CDL Air Brakes Practice Test 2026：第2套练习测试

1. 第1题，共25题

   What is a wig wag?

   • AA type of flashing brake light on the trailer
   • BA device that wags the trailer to warn drivers
   • CA switch that releases the spring brakes
   • DA metal arm that drops into view when air is low
   显示答案

   答案: D. A metal arm that drops into view when air is low

   A wig wag is a low pressure warning device: a mechanical arm that drops into your view when pressure falls below 60 psi.

2. 第2题，共25题

   What does the stop light switch do in an air brake system?

   • ATurns on the brake lights when you brake
   • BApplies the spring brakes when air is low
   • CStops the compressor at cut-out pressure
   • DTurns off the engine when pressure is low
   显示答案

   答案: A. Turns on the brake lights when you brake

   An air-pressure switch turns on the brake lights when the brakes are applied.

3. 第3题，共25题

   Some older vehicles have a front brake limiting valve with a "normal" and "slippery" setting. Where should you keep it?

   • AIt does not matter
   • BIn the "normal" position
   • CIn the "slippery" position at all times
   • DIn "slippery" on dry roads only
   显示答案

   答案: B. In the "normal" position

   The slippery setting cuts air to the front brakes by half, which reduces stopping power. Keep it in normal.

4. 第4题，共25题

   How are spring brakes held off during normal driving?

   • ABy air pressure
   • BBy the parking brake cable
   • CBy the governor
   • DBy hydraulic fluid
   显示答案

   答案: A. By air pressure

   Spring brakes are held back by air pressure. When air is lost, the springs put on the brakes.

5. 第5题，共25题

   When will the spring brakes on a tractor or straight truck come fully on?

   • AWhen air pressure falls below 100 psi
   • BWhen air pressure falls to about 20 to 45 psi
   • CWhen air pressure rises above 125 psi
   • DOnly when the driver pulls the yellow knob
   显示答案

   答案: B. When air pressure falls to about 20 to 45 psi

   Spring brakes come fully on when air pressure drops to a range of 20 to 45 psi, typically 20 to 30 psi.

6. 第6题，共25题

   The low air pressure warning comes on while you are driving. What should you do?

   • APump the brakes to build pressure
   • BSpeed up to charge the tanks faster
   • CStop and park safely as soon as possible
   • DKeep driving to the next terminal
   显示答案

   答案: C. Stop and park safely as soon as possible

   There may be an air leak. Controlled braking is only possible while enough air remains, so stop safely right away.

7. 第7题，共25题

   Why should you not push the brake pedal down when the spring brakes are on?

   • AIt turns off the ABS
   • BThe combined force can damage the brakes
   • CIt will raise the air pressure
   • DIt will release the spring brakes
   显示答案

   答案: B. The combined force can damage the brakes

   Pushing the pedal while the spring brakes are on adds the two forces together and can damage the brakes.

8. 第8题，共25题

   What does the parking brake control look like on newer vehicles?

   • AA green lever beside the seat
   • BA red, eight-sided knob
   • CA blue, round push-pull knob
   • DA yellow, diamond-shaped knob
   显示答案

   答案: D. A yellow, diamond-shaped knob

   Newer vehicles use a yellow, diamond-shaped knob. The red eight-sided knob is the trailer air supply.

9. 第9题，共25题

   How do you use the yellow parking brake knob?

   • APush it in to apply; pull it out to release
   • BPull it out to apply; push it in to release
   • CHold it down for as long as you are parked
   • DTurn it to the left to apply the brakes
   显示答案

   答案: B. Pull it out to apply; push it in to release

   Pull the knob out to put the parking brakes on, and push it in to release them.

10. 第10题，共25题

    What does a modulating control valve let you do?

    • ADrain all the air tanks from inside the cab
    • BApply the spring brakes a little at a time
    • CChange the governor's cut-in and cut-out settings
    • DTurn the antilock brake system on and off
    显示答案

    答案: B. Apply the spring brakes a little at a time

    A modulating control valve is a lever on the dash that lets you apply the spring brakes a little at a time.

11. 第11题，共25题

    Some vehicles have dual parking control valves with a separate small air tank. What is it for?

    • AFilling the tires with air when one goes low
    • BGiving the air horn its own supply of air
    • CReleasing the spring brakes briefly in an emergency
    • DMaking the parking brakes hold more strongly
    显示答案

    答案: C. Releasing the spring brakes briefly in an emergency

    The separate tank holds only enough air to release the spring brakes a few times, so plan your moves carefully.

12. 第12题，共25题

    Truck tractors with air brakes built on or after what date must have antilock brakes (ABS)?

    • AJuly 1, 2010
    • BJanuary 1, 1990
    • CMarch 1, 2005
    • DMarch 1, 1997
    显示答案

    答案: D. March 1, 1997

    Air-braked truck tractors built on or after March 1, 1997 must have ABS. Other air-braked vehicles built on or after March 1, 1998 must too.

13. 第13题，共25题

    Which air-braked vehicles built on or after March 1, 1998 must have ABS?

    • ATrucks, buses, trailers and converter dollies
    • BOnly school buses and transit buses
    • COnly tank vehicles hauling hazmat
    • DOnly truck tractors pulling trailers
    显示答案

    答案: A. Trucks, buses, trailers and converter dollies

    Besides tractors (from March 1, 1997), other air brake vehicles built on or after March 1, 1998 must have antilock brakes.

14. 第14题，共25题

    What does it mean if your ABS lamp comes on for a moment when you start the vehicle and then goes out?

    • AThe ABS has failed
    • BIt is a normal bulb check
    • CThe parking brake is off
    • DThe air tanks are empty
    显示答案

    答案: B. It is a normal bulb check

    Newer systems light the ABS lamp briefly at start-up as a bulb check, then turn it off.

15. 第15题，共25题

    Does ABS shorten your stopping distance?

    • AYes, it always cuts stopping distance in half
    • BYes, but only on dry roads
    • CNo, it makes stopping distance much longer
    • DNot necessarily; it helps you keep steering control
    显示答案

    答案: D. Not necessarily; it helps you keep steering control

    ABS does not change normal braking ability or always shorten stopping distance. It prevents lockup so you can steer.

16. 第16题，共25题

    In a dual air brake system, which brakes does the primary system usually run?

    • AThe front brakes
    • BThe rear brakes
    • COnly the parking brakes
    • DOnly the trailer brakes
    显示答案

    答案: B. The rear brakes

    The primary system usually works the rear axle brakes. The secondary works the front brakes and maybe one rear axle.

17. 第17题，共25题

    Before driving a vehicle with a dual air system, how much pressure should the compressor build in both systems?

    • AAt least 150 psi
    • BAt least 40 psi
    • CAt least 100 psi
    • DAt least 60 psi
    显示答案

    答案: C. At least 100 psi

    Let the compressor build up at least 100 psi in both the primary and secondary systems before driving.

18. 第18题，共25题

    In a dual air system, how quickly should pressure build from 85 to 100 psi at operating rpm?

    • AWithin about 3 minutes
    • BWithin about 45 seconds
    • CWithin about 5 seconds
    • DWithin about 10 minutes
    显示答案

    答案: B. Within about 45 seconds

    In dual systems, pressure should go from 85 to 100 psi within 45 seconds. Larger tanks may take longer; check the specifications.

19. 第19题，共25题

    What is the main job of the slack adjuster?

    • AIt tells the compressor when to pump
    • BIt drains water from the air tanks
    • CIt turns on the brake lights when braking
    • DIt links the push rod to the brake camshaft
    显示答案

    答案: D. It links the push rod to the brake camshaft

    The push rod turns the slack adjuster, which turns the camshaft and S-cam to apply the brakes.

20. 第20题，共25题

    You pull hard on a slack adjuster with the brakes released. How far can it move before it probably needs adjusting?

    • AIt should never move at all, even slightly
    • BAbout one inch where the push rod attaches
    • CAbout one-eighth inch at the end of the arm
    • DAbout six inches at the end of the arm
    显示答案

    答案: B. About one inch where the push rod attaches

    If a slack adjuster moves more than about one inch where the push rod attaches, it probably needs adjustment.

21. 第21题，共25题

    What must you do before checking slack adjusters?

    • ASet the parking brakes and run the engine
    • BRaise the vehicle on a jack so wheels turn
    • CDrain the air tanks completely first
    • DChock the wheels and release the parking brakes
    显示答案

    答案: D. Chock the wheels and release the parking brakes

    To check slack adjusters you must release the parking brakes, so chock the wheels first on level ground.

22. 第22题，共25题

    What is the most common problem found in roadside inspections of air brakes?

    • AMissing reflective triangles
    • BBrakes out of adjustment
    • CEmpty alcohol evaporators
    • DBroken brake lights
    显示答案

    答案: B. Brakes out of adjustment

    Out-of-adjustment brakes are the number one problem inspectors find.

23. 第23题，共25题

    Your vehicle has automatic slack adjusters. Do they still need to be checked?

    • ANo, they adjust themselves
    • BOnly once a year at service
    • CYes, during every inspection
    • DOnly after a crash or a fault
    显示答案

    答案: C. Yes, during every inspection

    Vehicles built since 1994 have automatic slack adjusters, but they must still be checked.

24. 第24题，共25题

    An automatic slack adjuster is out of adjustment. What does this usually mean?

    • AThere is probably a mechanical problem that needs repair
    • BThe tanks need draining
    • CThe governor is set too high
    • DIt just needs a quick manual adjustment and no repair
    显示答案

    答案: A. There is probably a mechanical problem that needs repair

    Manual adjustment of an automatic adjuster is only a temporary emergency fix. Have the vehicle repaired as soon as possible.

25. 第25题，共25题

    How long can a crack in a brake drum be?

    • AAny length, as long as it is not leaking
    • BUp to the full width of the friction area
    • CUp to half the width of the friction area
    • DUp to 6 inches, measured along the drum
    显示答案

    答案: C. Up to half the width of the friction area

    Drum cracks must not be longer than one-half the width of the friction area.

键盘：按1–4作答，按 Enter 进入下一题。

真实考试：Varies by state; usually 25 questions, with 20 correct needed (80%)