Which statement best describes the role of the spring brakes?

Which statement best describes the role of the spring brakes?

• A. They require hydraulic assistance to function
• B. They engage automatically when air pressure becomes too low to hold the vehicle
• C. They are used only on icy roads
• D. They replace the service brakes at all times

Answer: (B)

Spring brakes act as the automatic hold and emergency mechanism in an air brake system. When air pressure drops to a low level, the springs push the brake shoes against the drums, automatically applying the brakes to hold or stop the vehicle. This is why the statement describing automatic engagement as air pressure becomes too low to hold the vehicle is the best description. Under normal operation, the driver uses the service brakes, which are actively controlled by air pressure for everyday stopping. The springs are not a hydraulic system, they don’t replace the service brakes at all times, and they aren’t limited to icy road conditions.