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Alabama Air Brakes Test – 20 Questions with Answers

Test your knowledge of air brake systems with 20 practice questions covering air brake components, pressure, warning systems, air leaks, brake lag, spring brakes, air tanks, and safe inspection procedures for commercial drivers.

20
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15 min
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Medium
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  1. 1. What is the main purpose of an air brake system on a commercial motor vehicle?

    • A. To cool the engine
    • B. To use compressed air to operate the vehicle's brakes
    • C. To increase engine power
    • D. To control the steering system
    Show answer

    B. To use compressed air to operate the vehicle's brakes

    Air brake systems use compressed air to transmit braking force to the vehicle's brake components.

  2. 2. Which component compresses air and pumps it into the air storage tanks?

    • A. Air compressor
    • B. Brake chamber
    • C. Slack adjuster
    • D. Governor
    Show answer

    A. Air compressor

    The air compressor generates compressed air and supplies it to the vehicle's air reservoirs.

  3. 3. What is the function of the air compressor governor?

    • A. It applies the parking brakes
    • B. It controls when the compressor pumps air
    • C. It increases brake shoe friction
    • D. It drains moisture from the tanks
    Show answer

    B. It controls when the compressor pumps air

    The governor controls the compressor's loading and unloading by determining when it should pump air into the reservoirs.

  4. 4. What is the purpose of air tanks or reservoirs?

    • A. To store compressed air
    • B. To store engine oil
    • C. To cool brake drums
    • D. To control tire pressure
    Show answer

    A. To store compressed air

    Air reservoirs store compressed air so it is available when the braking system requires it.

  5. 5. Why are air tanks equipped with drain valves?

    • A. To remove accumulated water and compressor oil
    • B. To increase engine speed
    • C. To increase tire pressure
    • D. To release brake pressure while driving
    Show answer

    A. To remove accumulated water and compressor oil

    Moisture and oil can accumulate in air reservoirs and should be drained to help maintain the air brake system.

  6. 6. What does the low-air-pressure warning signal indicate?

    • A. The engine temperature is too high
    • B. Air pressure in the system is dangerously low
    • C. The fuel tank is empty
    • D. The parking brake has been released
    Show answer

    B. Air pressure in the system is dangerously low

    A low-air warning alerts the driver that air pressure has fallen to a dangerous level and immediate action may be required.

  7. 7. At what approximate pressure must a low-air warning signal activate on a typical air brake system?

    • A. 20 psi
    • B. 40 psi
    • C. 60 psi
    • D. 100 psi
    Show answer

    C. 60 psi

    Federal requirements generally require the low-air warning to activate before pressure drops below 60 psi on vehicles equipped with air brakes.

  8. 8. What happens when the air pressure in a spring brake system becomes very low?

    • A. The spring brakes can apply automatically
    • B. The steering wheel locks
    • C. The engine automatically stops
    • D. The headlights turn off
    Show answer

    A. The spring brakes can apply automatically

    Spring brakes are held in the released position by air pressure. If pressure is lost, the powerful springs can apply the brakes.

  9. 9. What is the main function of a brake chamber?

    • A. To convert air pressure into mechanical force for braking
    • B. To store diesel fuel
    • C. To cool the brake drums
    • D. To generate compressed air
    Show answer

    A. To convert air pressure into mechanical force for braking

    Air pressure pushes a diaphragm or piston in the brake chamber, producing mechanical movement that applies the brakes.

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

    • A. The time required for air to reach the brake components after the brake pedal is applied
    • B. The time required to refuel the vehicle
    • C. The time required to replace a tire
    • D. The time required for the engine to start
    Show answer

    A. The time required for air to reach the brake components after the brake pedal is applied

    Unlike hydraulic brakes, air brakes have a slight delay because compressed air must travel through the system before the brakes apply.

  11. 11. What is the purpose of slack adjusters?

    • A. To adjust the distance between the brake shoes and drum
    • B. To store compressed air
    • C. To regulate engine oil
    • D. To cool the tires
    Show answer

    A. To adjust the distance between the brake shoes and drum

    Slack adjusters transfer braking force and help maintain the correct clearance between brake components.

  12. 12. What should you check for during an air brake inspection?

    • A. Air leaks and damaged or worn components
    • B. Only the color of the brake drums
    • C. Only the engine oil level
    • D. Only the windshield condition
    Show answer

    A. Air leaks and damaged or worn components

    A proper air brake inspection includes checking for leaks, damaged components, excessive wear, and other conditions that could affect braking performance.

  13. 13. If the air pressure drops rapidly while the vehicle is parked with the brakes released, what could this indicate?

    • A. An air leak
    • B. A full fuel tank
    • C. Normal tire inflation
    • D. A properly functioning compressor
    Show answer

    A. An air leak

    A rapid loss of air pressure can indicate a leak in the air brake system and should be investigated before operating the vehicle.

  14. 14. Why should you avoid repeatedly pumping the brake pedal when driving a vehicle with air brakes?

    • A. It can use up compressed air
    • B. It increases fuel tank capacity
    • C. It makes the tires larger
    • D. It increases engine oil pressure
    Show answer

    A. It can use up compressed air

    Repeatedly pumping the brake pedal can consume stored air and reduce system pressure, especially when the compressor cannot replace the air quickly enough.

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

    • A. Continue normally until the destination
    • B. Ignore the warning if the brakes still work
    • C. Stop safely as soon as possible and determine the cause
    • D. Turn off the warning device
    Show answer

    C. Stop safely as soon as possible and determine the cause

    A low-air warning indicates a potentially serious brake-system problem. The vehicle should be brought to a safe stop and the problem addressed.

  16. 16. What is the purpose of spring brakes on a commercial vehicle?

    • A. They provide parking and emergency braking
    • B. They increase engine horsepower
    • C. They cool the air compressor
    • D. They inflate the tires
    Show answer

    A. They provide parking and emergency braking

    Spring brakes use mechanical spring force and are commonly used for parking and as an emergency braking system when air pressure is lost.

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

    • A. To remove moisture from compressed air
    • B. To increase engine temperature
    • C. To lubricate brake shoes
    • D. To increase tire pressure
    Show answer

    A. To remove moisture from compressed air

    An air dryer removes moisture and contaminants from compressed air before it enters the air brake system's reservoirs.

  18. 18. What is a safe practice when descending a long or steep grade in a heavy vehicle equipped with air brakes?

    • A. Rely only on continuous service braking
    • B. Select an appropriate lower gear and use proper braking techniques
    • C. Shift into neutral
    • D. Turn off the engine
    Show answer

    B. Select an appropriate lower gear and use proper braking techniques

    Using an appropriate lower gear and proper braking techniques helps control speed and reduces the risk of overheating the service brakes.

  19. 19. Why is proper air pressure important before operating a vehicle with air brakes?

    • A. The braking system depends on adequate air pressure to operate correctly
    • B. It prevents the radio from working
    • C. It increases the vehicle's top speed
    • D. It eliminates the need for brake inspections
    Show answer

    A. The braking system depends on adequate air pressure to operate correctly

    Adequate air pressure is essential for the proper operation of service and spring brake systems.

  20. 20. What should a driver do if an air brake system fails to build or maintain adequate pressure during the pre-trip inspection?

    • A. Operate the vehicle slowly
    • B. Drive only on local roads
    • C. Have the problem corrected before operating the vehicle
    • D. Pump the brake pedal continuously while driving
    Show answer

    C. Have the problem corrected before operating the vehicle

    An air brake system that cannot build or maintain adequate pressure may not provide safe braking performance and should be repaired before the vehicle is operated.