Where Can You Find Air Brake System Diagrams for Tractor Trailers?

Bendix Spicer Foundation Brake LLC. has diagrams available with part names and model numbers for several different styles of air brake systems in their online manual titled "Air Brake Handbook."

Air brake systems all tend to be very similar. When air brakes are released, air flows from the air compressor to the governor which controls the air pressure in the reserve tanks. When the brake pedal is depressed, air is released from the circuit, and air pressure at the brake assembly drops. Each wheel or set of wheels has a brake assembly attached to it. It is composed of a brake chamber, slack adjuster, brake shoes and brake drums. The brake chamber contains a diaphragm that has air pressure on one side and springs on the other. When the parking brake is set, the air pressure is released from the system, and the springs force the diaphragm into the closed position. When the diaphragm is in the closed position, it puts pressure on the slack adjuster which forces the brake shoes against the brake drum. The friction created by the pressure of the brake shoes on the drum slows the vehicle. This system has been in use since being invented by George Westinghouse in 1869.