Brake camshafts are specifically designed for heavy-duty vehicles like semi-trucks, tractors, and trailers. These applications demand robust and durable camshafts that can withstand the rigors of frequent braking and heavy loads. In the brake cylinder, the pressure builds until it is strong enough to push the cam. The cam then rotates, bringing up rollers that push the shoe out against the drum. The friction between the shoe lining and the drum slows the wheel.