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Brake System Maintenance
1. When crawling under the semitrailer is
necessary, chock all wheels of the trailer and
tractor. When jacking is necessary, chock all
wheels and support the semitrailer
undercarriage with jack stands sufficient to
withstand the weight of the semitrailer and
load. Failure to take adequate safety
measures may result in serious personal
injury or death.
2. Use great care if wheels or brake drums must
be handled. They may be very hot and can
cause serious burns.
General
A daily general inspection will reveal the most common
problems found in the spring brake system. This
inspection should include the following:
1. Check air hoses for chafing, bends, kinks, or
damaged fittings. Replace defective hoses.
2. Check the brake system for loose, missing,
deformed, or corroded fasteners. Replace and
tighten defective hardware.
3. Check brake linings for excessive wear or distortion.
4. Drain air reservoir daily. A drain cock on the bottom
of each air reservoir vents the tank to drain collected
water and oil. If held open, air pressure in the tanks is
relieved, causing the emergency or parking brakes to
be applied (See Figure 4-13.)
Figure 4-13: Drain Cock Locations
WARNING
DRAIN COCK PULL CORD
(ABOVE STREETSIDE
SUSPENSION HANGER)
MAINTENANCE AND LUBRICATION
Spring Air Brake Chambers
Check for faulty units. Check the condensation holes on
the underside of the brake chambers to make sure they
are open. The spring brake has two brake chambers, a
service chamber and an emergency chamber or spring
chamber. Service brake chambers should be
disassembled and cleaned at 50,000 miles or yearly. The
diaphragm and any marginal parts should be replaced.
When replacing the service diaphragm, replace the
corresponding parts for the other chamber on the same
axle (to aid in even brake application and release).
Examine yoke pin for wear and replace as necessary.
The spring chamber should not be serviced. Replace
entire unit (both service and spring chamber) if spring
chamber becomes faulty.
The spring brake chamber employs a spring with
high forces. service should not be attempted.
Serious injury or death may result.
WARNING
4-19
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