Arizona Air Brakes CDL Practice Test

What typically holds back the spring brakes during normal driving conditions?

1. Spring pressure

2. Bolts or clamps

3. Centrifugal force

4. Air pressure

The correct answer is: Air pressure

During normal driving conditions, air pressure is what holds back the spring brakes. The air brake system relies on compressed air maintained in the brake chambers to keep the spring brakes released and functioning properly. When the driver applies the brakes, the air pressure decreases, allowing the spring brakes to engage. This is crucial because in the event of a loss of air pressure—like a brake failure or air leak—the spring brakes will engage automatically. Hence, the system is designed with air pressure as the primary means of controlling the brake application under normal operations. Understanding this mechanism is vital for drivers, as it emphasizes the importance of maintaining proper air pressure in the system to ensure safe and effective braking.