CDL Air Brakes Practice Test 2026: Quiz di prova 3

1. Domanda 1 di 30

   Which of these is a problem with brake linings?

   • ALinings that are clean and dry
   • BLinings soaked with oil or grease
   • CLinings that are firmly attached
   • DLinings of normal, even thickness
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   Risposta: B. Linings soaked with oil or grease

   Linings must not be loose, soaked with oil or grease, or dangerously thin.

2. Domanda 2 di 30

   How do you test the low pressure warning signal?

   • ADrain the tanks while driving and see when the light comes on
   • BEngine off, key on, pump the brake pedal; it must come on before 60 psi
   • CRun the engine at high rpm until the warning light comes on
   • DPull out the trailer air supply knob and watch the gauge
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   Risposta: B. Engine off, key on, pump the brake pedal; it must come on before 60 psi

   Turn the engine off, turn the key to power, and step on and off the brake to lower pressure. The warning must come on before 60 psi.

3. Domanda 3 di 30

   During the spring brake test, you keep pumping the brake pedal to lower air pressure. What should happen?

   • AThe parking brake knob should pop out
   • BThe safety valve should open and release air
   • CThe governor should cut out the compressor
   • DNothing should happen until 0 psi
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   Risposta: A. The parking brake knob should pop out

   As pressure falls to the maker's level, the tractor protection valve and parking brake valve should close and pop out.

4. Domanda 4 di 30

   How do you check the governor's cut-in and cut-out pressures?

   • AAt fast idle, pumping should stop near 125 psi and restart near 100 psi
   • BOpen the safety valve by hand and listen for the compressor
   • CDrive at 55 mph and read the gauge while braking hard
   • DShut the engine off and watch the gauge for one full hour
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   Risposta: A. At fast idle, pumping should stop near 125 psi and restart near 100 psi

   With the engine at fast idle, the compressor should cut out near 125 psi. Lower the pressure with the brake pedal; it should cut in near 100 psi.

5. Domanda 5 di 30

   For the air leakage test, how should you set up the vehicle?

   • ATanks drained to 60 psi, engine running
   • BFully charged, engine off, parking brake released
   • CParking brake applied and engine running
   • DEngine running at high rpm, brakes applied
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   Risposta: B. Fully charged, engine off, parking brake released

   With a fully charged system (typically 125 psi), turn off the engine, release the parking brake and time the pressure drop.

6. Domanda 6 di 30

   A single vehicle's brakes are released and the engine is off. What is the most air pressure it should lose in one minute?

   • ALess than 2 psi
   • BNo loss at all
   • CLess than 5 psi
   • DLess than 10 psi
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   Risposta: A. Less than 2 psi

   With brakes released, a single vehicle should lose less than 2 psi per minute.

7. Domanda 7 di 30

   A combination vehicle's brakes are released and the engine is off. What is the most air pressure it should lose in one minute?

   • ALess than 3 psi
   • BLess than 8 psi
   • CLess than 15 psi
   • DLess than 1 psi
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   Risposta: A. Less than 3 psi

   With brakes released, a combination vehicle should lose less than 3 psi per minute.

8. Domanda 8 di 30

   With the brakes applied at 90 psi or more, what is the most air a single vehicle should lose per minute after the first drop?

   • A10 psi
   • B1 psi
   • C6 psi
   • D3 psi
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   Risposta: D. 3 psi

   With the brakes applied, the leakage should be no more than 3 psi per minute for a single vehicle.

9. Domanda 9 di 30

   With the brakes applied at 90 psi or more, what is the most air a combination vehicle should lose per minute after the first drop?

   • A12 psi
   • B2 psi
   • C4 psi
   • D8 psi
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   Risposta: C. 4 psi

   With the brakes applied, a combination vehicle should lose no more than 4 psi per minute.

10. Domanda 10 di 30

    Your vehicle loses air faster than the allowed leakage rate. What should you do?

    • ADrain the tanks and drive
    • BHave the leaks fixed before driving
    • CDrive slowly to the next stop
    • DRaise the governor setting
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    Risposta: B. Have the leaks fixed before driving

    Too much leakage means the system needs repair before the vehicle is driven.

11. Domanda 11 di 30

    Air pressure builds up too slowly during your inspection. What should you do?

    • ADo not drive until it is fixed
    • BDrive and let it build on the road
    • CTurn off the low air warning
    • DPump the brakes to build pressure faster
    Mostra la risposta

    Risposta: A. Do not drive until it is fixed

    If pressure builds too slowly, the system could fail. Have it fixed before driving.

12. Domanda 12 di 30

    With a belt-driven air compressor, what should you check in the engine compartment?

    • AThat the belt is loose enough to slip
    • BThat the belt is wet with oil
    • CThat the belt is in good shape and tight
    • DThat the belt is removed for summer
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    Risposta: C. That the belt is in good shape and tight

    If the compressor is belt-driven, make sure the belt is in good condition and properly tight.

13. Domanda 13 di 30

    When making a normal stop with a manual transmission, when should you push in the clutch?

    • AWhen engine rpm is near idle
    • BBefore you start to brake
    • CNever during a normal stop
    • DAs soon as you start braking
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    Risposta: A. When engine rpm is near idle

    Wait until the engine is near idle before pushing in the clutch, then choose a starting gear once stopped.

14. Domanda 14 di 30

    Using the stab braking method, how long can it take for locked wheels to start rolling again after you release the brakes?

    • AThey start rolling instantly
    • BAbout ten seconds
    • CAbout five seconds
    • DUp to one second
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    Risposta: D. Up to one second

    It can take up to one second for the wheels to roll after you release. If you reapply too soon, the vehicle won't straighten out.

15. Domanda 15 di 30

    Why does a vehicle with air brakes take longer to stop than one with hydraulic brakes?

    • AAir brakes are weaker than hydraulic brakes
    • BAir brakes only work on the rear wheels
    • CAir takes time to flow to the brakes (brake lag)
    • DThe governor holds back air when you brake
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    Risposta: C. Air takes time to flow to the brakes (brake lag)

    Air brakes take about half a second or more to work after you press the pedal. This is called brake lag.

16. Domanda 16 di 30

    At 55 mph on dry pavement, about how much distance does air brake lag add?

    • AAbout 100 feet
    • BAbout 3 feet
    • CAbout 300 feet
    • DAbout 32 feet
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    Risposta: D. About 32 feet

    At 55 mph, the air brake lag adds about 32 feet to stopping distance.

17. Domanda 17 di 30

    About how far does it take a vehicle with air brakes to stop from 55 mph on dry pavement?

    • AAbout 250 feet
    • BAbout 1,000 feet
    • COver 450 feet
    • DAbout 150 feet
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    Risposta: C. Over 450 feet

    Total stopping distance at 55 mph with air brakes is over 450 feet.

18. Domanda 18 di 30

    Which four parts make up total stopping distance for a vehicle with air brakes?

    • APerception, reaction, coasting and braking distance
    • BPerception, reaction, brake lag and effective braking distance
    • CReaction, shifting, braking and skidding distance
    • DFollowing, perception, braking and parking distance
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    Risposta: B. Perception, reaction, brake lag and effective braking distance

    Air brakes add brake lag to the usual perception, reaction and braking distances.

19. Domanda 19 di 30

    What causes brake fade?

    • AToo much air pressure in the brake lines
    • BWater mixing with the fuel in cold weather
    • CCold air building up inside the tanks
    • DToo much heat from overusing the brakes
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    Risposta: D. Too much heat from overusing the brakes

    Excess heat reduces friction in the linings and makes the drums expand, so the brakes stop working well.

20. Domanda 20 di 30

    Some brakes on your vehicle are out of adjustment. How does this lead to brake fade?

    • AThe ABS stops working
    • BThe out-of-adjustment brakes get too cold
    • CThe other brakes do more work, overheat and fade
    • DThe air pressure rises too high
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    Risposta: C. The other brakes do more work, overheat and fade

    Brakes out of adjustment do less work, so the others overheat. Check adjustment often, because hot brakes can go out of adjustment fast.

21. Domanda 21 di 30

    You are going down a long grade in the proper low gear. When should you release the brakes?

    • AWhen your speed is about 5 mph below your safe speed
    • BOnly at the bottom of the grade
    • CWhen you reach 10 mph over your safe speed
    • DWhen you are 20 mph below your safe speed
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    Risposta: A. When your speed is about 5 mph below your safe speed

    Brake just enough to feel a definite slowdown, and release when you are about 5 mph below your safe speed.

22. Domanda 22 di 30

    On a downgrade, about how long should each brake application last?

    • AAbout 30 seconds
    • BLess than half a second
    • CAbout 1 minute
    • DAbout 3 seconds
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    Risposta: D. About 3 seconds

    Each application, from braking to release, should last about three seconds.

23. Domanda 23 di 30

    Your spring brakes come on because of low air pressure. Why might a heavy load take longer to stop?

    • ASpring brakes are stronger than service brakes
    • BSpring brakes only work on the steering axle
    • CSpring brakes do not work on all axles
    • DThe ABS turns off the spring brakes
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    Risposta: C. Spring brakes do not work on all axles

    With a heavy load, stopping on spring brakes takes longer because they are not on every axle.

24. Domanda 24 di 30

    When should you NOT use the parking brakes?

    • AWhenever you park on a hill or a slope
    • BWhen brakes are very hot, or very wet in freezing weather
    • CWhenever the engine is turned off
    • DAt the end of the working day
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    Risposta: B. When brakes are very hot, or very wet in freezing weather

    Very hot brakes can be damaged by the parking brakes, and very wet brakes can freeze in place in cold weather.

25. Domanda 25 di 30

    Your brakes are very hot after a long downgrade and you need to park on a level surface. What should you do?

    • AChock the wheels and let the brakes cool first
    • BSpray the brakes with water to cool them quickly
    • CSet the parking brake right away to hold the truck
    • DLeave the engine running in gear to hold the truck
    Mostra la risposta

    Risposta: A. Chock the wheels and let the brakes cool first

    Do not set the parking brakes on very hot brakes. Chock the wheels and let them cool.

26. Domanda 26 di 30

    Your brakes are wet and it is freezing outside. How can you keep them from freezing?

    • ADrain the air tanks before you park the truck
    • BBrake lightly in a low gear to heat and dry them
    • CPump the brake pedal many times while parked
    • DSet the parking brake firmly as soon as you stop
    Mostra la risposta

    Risposta: B. Brake lightly in a low gear to heat and dry them

    Use the brakes lightly in a low gear to warm and dry them before parking.

27. Domanda 27 di 30

    When may you leave a vehicle unattended?

    • AAny time you will be gone less than 10 minutes
    • BOnly with parking brakes set or wheels chocked
    • CAfter turning off the engine, nothing more
    • DAfter shifting into neutral and locking the cab
    Mostra la risposta

    Risposta: B. Only with parking brakes set or wheels chocked

    Never leave a vehicle unattended without applying the parking brakes or chocking the wheels.

28. Domanda 28 di 30

    Your vehicle has ABS on the tractor only. How should you brake?

    • ABrake as hard as possible every time you stop
    • BBrake normally and ease off if the trailer starts to swing
    • CUse only the trailer hand brake to stop the rig
    • DPump the brake pedal very fast in every stop
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    Risposta: B. Brake normally and ease off if the trailer starts to swing

    Even partial ABS helps. Brake the same way and ease off if the trailer swings or the tractor starts to jackknife.

29. Domanda 29 di 30

    When may you fully apply the brakes in an emergency stop?

    • AOnly on dry roads without ABS
    • BWhen all axles have working ABS
    • CNever, with air brakes
    • DAlways, on any vehicle
    Mostra la risposta

    Risposta: B. When all axles have working ABS

    With working ABS on every axle, you can fully apply the brakes in an emergency stop.

30. Domanda 30 di 30

    What should you check on the air hoses connected to the brake chambers?

    • AThat they are filled with oil
    • BThat they are disconnected
    • CThat they are not cut or worn
    • DThat they are painted red
    Mostra la risposta

    Risposta: C. That they are not cut or worn

    Check that air hoses to the brake chambers are not cut or worn from rubbing.

Tastiera: 1–4 per rispondere, Invio per la domanda successiva.

Il test reale: Varies by state; usually 25 questions, with 20 correct needed (80%)