CDL air brakes test questions: key concepts to know

Concepts that come up often

• Governor: the compressor stops pumping at the cut-out pressure (the manual's example is about 125 psi) and starts again at cut-in
• Low pressure warning: must come on before pressure drops below 60 psi
• Spring brakes: come on automatically when pressure drops far enough (the manual's example range is 20 to 45 psi)
• Draining tanks: drain water and oil from air tanks daily
• Dual air systems: two separate systems each hold pressure
• Brake lag: air brakes take a moment to apply after you press the pedal

Air leakage check

The test often asks about the static and applied leakage check, where you hold the brake and watch the pressure drop. Allowed leakage rates differ for single and combination vehicles, so learn the exact numbers from your state manual's table.

How to study

• Put every number question in one table and memorize it.
• Read the inspection steps out loud in order.
• Retry each miss until you get it right twice in a row.

Doing it with Haulprep

Practice the Air Brakes topic in Haulprep 10 questions at a time with explanations. Misses go to your mistakes notebook, and when readiness passes 80% take the 25-question mock test.

Note

This guide is general study information. Question counts, fees and test procedures vary by state and can change, so always check your state's current CDL manual and DMV. Haulprep is not affiliated with FMCSA or any state DMV. Official source: https://www.fmcsa.dot.gov/cdl