Free CDL Air Brakes Practice Test 2025

The Air Brakes test has two parts: a written knowledge test about air brake systems, and a skills test where you demonstrate air brake operation in an actual vehicle. Passing both removes the "L" (air brake) restriction from your CDL.

Your CDL will have an "L" restriction, meaning you can only drive commercial vehicles WITHOUT air brakes. Since most trucks and buses use air brakes, this severely limits your job options.

Air brakes use compressed air instead of hydraulic fluid to stop the vehicle. The air compressor pumps air into tanks, and when you press the brake pedal, air pressure pushes against the brake chambers to apply the brakes.

Brake lag is the time it takes for air to travel through the lines and apply the brakes after you press the pedal. At 55 mph, brake lag adds about 32 feet to your stopping distance.

Spring brakes are emergency/parking brakes that use powerful springs. When air pressure drops (like from a leak), the springs push out and apply the brakes automatically. This is a safety feature.

25 questions, multiple choice. You need 20 right to pass (80%). The test covers air brake components, inspection, and emergency procedures.

The test covers: air brake system parts, dual air brake systems, inspecting air brakes, using air brakes, brake adjustment, low pressure warnings, and emergency stopping.

Drain air tanks at the end of each day of driving. Water and oil accumulate in the tanks and can freeze in cold weather, causing brake failure.

The air compressor should maintain tank pressure between about 100-125 psi. The governor cuts in around 100 psi and cuts out around 125 psi.

Yes! You'll need to pass the written Air Brakes knowledge test AND take a skills test in a vehicle equipped with air brakes. During the skills test, you'll demonstrate air brake checks including pumping the brake pedal until pressure drops and the emergency knobs pop out.