailer
brakes. Further reduction of air pressure,
while holding the trailer air supply knob in,
causes the parking brake knob to pop out
at
25 psi (172 kPa).
Actuation of Trailer Park (Emergency)
or Tractor Bobtail Position To actuate the trailer brakes only, pull out
the trailer air supply (A) knob. This applies
the trailer brakes whether the trailer uses
emergency or spring brakes.
You can also use this mode when the
tractor or truck with trailer is used during
bobtail operation.
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•
Shift to a lower gear when driving down
a long or steep hill. Do not apply the
brakes continuously, as they may
overheat and become less effective.
• If your transmission is equipped with
the Tow/Haul feature, use this feature
when towing. This provides engine
braking and helps eliminate excessive
transmission shifting for optimum fuel
economy and transmission cooling.
• Allow more distance for stopping with
a trailer attached. Anticipate stops and
brake gradually.
TRANSPORTING THE VEHICLE WARNING
To reduce the risk of personal injury
or property damage when manually
releasing the spring brakes, be sure
to block the wheels so the vehicle cannot
move once the brakes are released. Note:
Make sure to connect your vehicle
securely to the tow vehicle and that the tow
vehicle ’s parking brakes are set before
releasing the disabled vehicle ’s spring
brakes.
Before moving the disabled vehicle, check
for adequate road clearance of vehicle
components. If possible, unload the
disabled vehicle before towing. This
reduces any abnormal load to the vehicle
components resulting from the towing
procedures. Before towing, make sure to
release the parking brake fully. You can
reset the spring-actuated type parking
brake by recharging the air system with at
least 64 psi (441 kPa) of air. If the brake
system does not retain air pressure, then
you must release the spring brakes
manually. See
Parking Brake (page 121). Towing the Vehicle with the Front
Wheels Suspended
Note:
To avoid transmission damage, do
not tow your vehicle even a short distance
without suspending rear wheels or removing
the axle shafts or driveshaft.
Note: When towing a vehicle equipped with
a tandem axle from the front, raise the
forward rear axle so it can clear the road
surface and secure it to the frame with
chains or U-bolts, allowing only the rear rear
axle to contact the road surface. Remove
axle shafts from the rear rear axle assembly.
Cover the wheel hub ends to prevent loss
of axle lubricant and entrance of
contaminants. Use extreme care in securing
the chains or U-bolts to avoid possible
damage to the brake lines, hoses or other
components.
When it is necessary to tow a vehicle with
the front wheels suspended, take extra
precautions to avoid transmission or
differential damage:
• Remove the axle shafts from the axle
assembly to prevent the wheels from
driving the differential and the
transmission.
• Cover the wheel hub ends to prevent
loss of axle lubricant and entrance of
other contaminants. If you do not
remove the axle shafts, removal of the
driveshaft is required.
Towing the Vehicle with the Rear
Wheels Suspended
Note: To avoid damage to the cab roof or
air deflector when towing your vehicle
backward (rear wheels suspended), remove
the air deflector.
Whenever possible, it is preferable to tow
a disabled vehicle from the rear by raising
the rear of the chassis. When towing a
vehicle with the rear of the chassis
suspended, you must lock the front wheels
in the straight-ahead position.
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WARNINGS
When the tractor and trailer are
parked unattended, the trailer brake
hand control should never be used
to apply the brake, since air may leak from
the system, allowing vehicle movement,
resulting in possible property damage,
personal injury or death. Before hook-up, make sure:
•
The fifth wheel jaws are fully open.
• The fifth wheel is fully tilted back to
prevent body damage when the tractor
is backed under a trailer.
• You block the trailer wheels and adjust
and apply the trailer spring brakes.
Never chase a trailer.
• The brake hoses and light cords are
clear of the fifth wheel.
Hook-up
1. Back the tractor squarely under the trailer, engaging the fifth-wheel jaws
on the kingpin. Always back up slowly;
make sure the trailer is neither too high
nor too low. Avoid backing under the
trailer from an angle.
2. Connect the service and emergency brake hoses and trailer light connector.
3. Inspect the jaws of the fifth wheel to be sure they have fully closed on the
trailer kingpin and the trailer plate is
resting securely on the fifth wheel.
4. Make sure the coupler release lever is in the locked position.
5. Charge the trailer brake system. Set the trailer brakes, with either the hand
valve or tractor protection valve. Pull
against the trailer for an extra check of
proper hook-up. Do not pull hard
enough to damage or strain the
equipment.
6. Set the tractor parking brakes and fully
raise the trailer landing gear. 7.
Check the operation of all trailer lights
and correct any lights that may be
faulty.
Un-hook
1. Try to keep the tractor and trailer in a straight line.
2. Apply the parking brakes.
3. Lower the trailer landing gear, making sure it is on solid, level ground. The
weight of the trailer is to be on the
landing gear.
4. Block the trailer wheels.
5. Disconnect the brake hoses and light cords. Be sure hoses and cords are
clear.
6. Pull coupler release lever to disengage
the fifth wheel jaws.
7. Release the tractor parking brakes.
8. Pull out from the trailer slowly, allowing
the landing gear to take the load
gradually.
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