Why is an S-cam drum brake called an S-cam?

• A. It is shaped like the letter 'S'.
• B. It was named after the engineer who designed it.
• C. It stands for Safety Cam.
• D. It is a type of servo cam.

Answer: (A)

The name comes from the cam itself. In an S-cam drum brake, the cam that’s driven by the brake linkage has an S-shaped profile. As the cam turns, the lobes along that S push the ends of the two brake shoes outward against the drum. That outward spreading is what creates the braking force, and the S shape makes the shoes move simultaneously and evenly from a single rotating element. So it’s called an S-cam because the cam’s geometry looks like the letter S, not because of any safety or servo designation or because of who designed it.