CDL air brakes practice testAir brakes, finally clear.
The gauge, the governor and the air brake check as live animations, then practice for your state’s air brakes test.
The lesson plan
25 lessons in 5 chapters · about 5 minutes each
1How air brakes work5
5.0 Air Brakes; 5.1 The Parts of an Air Brake System (5.1.1–5.1.10)
- Reading the air brake pressure gauge Lesson 1 · free
- Three brake systems in one
- Compressor, governor and safety valve
- Keeping the air clean and dry
- Foundation brakes and slack adjusters
2Warnings, valves and spring brakes5
5.1 The Parts of an Air Brake System (5.1.11–5.1.15); 5.2 Dual Air Brake
- The low-air warning
- Stop light switch and limiting valve
- Spring brakes: the fail-safe
- Parking brake controls
- Primary and secondary air systems
3Inspecting air brakes6
5.3 Inspecting Air Brake Systems
- Air brakes in the seven-step inspection
- Checking slack adjusters and drums
- Governor cut-in and cut-out test
- Static and applied leakage tests
- Low-air warning and spring brakes test
- Build-up rate and brake tests
4Using air brakes5
5.1.16 Antilock Braking Systems (ABS); 5.4 Using Air Brakes
- Normal stops and ABS
- Controlled and stab braking
- Brake lag and stopping distance
- Brake fade on long downgrades
- Low air pressure and parking
5Trailers and your test4
6.2 Combination Vehicle Air Brakes; 49 CFR 383.95 air brake restriction
- Trailer air lines and glad hands
- Tractor protection and trailer supply valves
- The air brake restriction
- Test day
Built on CDL Manual (AAMVA 2025 CDL Testing System), Section 5 Air Brakes and 6.2 Combination Vehicle Air Brakes; 49 CFR 383.111(b) · March 2025
Read lesson 1: Reading the air pressure gauge
You push the brake pedal to apply the brakes. Pushing harder applies more air pressure.
Air enters the brake chambers and pushes rods outward. Those rods move the parts that turn the brake camshaft.
Pressing and releasing the pedal unnecessarily can use air faster than the compressor replaces it. If pressure gets too low, your brakes won't work.
This gauge shows your supply pressure. A dual system shows each half, primary and secondary: two gauges, or one gauge with two needles. Watch both.
Start the engine and the compressor builds pressure. At about one twenty five the governor cuts out.
Use the brakes and pressure drops. Around one hundred psi the governor cuts back in and refills the tanks.
The low air warning must come on before pressure drops below…
- 100 psi
- 60 psi
- 20 psi
Answer: 60 psi. A warning, usually a red light, must come on before 60 psi. Stop and park safely as soon as you can. (Texas manual: 55.)
Keep losing air and the spring brakes come on between twenty and forty five psi, ready or not.
Next lesson: Three brake systems in one
The full class, $19 at launch.
Paid once, when it opens. Lesson 1 is free now.
- Animated systems
- Your state’s manual numbers
- Practice tests that explain
Not affiliated with FMCSA or any state DMV. Check your state’s CDL manual.
Questions
Is air brakes an endorsement?
No, it’s a separate knowledge test. Skip it, or take your skills test without air brakes, and your CDL carries an air brake restriction.
What is the air brake check?
The last step of the seven-step inspection in the CDL manual: the low-air warning, spring brakes, governor cut-in and cut-out, leakage rate, and parking and service brakes.
Do the numbers differ by state?
Some do, so our practice uses your state manual’s numbers. Check yours before test day.
When does it open, and what will it cost?
Lesson 1 is free now. The full class opens at $19, paid once.