Actuation of trailer park (emergency) or tractor bobtail position
To actuate the trailer brakes only, pull out the trailer air supply knob (1).
The trailer brakes are now applied whether emergency or spring brakes
are used on the trailer.
This mode is also used when the tractor or truck with trailer is used
during bobtail operation.
ANTI-LOCK BRAKE SYSTEM (ABS)
Four-wheel anti-lock brake system (ABS)
A noise from the hydraulic pump motor and pulsation in the pedal may
be observed during ABS braking events. Pedal pulsation coupled with
noise while braking under panic conditions or on loose gravel, bumps,
wet or snowy roads is normal and indicates proper functioning of the
vehicle’s ABS. If the vehicle has continuous vibration or shudder in the
steering wheel while braking, the vehicle should be inspected by a
qualified service technician.
The ABS operates by detecting the
onset of wheel lockup during brake
applications and compensating for
this tendency. The wheels are
prevented from locking even when
the brakes are firmly applied. The
accompanying illustration depicts
the advantage of an ABS equipped
vehicle (on bottom) to a non-ABS
equipped vehicle (on top) during hard braking with loss of front braking
traction.
1
2
Driving
113
When the Traction Controlswitch, located on the instrument panel, is
in the off position, the traction control light will be illuminated.
If you should become stuck in snow or ice or on a very slippery road
surface, try switching the Traction Controlsystem off. This may allow
excess wheel spin to“dig”the vehicle out and enable a successful
“rocking”maneuver.
Aggressive driving in any road conditions can cause you to lose
control of your vehicle increasing the risk of severe personal
injury or property damage. The occurrence of a Traction Control
event is an indication that at least some of the tires have exceeded
their ability to grip the road; this may lead to an increased risk of loss
of vehicle control, vehicle rollover, personal injury and death. If you
experience a severe road event, SLOW DOWN.
AIR SUSPENSION (IF EQUIPPED)
Note:The vehicle must not be operated without air in the suspension
springs. Operating the vehicle without air in the air suspension springs
will damage the suspension, degrade ride performance and may cause
property damage.
The suspension system automatically adjusts to different loads to
maintain a constant frame height. The system allows for ease of vehicle
loading and provides improved vehicle ride and increased driver comfort.
Air suspension dump switch (if equipped)
The system is controlled by a switch
located on the instrument panel.
The switch will operate only when
the ignition is in the ACC
(Accessory) or IGNITION positions
and the air tanks have sufficient
pressure to fill the air springs. When
the ignition is turned off, the
suspension will remain in whatever
state it was last set.
Note:The suspension will dump air when the ignition is in the ACC or
IGNITION position, but will only fill when the ignition is in the IGNITION
position.
When the upper portion of the switch is pressed and the vehicle speed is
below 5 mph (8 km/h), air supplied to the air spring is exhausted,
Driving
115
lowering the frame for loading. Pressing the lower portion of the switch
causes air to fill the air springs so the vehicle will remain normal ride
height.
Tractor-trailer connections
To reduce the risk of personal injury, use extreme caution when
making brake and light connections. Inclement weather and
accumulated road contamination deposits on handhold and stepping
surfaces require extra care to avoid slip and falls. Provide adequate
lighting of working areas.
Do not climb on the back of the tractor unless it has been
provided with a deck plate and handholds. Use a three-point
stance when climbing up and down from a deck plate. Do not jump
from the vehicle. Whenever possible, make all connections while
standing on the ground.
Connecting and disconnecting a trailer with air suspension
When connecting to a trailer:
•Press the lower portion of the switch and air will exhaust from the air
suspension system.
•After making the connection to the trailer, press the upper portion of
the switch, then raise the landing gear.
When disconnecting the trailer:
•Lower the landing gear, then press the lower portion of the switch.
•Disconnect the brake hoses, trailer-side and rear light connectors,
then pull the release lever on the fifth wheel.
The upper portion of the switch must be pressed before operating with a
trailer or operating in the bobtail mode.
Suspension conversions
It is not recommended, or approved, that suspension conversions be
performed. However, it is understood that, on occasion, aftermarket
add-on suspensions are installed by others on the truck chassis which
allow operator control for weight transfer from other axles (i.e., air lift
axles).
Driving
116
When operating a loaded vehicle, the driver must keep all
adjustable axles on the ground at all times, supporting their
share of the vehicle’s load. Failure to do so can overload other axles,
tires, wheels, springs, steering components, brakes and frames,
resulting in early component failure, loss of vehicle control, possible
property damage and personal injury.
FIFTH WHEEL OPERATION
Failure to follow the fifth wheel manufacturer’s instructions for
hooking and unhooking as well as sliding the fifth wheel could
result in an accident, personal injury or death.
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.
Hook-up
1. Fifth wheel jaws must be fully opened.
2. Tilt the fifth wheel back to prevent body damage when the tractor is
backed under a trailer.
3. Block the trailer wheels and be sure the trailer spring brakes are
adjusted and applied. Never chase a trailer.
4. Make sure the brake hoses and light cords are clear of the fifth wheel.
5. Back the tractor squarely under the trailer, engaging the fifth wheel
jaws on the kingpin. Always back-up slowly, making sure the trailer is
neither too high nor too low. Avoid backing under the trailer from an
angle.
6. Connect the service and emergency brake hoses and trailer light
connector. Refer toTractor-trailer connectionin this chapter, adhering
to the warning and using the three-point stance while connecting and
disconnecting the trailer.
7. 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.
8. Be sure the coupler release lever is in the locked position.
Driving
117
9. Charge the trailer brake system. Set the trailer brakes, either with the
hand valve or tractor protection valve. Pull against the trailer for an
additional check of proper hook-up. Do not pull hard enough to damage
or strain the equipment.
10. Set the tractor parking brakes and fully raise the trailer landing gear.
Refer toBrakesin this chapter for proper operation of the parking brake
and trailer brakes.
11. 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.
AUTOMATIC TRANSMISSION OPERATION (IF EQUIPPED)
Main transmission, auxiliary transmission, transfer case and power
take-off (PTO) control shift patterns can be found on a placard or decal
on the driver’s sun visor, on the instrument panel or on the shift control
itself.
The main transmission control is used to select the various gear ratios or
speeds of the transmission. Selecting D (Direct Drive), does not change
the transmission gear ratio, but is used where the gear ratios in the main
transmission are adequate to handle the vehicle operation.
Hold the brake pedal down while you move the gearshift lever
between positions. If you don’t hold the brake pedal down, your
vehicle may move unexpectedly and cause property damage, personal
injury or death.
Allison 2000 automatic transmission
This transmission is available with a column-mounted gearshift lever. The
gear positions are displayed on the RNDL in the instrument cluster.
Driving
118
The PTO gear is in constant mesh with the drive gear in the torque
converter housing. A friction clutch or constant drive is used to transmit
power to the PTO.
CLUTCH (IF EQUIPPED)
Properly maintain the clutch to prolong it’s life. Do not ride or slip the
clutch as this will cause unnecessary heat and wear.
Clutch precautions
Maintain specified clutch adjustment; regularly inspect the clutch control
linkage for tightness.
When adjustment of the clutch is necessary, it is very important that the
work be performed properly or early clutch failure may result and a
costly clutch overhaul may become necessary. Clutch work should only
be performed by a qualified technician.
Engaging the clutch
•Always start in the proper gear.An empty vehicle can start in a
higher gear than a fully loaded vehicle. Starting in too high a gear can
cause clutch slippage and excessive heat and wear on the clutch. A
gear that will start the vehicle moving at idle speed is the correct gear.
If the engine has to be revved to get the vehicle going, the gear
selection is too high.
•Do not shift until the vehicle has reached the proper speed.
Upshifting before the vehicle has reached the proper speed can cause
clutch slippage and excessive heat and wear on the clutch.
•Never hold a vehicle on a grade with the clutch.This will cause
the clutch to slip and can actually burn up the clutch.
•Never coast with the clutch disengaged.The high RPM
(sometimes over 10,000), can actually burst the facing material of the
clutch.
•Never engage the clutch while coasting.Re-engaging the clutch
after coasting may not only cause a great shock to the clutch, but the
whole drivetrain. Internal engine damage and/or clutch and flywheel
failure can result from this.
If your vehicle’s transmission is equipped with a ceramic clutch, you
must start the vehicle moving in first gear and engage the clutch before
pressing the accelerator at idle. Also, don’t try to slip the clutch by
raising engine RPM and riding or feathering the clutch pedal since the
vehicle will experience erratic engagement. Erratic engagement can
cause the engine stalling and potential serious damage to the vehicle’s
driveline components.
Driving
122
To go forward
With the engine idling, depress the
clutch pedal and push the range
control button to the LO range
position. Shift into the LO gear
position and engage the clutch while
pressing on the accelerator to start
forward. Operate the clutch and
upshift through the pattern as
required by driving conditions. To
shift into the HI range from 5th gear
(LO range), place the range control
in the HI range position, then shift into 6th gear. When downshifting
from HI to LO, place the range control into the LO range, then downshift
from 6th gear to 5th gear (below 1,500 engine RPM).
To go backward
Reverse is obtained by putting the
gearshift lever in R (Reverse) and
the range control button in LO or
HI.
Power-take off operation (PTO) with a manual transmission
Transmission-mounted power take-off units are available for local
installation on your vehicle. See your Body Builder’s Layout Book for
restrictions on use and installation of power take-off units.
To engage the PTO unit, stop the vehicle and place the transmission
control in neutral. Depress the clutch and allow the gears to stop
rotating, then engage the PTO unit. The PTO can also be selected with
the transmission in gear as long as the clutch is depressed.
When operating the PTO unit with the vehicle stationary, first set the
parking brake (chock the wheels if the vehicle is on a hill or other
unlevel surface).
7
29
4
8
3 6
1
10
5
R
Neutral
Driving
129
REAR AXLE INFORMATION
Axle operating temperature normally will not exceed 100°F (38°C). If
the operating temperature exceeds 230°F (110°C), the rate of axle
lubrication oxidation will increase and shorten the life of the lubricant
and seals, requiring axle lubrication changes to become more frequent to
preserve the axle. Extreme Pressure (EP) lubricants should not be run
consistently above 230°F (110°C).
Gross axle weight
Your truck has gross axle weight, gross vehicle weight and gross
combination weight ratings. Do not exceed these ratings.
Exceeding these ratings by overloading can cause component
failure resulting in property damage, personal injury or death.
Rear axles with locking or limited-slip differentials
If your vehicle is equipped with a locking or limited-slip differential, note
the following:
•Power will be transmitted to the opposite wheel should one of the
wheels begin to slip.
•Both wheels must be raised free of the ground should it be necessary
to operate one wheel with the vehicle stationary.
If both wheels are not raised free of the ground, the one wheel
that is not raised may pull the vehicle off its support, possibly
resulting in personal injury
Driver-controlled differential lock
To prevent the vehicle from moving when servicing the wheels, tires or
brakes, turn the engine off and raise all drive wheels of the locker
differential axle. Axles equipped with NoSPIN Detroit Locker differentials
deliver power to both wheels even when only one wheel is on the
ground.
Failure to raise all drive wheels with this type of differential
could cause the vehicle to move unexpectedly, resulting in
property damage, personal injury or death.
Care should be taken to avoid sudden accelerations when both drive
wheels are on a slippery surface.
Driving
130