Air Brake Manual

Other factors that affect the braking ability of the
vehicle, include:
· overheated brakes;
· worn linings;
· oversize drums;
· malfunctioning valves;
· valves with above normal release pressure;
· seized or partially seized brake camshafts or shoe
anchors;
· excessive moisture in reservoirs;
· contaminated brake linings.
Brake failures are seldom the result of catastrophic
system failure. They are usually the result of brakes
being out of adjustment, often to the point that there
is no braking action on some wheels.
Under frequent braking conditions and depending
on the severity, there will be some expansion of the
brake drum because of heat and the amount will
vary with the thickness of the drum. This expansion
of the drum will also add to the overall push rod
travel.
The driver should be trained in brake adjustment
prior to attempting the practical examination.
Stroke vs. Force
The amount of force available at the push rod is
consistent out to two inches of stroke. After two
inches, push-rod force drops very quickly.
4000
Recommended max. stroke at
100 psi before readjustment
Push-rod Force (in lb) at 100 psi
3000
2000
1000
0
Air chamber
bottom-out
0 1/2 1 1 - 1/2 2 2 - 1/2 3
Don’t be Fooled - Check the Slack
Push-rod Stroke
(in inches)
It is up to you, the driver, to ensure that your vehicle
has safe, properly adjusted brakes.
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