Michigan CDL - Air Brakes Practice Exam

Air brakes operate on the principle of utilizing compressed air, which is stored in tanks and then released to create pressure that activates the braking system. When the driver applies the brakes, air is allowed to flow from the storage tanks through the brake lines to various components, ultimately pushing the brake shoes against the drum or applying the brake pads against the rotor, thereby slowing down the vehicle. This system is particularly effective for large vehicles, as it can easily handle the significant weight and momentum of trucks and buses.

In contrast, hydraulic brakes rely on fluid pressure. When the brake pedal is pressed, hydraulic fluid is forced through brake lines to the brake components, which then results in the application of the brakes. This system is common in passenger vehicles where the weights and dynamics are different compared to heavy-duty vehicles.

Understanding that the distinction is fundamentally tied to the medium used—compressed air for air brakes and hydraulic fluid for hydraulic brakes—clarifies why the correct choice focuses on this operational difference. Each system has its unique advantages tailored to specific vehicle types and usage scenarios.