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CDL Air Brakes practice test
You need this knowledge to drive any truck with air brakes. Practise the parts, the gauges and the inspection tests that most applicants find confusing.
What this test covers
Compressor, governor, air tanks and drain valves, safety relief valve, alcohol evaporator, service, parking and emergency brakes, spring brakes, the low-air warning, dual systems, slack adjusters, gladhands, leakage tests and brake use on grades.
Study tips
- Learn the key numbers: 100 and 125 psi, 60 psi, 20 to 45 psi and 150 psi.
- Learn the order of the pre-trip air brake checks.
- Understand why spring brakes apply when air is lost, not just that they do.
More free CDL practice
Common questions
Do I need an air brakes test for my CDL?
If you want to drive vehicles with air brakes you must pass the air brakes knowledge test. If you do not pass it, or take your skills test in a vehicle without air brakes, your licence carries an air brake restriction.
What pressure numbers should I know?
Typical values are a governor cut-in around 100 psi and cut-out around 125 psi, a low-air warning before 60 psi, spring brakes applying between about 20 and 45 psi, and a safety relief valve around 150 psi. Your vehicle and your state's manual may differ slightly.
What are the leakage test limits?
With brakes released and the engine off, a single vehicle should lose no more than 2 psi in a minute and a combination vehicle no more than 3 psi. With the service brake fully applied, the limits are about 3 psi for a single vehicle and 4 psi for a combination.
Are these the real test questions?
No. These are original practice questions. Your state test uses its own wording, so always study your state CDL manual.