In an air brake system, the S-cam serves what purpose?

In an air brake system, the S-cam serves what purpose?

• A. It measures brake chamber air pressure
• B. It forces the brake shoes to the drums
• C. It compresses the brake fluid
• D. It releases the parking brake

Answer: (B)

The S-cam’s job is to convert the air pressure from the brake chamber into the outward force that pushes the brake shoes against the drum. When you apply the brakes, air fills the brake chamber and moves a piston or diaphragm that rotates the S-cam shaft. The curved lobes of the S-cam grip the ends of the brake shoes and turn, forcing the shoes to spread outward and press against the drum. This contact creates friction, which slows and stops the wheel. The S-cam remains in that extended position as long as air pressure is maintained, and the shoes retract when pressure is released by the system’s springs or valves. The other options aren’t what the S-cam does: measuring brake chamber air pressure is handled by sensors/gauges, not the cam; compressing brake fluid isn’t part of air brakes since they use air, not hydraulic fluid; and releasing the parking brake involves a separate mechanism, not the S-cam.

The S-cam’s job is to convert the air pressure from the brake chamber into the outward force that pushes the brake shoes against the drum. When you apply the brakes, air fills the brake chamber and moves a piston or diaphragm that rotates the S-cam shaft. The curved lobes of the S-cam grip the ends of the brake shoes and turn, forcing the shoes to spread outward and press against the drum. This contact creates friction, which slows and stops the wheel. The S-cam remains in that extended position as long as air pressure is maintained, and the shoes retract when pressure is released by the system’s springs or valves.

The other options aren’t what the S-cam does: measuring brake chamber air pressure is handled by sensors/gauges, not the cam; compressing brake fluid isn’t part of air brakes since they use air, not hydraulic fluid; and releasing the parking brake involves a separate mechanism, not the S-cam.