CDL (Commercial Driver's License) Practice Test (Air Brakes #2)


Welcome future truck drivers! The following is the CDL Air Brakes Practice Test #2. If you're going to drive a commercial vehicle with air brakes, you'll need an Air Brakes Endorsement on your CDL (Commercial Driver's License). Simply click in your answer (A,B,C, or D) to each CDL practice test question. When you're done, check your score and the results. You can reset the test and retake it as many times as you want.

CDL Air Brakes Practice Test #2

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1. Modern air brake systems combines three different systems. The are the service brakes, the parking brakes and the:

A S-cam brakes.
B Drum brakes.
C Foot brakes.
D Emergency brakes.

2. Oil and water usually collect in compressed air tanks. If you do not have an automatic tank drain, when should you drain the air tanks?

A After every working day.
B After every four hours of service.
C Once a week.
D Every other week.

3. Why drain water from the compressed air tanks?

A To keep from fouling the air compressor oil.
B Water can freeze in cold weather and cause brake failure.
C The low boiling point of water reduces braking power.
D Water over cools the compressor.

4. Air brake equipped vehicles must have:

A A supply pressure gauge.
B An air use gauge.
C At least two brake heaters.
D A backup hydraulic system.

5. What can legally hold a parking or emergency brake in position for a truck, truck tractor or bus?

A Fluid pressure
B Air pressure
C Spring pressure
D Any of the above

6. Air loss in a straight truck or bus should not be more than ____ with the engine off and the brakes on.

A 1 psi in 30 seconds
B 1 psi in one minute
C 2 psi in 45 seconds
D 3 psi in one minute

7. To make an emergency stop with air brakes, using the stab braking method, you should:

A Pump the brake pedal rapidly and lightly.
B Brake hard until the wheels lock, and then get off the brakes for as much time as the wheels were locked
C Brake as hard as you can, get off the brakes when the wheels lock, get back on the brakes when the wheels start rolling again.
D Press hard on the brake pedal and apply full hand valve until you stop.

8. You should know that your brakes are fading when:

A Pressure on the brake pedal is released and speed increases.
B You have to push harder on the brake pedal to control your speed on a downgrade.
C The brake feels spongy when pressure is applied
D Less pressure is needed on the brake pedal for each stop

9. To check the free play of manual slack adjusters on s-cam brakes you should:

A Park on level ground, chock the wheels, and release the parking brakes.
B Stop on level ground and apply the parking brakes.
C Park on level ground and drain off air pressure before adjusting.
D Park on a slight grade, release the parking brake, apply the service brakes, and check for vehicle movement.

10. If the air compressor should develop a leak, what keeps the air in the tanks?

A The tractor protection valve
B The emergency relay valve
C The one way check valve
D The air compressor

11. When driving down a long steep hill you should:

A Use stab braking.
B Begin braking when you are 10 M.P.H. above your safe speed.
C Release the brake when you are 5 M.P.H. below your safe speed.
D Use the trailer brakes.

12. The brake system that applies and releases the brakes when the driver uses the brake pedal is the:

A Service brake system.
B Emergency brake system.
C Parking brake system.
D None of the above.

13. The most common type of foundation brakes found on heavy vehicles is the:

A Disc brakes
B Wedge drum
C S-cam drum
D None of the above

14. Vehicles with air brakes must have:

A At least two air tanks.
B An air pressure gauge to show the pressure available for braking.
C An air pressure gauge, to show air used by the brake chambers for braking.
D None of the above.

15. The driver must be able to see a warning that is given before air pressure in the service air tanks falls below:

A 80 psi
B 40 psi
C 20 psi
D 60 psi

16. Which of the following makes the total stopping distance for air brakes longer than that for hydraulic brakes.

A Brake lag distance.
B Action distance.
C Perception distance.
D Effective braking distance.

17. Of the choices below, the first thing to do when a low air pressure warning comes on is:

A Open the air supply control valve.
B Adjust the brake pedal for more travel.
C Stop and safely park as soon as possible.
D Up-shift.

18. The braking power of the spring brakes:

A Can only be tested by highly trained brake service people.
B Depends on the adjustment of the service brakes.
C Increases when the service brakes are hot.
D Is not affected by the condition of the service brakes.

19. The air compressor governor controls:

A When air is pumped into the air tanks.
B Air pressure applied to the brakes.
C The speed of the air compressor.
D When the brake chambers release pressure.

20. The application pressure gauge shows the driver how much pressure:

A Has been used on the trip.
B Is in the air tanks.
C None of these.
D Is being applied to the brakes.

21. If your vehicle has an alcohol evaporator, every day during cold weather you should:

A Clean the air filter with alcohol.
B Check and fill the alcohol level.
C Change the alcohol from a new bottle.
D Check the oil for alcohol content.

22. During normal driving, spring brakes are usually held back by:

A Spring pressure
B Bolts or clamps
C Centrifugal force
D Air pressure

23. Air braking takes more time than hydraulic braking because air brakes:

A Need to have airflow through the lines to work.
B Use different brake drums.
C Require heavier return springs.
D All of the above.

24. In air brake vehicles, the parking brakes should be used:

A To hold your speed when going downhill.
B Whenever the vehicle is parked.
C As little as possible.
D Only during pre and post trip inspections.

25. The brake pedal in an air brake system:

A Is to be used as a footrest during normal driving.
B Controls the speed of the air compressor.
C Controls the air pressure applied to put on the brakes.
D Is connected to slack adjusters by a series of rods and linkages.

26. If your truck or bus has dual parking control valves it means that you can use pressure from a separate tank to:

A Balance the service brake system.
B Release the spring brakes to move a short distance.
C Stay parked without using up service air pressure.
D Apply more brake pressure if the main tank is getting low.

27. A straight truck or bus air brake system should not leak at a rate of more than ____ PSI per minute with the engine off and the brakes released.

A 4
B 3
C 2
D 1

28. If your vehicle has an alcohol evaporator, it is there to:

A Reduce the risk of ice in air brake valves in cold weather.
B Eliminate the need for daily tank draining.
C Rid the wet tank of alcohol that condenses and sits at the bottom.
D Boost tank pressure the same way that superchargers boost.

29. If you must make an emergency stop, you should brake so that you:

A Use the full power of the brakes and lock them.
B Can steer hard while braking hard.
C Stay in a straight line and can steer.
D Use the hand brake first.

30. Your truck or bus has a dual air brake system. If a low air pressure warning comes on for only one system, what should you do?

A Reduce your speed and drive to the nearest garage for repairs.
B Continue at normal speed and find a garage before the brakes lock.
C Reduce your speed and test the remaining system while under way.
D Stop. Safely park, and continue only after the system is fixed.

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