Navistar WorkStar Series, Operator'S Manual

Page: 162 / 258

Operation
WARNING
Always chock the wheels when manually
releasing the spring brakes, or the vehicle could
roll causing property damage, personal injury, or
death.
For towing, make sure the vehicle is securely
connected to tow vehicle and tow vehicle parking
brakes are applied before releasing the disabled
vehicle’s spring brakes.
All vehicles with air brakes are equipped with spring brake
chambers for parking. The parking system is operated manually
by a single valve, which in the case of a tractor also controls the
parking system on the trailer.
The purpose of this brake is to hold the vehicle in a parked
position and to assist in bringing it to an emergency stop. The
parking brake should not be used to brake the vehicle during
normal driving.
To apply the parking brake, pull out control. To release the
parking brake, push in control.
On single-unit trucks and tractors with independent parking
and trailer controls: if air pressure is reduced to approximately
20 to 45 psi (138 to 310 kPa) in both the primary and secondary
systems, the parking brakes will automatically apply.
On tractors with the modular control system: if air pressure is
reduced to approximately 20 to 45 psi (138 to 310 kPa) in both
the primary and secondary systems, the parking brake control
will automatically apply. For the exact air pressure set points,
refer to the Service Manual.
It should be noted that upon loss of air pressure, partial spring
brake application will occur prior to automatic application of the
control valve.
To release, recharge system to 70 psi (483 kPa) and push in the
parking brake control. If the system cannot be recharged and
the vehicle must be moved, the spring brake must be manually
released (caged).
In the event it is necessary to move the vehicle after an
emergency application (before air pressure can be restored),
the parking spring can be compressed mechanically to release
the brake. A release stud spring caging tool is furnished with
the brake chamber assembly. The release stud engages in the
spring pressure plate and its nut is tightened to compress and
cage the spring and release the brake.
Remove release stud assembly from carrying pocket.
Apply a light coat of antiseize compound to the threads of the
release stud to avoid any unnecessary wear of the threads.
Remove the access plug from the end of the spring chamber.
Insert the release stud through the opening in the chamber and
into the spring pressure plate.
Turn the release stud one-quarter turn to engage the tangs on
the release stud into the slot in the pressure plate. Install the nut
on the release stud. Be sure tang on release stud stays engaged
with slot on pressure plate while installing the nut. Tighten the
nut with a wrench to compress the spring.
Parking Brake Reset
Charge spring brake chambers with air pressure. Loosen nut
and remove the release stud and nut from the spring housing and
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