Lesson 2/Learning Event 3
Next, follow the hydraulic line from the master cylinder to the air
hydraulic cylinder. Check for breaks, kinks, and leaking
connections. Inspect the airhydraulic cylinder mounting bolts for
tightness and the cylinder for dents. Check for leaks at all
Follow the hydraulic lines from the airhydraulic cylinder to the
tees at the front and rear axles and on to each wheel cylinder.
Check all lines for leaks, kinks, and cracks. Ensure the lines are
supported properly to the frame or axle. Check each flexible line
for leaks and frayed material.
Inspect the backing plate and lower drum area of each wheel for an
indication of brake fluid. Leaking wheel cylinders will leave traces
of fluid that can often be seen without pulling the wheel and brake
drum. This type of leak will soak the brake lining and cause a brake
to grab. While at the wheels, check each one for secure lugs and
Next check the air compressing system. Be sure the compressor is
mounted securely and the air breather is clean. Inspect drive belts
(where applicable) for proper tightness and condition. Worn, frayed,
or glazed belts can cause trouble. Check the condition of all air
lines and connections from the compressor to the governor, pressure
gage, buzzer system, air tanks, airhydraulic cylinder, and for
tightness at connections. Check the air tanks for secure mounting
and condition. Open the petcocks to be sure all moisture has been
drained and then close them again.
To determine exactly how well a brake system is operating, the
vehicle must have its trailer connected and be roadtested. This
includes the checks made prior to moving the vehicle, while the
vehicle is in motion, and after the road test is finished.
Start the engine and adjust the throttle so that it runs at about
1,000 RPM. While the engine is warming up, the following steps
should be performed:
Ensure the warning buzzer operates until the air pressure
builds up to about 60 PSI (105 PSI for M809series vehicles).
pressure builds up steadily.