dump valve deflates the air springs to lower the rear
of the vehicle. When the switch is moved back to the
normal position, the suspension will return to the cor-
rect ride height. A guard is positioned around the
switch to minimize accidental activation. See
Fig. 5.10.
NOTICE
Do not operate the vehicle over uneven ground
such as ramps, speed bumps, curbs, etc. with
the air springs deflated. Doing this may lead to
air bag separation from the piston, preventing the
suspension air springs from reinflating.
NOTICE
Never exhaust air from the suspension while
driving. When the air is exhausted, the suspen-
sion will not absorb road shocks, and compo-
nents may be damaged.
Interaxle Differential Lockout Control
NOTICE
The interaxle lock should only be engaged when
the vehicle is moving slowly at low throttle. En-
gagement at high speed or power can damage
the axle(s).
The interaxle lock, standard on all dual-drive ve-
hicles, is driver-actuated by means of a LOCK/
UNLOCK control valve switch mounted on the control
panel. See
Fig. 5.10. A red indicator light comes on
whenever the interaxle differential is locked out
(switch is in the lock position; no differential action
between the drive axles). A guard around the switch
minimizes accidental activation.
Fifth Wheel Air Slide Control
NOTICE
Do not activate the fifth wheel slide control valve
while the vehicle is in motion. To do so could
cause damage to the fifth wheel member, the
kingpin, the cab or trailer, and ultimately to the
drivetrain.
The fifth wheel air slide valve permits repositioning of
the sliding fifth wheel from inside the cab. Moving the
air slide control valve switch to the lock position de-
activates the control valve and locks the fifth wheel
to the baseplate. See
Fig. 5.10. Moving the switch to
the unlock position activates the control valve and
unlocks the fifth wheel slide mechanism, allowing
changes to the total length of the tractor-trailer and
changes to axle loads to comply with varying state or
provincial laws. A red indicator light, if so equipped,
is illuminated whenever the fifth wheel slide is un-
locked. A guard is positioned around the switch to
minimize accidental activation.
Controlled Traction Differential Control
A controlled traction differential feature is included or
available as an option on some rear axles. A control
valve switch engages and disengages the controlled
traction feature to cause the axle shafts to rotate to-
gether. See
Fig. 5.10. The controlled traction, or dif-
ferential lock, should only be engaged when the ve-
hicle is moving slowly at low throttle to avoid causing
internal axle damage. The differential lock must only
be used for adverse road conditions. The use of the
lock increases the turning radius and affects the ve-
hicle handling. A guard is positioned around the
switch to minimize accidental activation.
Dash-Mounted Brake Controls
Parking Brake Control Valve and
Trailer Air Supply Valve
NOTICE
Do not step on the service brake pedal while the
parking brakes are applied. To do so can cause
damage to the brake mechanisms.
The yellow diamond-shaped knob operates the park-
ing brake valve. Pulling the knob applies both the
tractor and the trailer spring parking brakes. See
Fig.
5.11
. Pushing the knob in releases the tractor spring
parking brakes. Before the spring parking brakes can
be released, the air pressure in either air brake sys-
tem must be at least 65 psi (447 kPa).
The red octagonal-shaped knob operates the trailer
air supply valve. See
Fig. 5.11. After the vehicle and
its air hoses are connected to a trailer and the pres-
sure in the air system is at least 65 psi (447 kPa),
the trailer air supply valve knob must be pushed in
(and should stay in) to charge the trailer air supply
system and release the trailer spring parking brakes.
Driver Controls
5.7
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