CertReady
Commercial DrivingFederal certification87 free questions

CDL: Air Brakes

Required if you will drive a vehicle with air brakes. Dual air systems, lag, slack adjusters, spring brakes, ABS and leak tests.

Start practicingTake a mock exam

16

practice questions

13

free questions

20%

of the real exam

Practice Air Brakes questionsRead the study guide

What this section covers

If the truck you will drive has air brakes, you must pass the Air Brakes knowledge test — typically 25 questions, 80%. Skip it and your CDL is restricted: no air-brake vehicles.

Numbers and parts to lock in:

  • Dual air systems (primary and secondary)
  • Low-air warning at or above 60 psi
  • Spring (parking / emergency) brakes apply as air is lost
  • Extra brake lag versus hydraulic brakes
  • Slack-adjuster travel, tank drains, ABS (do not pump)
  • Applied leakage: 2 psi / minute single vehicle, 3 psi / minute combination

This section is independent of class. A Class B dump truck with air brakes still needs it. Practice: Air Brakes.

Other CDL sections