Page 158 - Driving Commercial Vehicles Manual+

chapter 8 — air brakes

Force multipliers

The force generated at the wheel to stop is a lot more than the force you
apply when pushing down on the brake pedal.

The driver is using a tool to
gain leverage to measure
the brake chamber pushrod
travel.

In this diagram, the driver is pulling on an air brake slack adjuster to measure
if the brake is within adjustment tolerance.
The slack adjuster, besides adjusting for brake wear, acts as a lever. Leverage
is a form of force multiplication.
Trucks and buses are much heavier than cars, so they need even more
mechanical advantage.

Air brake chamber components

Diagram of a typical clamp-
type air brake chamber.

The diagram above shows the most common device used to apply truck air
brakes — the air brake chamber. It converts the force of compressed air into
a strong mechanical force through the pushrod and slack adjuster.

The air brake chamber consists of a flexible diaphragm clamped between
two steel housings. The diaphragm construction is similar to a tire sidewall,
consisting of a reinforced fabric core with a rubber coating. Other main parts
are the pushrod and plate assembly, and a return spring.

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