In S-cam drum brakes, which component is shaped like the letter S?

• A. S-cam
• B. Brake pad
• C. Drum
• D. Slack adjuster

Answer: (A)

In this brake setup, the part that actually creates the outward push to press the shoes against the drum is the S-cam. It’s shaped like the letter S, and when the brake is applied, the cam rotates so its curved lobes push on the ends of the brake shoes, forcing them outward to contact the inside of the drum. That S-shaped profile is what gives it its name and unique action.

The drum itself is the rotating cylinder that the shoes squeeze against to slow or stop rotation. In drum brakes, the friction surfaces are the brake shoes with lining, not brake pads. The slack adjuster, meanwhile, is the mechanism that maintains the proper clearance between the shoes and the drum; it doesn’t have the S shape or the role of pushing the shoes outward.