Michigan CDL - Air Brakes Practice Exam

What should a driver check to ensure safe operation of spring brakes?

1. Check for tire wear

2. Ensure air pressure falls below 60 psi

3. Verify the spring brakes engage at low air pressure

4. Ensure the vehicle is leveled

The correct answer is: Verify the spring brakes engage at low air pressure

To ensure the safe operation of spring brakes, it is essential for a driver to verify that the spring brakes engage at low air pressure. Spring brakes are a crucial safety feature in vehicles equipped with air brake systems, designed to automatically apply brakes when the air pressure drops to a certain threshold, usually around 60 psi or lower. This automatic engagement helps to prevent the vehicle from rolling away when the air pressure fails or is insufficient to keep the service brakes operational. This focus on the engagement of spring brakes is vital because it ensures that in the event of an air leak or failure, the vehicle remains safely stopped. This is particularly important in large or heavy vehicles where uncontrolled movement could lead to serious accidents. The other options, while relevant to vehicle maintenance and safety, do not directly pertain to the specific function and operation of spring brakes. Checking tire wear or ensuring the vehicle is leveled does not influence how the spring brakes function. Additionally, simply ensuring that air pressure falls below 60 psi does not guarantee safe operation; it omits the critical step of confirming that the brakes engage appropriately at such pressures. Thus, the emphasis on verifying the engagement of the spring brakes under low air pressure directly relates to the core function of maintaining safety in air brake systems.