Illinois CDL Practice Exam

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How do S-cam brakes function in an air braking system?

  1. By pumping air into each brake chamber

  2. By rotating the foundation brakes

  3. By twisting the brake camshaft using air pressure

  4. By manually engaging the brake shoes

The correct answer is: By twisting the brake camshaft using air pressure

S-cam brakes work by utilizing a camshaft that rotates in response to air pressure. When the driver applies the brakes, air pressure is sent to the brake chambers. This pressure acts on a diaphragm in each brake chamber, which then pushes the rod connected to the S-cam. The S-cam rotates, pushing the brake shoes against the brake drum with a wedging action. This ensures effective braking by increasing the surface area contact between the brake shoes and the drum as the cam shaft twists, ultimately slowing down or stopping the vehicle. Understanding the function of S-cam brakes is crucial for maintaining safety and efficiency in air braking systems, especially in larger vehicles like trucks and buses. This mechanism is preferred for its effectiveness in high-pressure applications, as it provides responsive and reliable braking capabilities.

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