Montana Air Brakes Practice Questions

Air Brakes questions

1. 1. What is the primary function of an air brake system's governor?

   1. A. To control when air is pumped
   2. B. To limit vehicle speed
   3. C. To regulate engine idle

   Answer: A — To control when air is pumped

   The governor sets the cut-in and cut-out pressures for the air compressor.

2. 2. At what pressure must the low air pressure warning activate?

   1. A. Below 20 psi
   2. B. Below 100 psi
   3. C. Below 60 psi

   Answer: C — Below 60 psi

   The warning must come on before pressure drops below 60 psi in the air system.

3. 3. What should you do if the low air pressure warning comes on while driving?

   1. A. Pump the brake pedal to build pressure
   2. B. Stop safely as soon as possible and park
   3. C. Continue to the next service point

   Answer: B — Stop safely as soon as possible and park

   Continued loss of air will eventually apply the spring brakes without warning, so stop while you still have control.

4. 4. At roughly what pressure do the spring brakes apply automatically?

   1. A. Between 20 and 45 psi
   2. B. Between 60 and 80 psi
   3. C. Below 5 psi

   Answer: A — Between 20 and 45 psi

   Spring brakes come on somewhere between 20 and 45 psi as air pressure falls.

5. 5. What holds spring brakes in the released position?

   1. A. Hydraulic fluid
   2. B. An electric solenoid
   3. C. Air pressure

   Answer: C — Air pressure

   Air pressure compresses the spring; losing air lets the spring apply the brake.

6. 6. Why should you never use the parking brake while the brakes are very hot?

   1. A. It wears the spring brake chambers
   2. B. Hot brakes can be damaged by it
   3. C. It drains the air tanks

   Answer: B — Hot brakes can be damaged by it

   Applying a hot brake can damage the drums, and moisture can freeze the shoes to the drum in cold conditions.

7. 7. What is the maximum allowable air loss rate for a single vehicle with the engine off and brakes released?

   1. A. 2 psi per minute
   2. B. 5 psi per minute
   3. C. 10 psi per minute

   Answer: A — 2 psi per minute

   A single vehicle may lose no more than 2 psi per minute with the brakes released.

8. 8. What is the maximum allowable air loss for a combination vehicle with the brakes applied?

   1. A. 2 psi per minute
   2. B. 8 psi per minute
   3. C. 4 psi per minute

   Answer: C — 4 psi per minute

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

9. 9. Within what pressure range must the governor cut out?

   1. A. Around 200 psi
   2. B. Around 120 to 140 psi
   3. C. Around 60 to 80 psi

   Answer: B — Around 120 to 140 psi

   Typical cut-out pressure is between 120 and 140 psi, at which point the compressor stops pumping.

10. 10. Why must air tanks be drained regularly?

    1. A. To remove water and oil
    2. B. To reduce vehicle weight
    3. C. To reset the governor

    Answer: A — To remove water and oil

    Compressed air carries moisture and oil that collect in the tanks and can freeze the system in cold weather.

11. 11. What is brake lag in an air brake system?

    1. A. The time the driver takes to react
    2. B. The distance travelled after the brakes release
    3. C. The delay before air reaches the brake chambers

    Answer: C — The delay before air reaches the brake chambers

    Air takes time to travel through the lines, adding roughly half a second of distance at highway speed.

12. 12. How does brake lag change total stopping distance compared with a car?

    1. A. It reduces the braking distance
    2. B. It adds distance on top of reaction
    3. C. It has no effect

    Answer: B — It adds distance on top of reaction

    Air brake stopping distance is perception distance plus reaction distance plus brake lag distance plus effective braking distance.

13. 13. What does anti-lock braking do for a commercial vehicle?

    1. A. It helps you keep steering control
    2. B. It always shortens the stopping distance
    3. C. It replaces the need for the parking brake

    Answer: A — It helps you keep steering control

    ABS prevents wheel lock-up so the driver retains steering, but it does not make the vehicle stop in less distance.

14. 14. How should you brake in an emergency in a vehicle equipped with ABS?

    1. A. Pump the pedal rapidly
    2. B. Apply light pressure only
    3. C. Brake firmly and steer as needed

    Answer: C — Brake firmly and steer as needed

    The system modulates pressure itself; pumping the pedal defeats its operation.

15. 15. What does the trailer air supply valve control?

    1. A. The trailer's suspension height
    2. B. Air to the trailer's braking system
    3. C. The trailer's lights

    Answer: B — Air to the trailer's braking system

    Pushing the valve in supplies the trailer and releases its spring brakes; pulling it out applies them.

16. 16. Why should the trailer hand valve not be used for parking?

    1. A. Air may leak away and release the brakes
    2. B. It applies the tractor brakes too
    3. C. It is only for emergencies

    Answer: A — Air may leak away and release the brakes

    The hand valve is not a parking device; leaking air would let the trailer roll.

17. 17. What is the function of the air compressor in an air brake system?

    1. A. To cool the brake drums
    2. B. To apply the parking brake
    3. C. To build pressure in the tanks

    Answer: C — To build pressure in the tanks

    The compressor supplies the stored air that the whole braking system depends on.

18. 18. What does the air brake gauge tell the driver?

    1. A. The wear remaining in the brake linings
    2. B. The pressure available in the air reservoirs
    3. C. The temperature of the brake linings now

    Answer: B — The pressure available in the air reservoirs

    Reservoir pressure is what determines whether the brakes can be applied at full force.

19. 19. What is the purpose of an air dryer in the system?

    1. A. To remove moisture from the air
    2. B. To cool the compressed air
    3. C. To increase pressure

    Answer: A — To remove moisture from the air

    Moisture in the lines corrodes components and can freeze the system solid in cold weather.

20. 20. Why should you avoid fanning the brake pedal repeatedly on a downgrade?

    1. A. It overheats the pedal linkage
    2. B. It has no effect on air pressure
    3. C. It uses air faster than it is made

    Answer: C — It uses air faster than it is made

    Repeated applications drain the reservoirs, and losing air means losing the brakes entirely.

21. 21. What is the emergency function of a dual air brake system?

    1. A. It removes the need for a parking brake
    2. B. One circuit can still stop the vehicle
    3. C. It doubles the braking force

    Answer: B — One circuit can still stop the vehicle

    Separate front and rear circuits mean a single failure leaves partial braking rather than none.

22. 22. What should you do first when testing air brakes at the start of a trip?

    1. A. Build pressure to governor cut-out
    2. B. Apply the parking brake and drive forward
    3. C. Drain all the tanks

    Answer: A — Build pressure to governor cut-out

    Building to cut-out establishes a known starting point for the leakage and warning tests.

23. 23. How do you test that the low pressure warning works?

    1. A. Listen for the compressor cutting in
    2. B. Watch the tank drain valves
    3. C. Fan the pedal down and watch for it by 60 psi

    Answer: C — Fan the pedal down and watch for it by 60 psi

    The warning must be proven to work before the pressure reaches the danger level.

24. 24. How do you test that the spring brakes apply automatically?

    1. A. Turn the engine off and wait
    2. B. Confirm they set between 20 and 45 psi
    3. C. Apply the service brake firmly

    Answer: B — Confirm they set between 20 and 45 psi

    The automatic application is the last-resort safety function and must be verified.

25. 25. How is the parking brake tested?

    1. A. Set it and try to pull forward gently against it
    2. B. Apply it while moving at speed
    3. C. Release it on a hill and check for movement

    Answer: A — Set it and try to pull forward gently against it

    A gentle pull against the set brake proves it will actually hold the vehicle.

26. 26. How is the service brake tested before setting off?

    1. A. Press the pedal hard while parked
    2. B. Rev the engine and listen for air
    3. C. Move slowly and apply the pedal firmly

    Answer: C — Move slowly and apply the pedal firmly

    Pulling to one side or a delayed response both indicate a fault to be found before the trip.

27. 27. What forms can the low air pressure warning take?

    1. A. Only an audible alarm
    2. B. A light, a buzzer, or a flag
    3. C. Only a red light

    Answer: B — A light, a buzzer, or a flag

    A driver must know which warning their specific vehicle uses before it matters.