Free 20-question practice test covering air brake systems, pressure limits, spring brakes, and pre-trip inspection. The air brakes section is one of the most commonly failed — use this test to make sure you're ready.
All Alabama CDL Practice Tests by Chapter
The low air pressure warning light and buzzer must activate before air pressure drops below 60 psi. Normal operating range is 100–125 psi.
Yes. If you plan to drive a vehicle with air brakes, you must pass the air brakes knowledge test as part of your CDL permit exam at ALEA. Failing to take this test results in an air brake restriction on your license.
Spring brakes automatically apply when air pressure drops into the 20–45 psi range. They are held open by air pressure — loss of air causes automatic application.
With brakes applied, air pressure should not drop more than 3 psi per minute in a single vehicle, or 4 psi per minute in a combination vehicle.
Brake fade is caused by heat buildup from extended or repeated brake application. As drum temperature rises, the friction coefficient of the lining drops — reducing braking effectiveness. Use engine braking and short, firm applications rather than riding the brakes continuously.