What is the function of the brake camshaft in S-cam drum brakes?

• A. It reduces air pressure
• B. It rotates to spread the brake shoes against the drum
• C. It monitors wheel speed
• D. It pulls the slack adjuster

Answer: (B)

In S-cam drum brakes, the brake camshaft’s job is to convert the push from the brake chamber into outward movement of the two brake shoes. When air pressure is applied, the push rod turns the cam. The S-shaped cam then rotates and its lobes push the ends of the shoes apart, spreading them against the drum to create friction and slow the wheel. This is the essential action that produces braking force. It isn’t about reducing air pressure, monitoring wheel speed, or pulling the slack adjuster—those are handled by other parts of the system.