Maine CDL Permit Test - Air Brakes

The purpose of an Anti-Lock Braking System (ABS) is to prevent wheel lockup while brakes are being applied.

Friction inside a brake drum is caused when the brake shoes and linings push against the inside of the drum. The friction in the drums will slow and stop the vehicle.

Do not use the brake pedal when the spring brakes are on. This could damage the brakes by subjecting them to the combined forces of springs and air pressure.

Brakes are designed to take a lot of heat, but drivers should not rely solely on the brakes to slow their vehicle. Brakes may fade and lose their ability to slow down the vehicle if they become too hot, so drivers should also rely on the engine braking effect.

A vehicle's total stopping distance is made up of perception distance, reaction distance, brake lag distance, and braking distance. With all of these factors included, an air brake-equipped vehicle traveling at a speed of 55 mph under ideal driving conditions will need approximately 450 feet to come to a complete stop.

Compressed air usually contains a certain amount of moisture and compressor oil, which can build up in the air storage tanks and damage the brake system. The tanks should be drained to clean out these accumulations. On a tank with a manual drain valve, draining should be performed at the end of each day of driving.