An air brake chamber converts compressed air energy into mechanical force to stop heavy trucks and buses. The chamber contains a flexible rubber diaphragm and a heavy return spring. When you step on the brake pedal, compressed air enters the chamber, pushing the diaphragm forward. This drives a steel pushrod outward, which rotates the slack adjuster and turns the brake camshaft to press the brake shoes against the drum.
These chambers also serve a critical safety role as parking brakes. Spring brake chambers contain a second, high-tension spring held compressed by air pressure. If the truck loses air pressure, the spring snaps forward, applying the emergency brakes. Never attempt to disassemble a spring brake chamber. The internal spring is under thousands of pounds of pressure and can launch the metal cover with fatal force.