[PDF] Air Brake Handbook Bendix Air Compressors. The air compressor is the source of energy for the air brake system. Usually driven by the vehicle engine, the air compr essor builds the air pressure for the air brake system. The air compressor is typically cooled by the engine coolant system and lubricated by the engine oil sup ply. Bendix Air Brake System Schematic | Brake | Valve Specify Genuine Bendix. Drain the front axle or secondary reservoir to 0 psi. The rear axle or primary reservoir should retain most of its pressure. On combination vehicles, the trailer air system should remain charged. C. Tractor and trailer brakes should not apply automatically. With no air