Final answer:
S-cam drum brakes are named after the S-shaped cam in each brake chamber, which converts linear force into rotational force to engage the brake shoes against the drum.
Step-by-step explanation:
S-cam drum brakes are called as such because they utilize an S-shaped cam in each brake chamber.
The cam is shaped like an 'S' and is responsible for converting the linear force from the brake air chamber into rotational force to engage the brake shoes against the brake drum.
The S-cam design is commonly used in heavy-duty vehicles and provides efficient braking performance.