Monaco 2002 Diplomat, Service Manual

Page: 274 / 324

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 approximately 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 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.
NOTE: When the park brake is released the Park illumination
lamp will remain lit until air system pressure is above 65 psi.
WARNING: If the air tank is not dumped there is the pos-
sibility of an accidental release of the parking brake.
Traveling with small children and/or pets may require a
small block to be fabricated to prevent accidental release.
The block should be placed under the knob and rested on
the dash panel. A wooden clothes pin, clasped at the base of
the shaft, will work.
Chassis Information
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D I P L O M A T
1 0 • 2 7 4
BRAKE - PARK &
EMERGENCY
SYSTEMS