Park & Emergency Brake Systems - Holiday Navigator 2003 Owner's Manual

Chassis Information
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Park & Emergency
Brake Systems
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A simple mechanical explanation of what occurs when a brake application
is made is as follows: The air system supplies air to the foot brake, this is
called a treadle valve. Pushing down on the treadle valve supplies an air
charge signal to a brake chamber. This sealed chamber consists of a spring and
air bladder. The air charge signal pushes on the bladder which extends a
threaded rod connected to the automatic slack adjuster. The slack adjuster
rotates the S-cam expanding the shoes against the drum. Air disc brakes follow
much the same principal, with the exception of the S-cams.
The park and emergency brake systems are combined and apply to the rear
drive axle only. These are called spring brakes. When the park brake is
applied, air is released from the rear brake chambers allowing the large spring
in each rear brake chamber to manually push against the automatic slack
adjuster. This rotates the S-cam applying the brake shoes against the drum.
The air system must be charged above 35 psi so the park brake will remain
released. Pushing down on the park brake handle charges the rear brake
chambers with air pressure, overriding the emergency brake springs and
releasing the brakes. In the event of air loss, while the vehicle is under
operation, the park brake will automatically apply (this occurs at approximately
30 psi) acting as an automatic emergency brake system.
When preparing to depart, allow the air system to achieve full air pressure.
This is indicated by the air gauge needles. Listen for the air dryer to purge,
indicating full air pressure has been obtained and the air dryer is functioning.
Look and listen for any abnormalities. Abnormal air pressure readings by
either needle of the air gauge should alert the operator. Have the air system
checked to avoid an untimely failure.
Should a failure occur in the air system, preventing the air pressure from
building, it may become necessary to "cage" the spring brakes. This is an
emergency procedure only. Caging the rear air brake chambers manually
overrides the spring brakes and allows the vehicle to move. This procedure
does not affect normal service braking. The brake disabling procedure is located
in Section 2 - Driving & Safety.
NOTE: When the park brake is released the Park illumination lamp
will remain lit until air system pressure is above 65 psi.
WARNING: When parked, if the air tank is not depleted there is the
possibility of an accidental release of the parking brake. Traveling
with small children and/or pets may require a small block to be fabri-
cated to prevent accidental release. The block should be placed under
the knob on the dash panel. A wooden clothes pin, clasped at the base
of the shaft, will work.
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