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Air-brake practice

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New Jersey Air-Brake practice questions

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Question 1 of 30
  1. 1. An air-braked truck has used some stored air during normal braking. Which component replenishes that supply?
  2. 2. A mechanic describes a device that tells the compressor when to resume pumping and when to stop adding air. Which device is being described?
  3. 3. If a truck's compressor stops working, what is the role of the air already held in the reservoirs?
  4. 4. A truck has manually operated air-tank drains. Why does the manual direct the driver to drain them completely at the end of each driving day?
  5. 5. An older air-brake system has an alcohol evaporator and manually drained tanks. Does maintaining the evaporator eliminate the need for tank drainage?
  6. 6. Air is escaping through the air system's safety relief valve. What should the driver recognize?
  7. 7. A driver repeatedly presses and releases the air-brake pedal when no braking is needed. What can this do to the air supply?
  8. 8. On an S-cam drum brake, what does rotation of the S-cam accomplish during a brake application?
  9. 9. A driver wants to know how much pressure is available in the air reservoirs, not how hard the brakes are being applied. Which instrument provides that information?
  10. 10. Under comparable conditions, a truck's application gauge shows that increasingly more pressure is needed to hold the same speed. What does that suggest?
  11. 11. While a spring-brake-equipped truck is operating normally, what keeps the powerful parking-brake springs from applying the brakes?
  12. 12. A spring-brake-equipped truck has badly out-of-adjustment wheel brakes. Why is it unsafe to rely on the spring brakes as a fully effective backup?
  13. 13. What makes a dual air-brake system different from one undivided air system?
  14. 14. Before moving a truck with dual air brakes, one gauge shows normal pressure but the other remains low. What should the driver do?
  15. 15. A truck's air compressor is driven by a belt. What belongs in the engine-compartment inspection for this arrangement?
  16. 16. Brakes with automatic slack adjusters repeatedly fall out of adjustment. Which response addresses the concern described in the manual?
  17. 17. During the air-brake walk-around, a hose leading to a brake chamber is worn where it rubs another part. How should the finding be treated?
  18. 18. A driver is checking the governor on a particular truck. What should determine the expected cut-in and cut-out pressures?
  19. 19. Two air-leakage observations were made: one with the foot brake released and one with it fully held down. Can their results simply be judged as the same test?
  20. 20. A dual-air truck has larger-than-minimum air reservoirs. Why consult its manufacturer's specifications when evaluating pressure buildup?
  21. 21. During a properly secured stationary low-pressure warning check, the engine is off and air pressure is being reduced as instructed. What electrical condition does the manual specify?
  22. 22. The low-air warning activates while an air-braked truck is moving. What is the appropriate immediate plan?
  23. 23. Why does planning a stop with air brakes include brake-lag distance in addition to perception, reaction, and braking distance?
  24. 24. A driver says that ABS guarantees a shorter stop on every road surface. What is the sound correction?
  25. 25. An ABS malfunction is identified, but the vehicle's conventional brake system has no other fault. What does loss of ABS by itself mean?
  26. 26. A bus is equipped with the described separate emergency reservoir for releasing its spring brakes after main-air loss. What limits its use?
  27. 27. A vehicle has a dashboard modulating valve specifically for its spring brakes. What function distinguishes that control?
  28. 28. A truck's air compressor has its own oil supply rather than engine-oil lubrication. What additional check does the manual call for before driving?
  29. 29. How does the air-brake system described in the manual signal brake application to drivers behind?
  30. 30. A parked vehicle has spring brakes applied and no reliable protection against compounding. Why avoid pressing its service-brake pedal at the same time?
Review all 30 questions with answers

  1. An air-braked truck has used some stored air during normal braking. Which component replenishes that supply?

    Correct answer: The air compressor

    The compressor pumps air into the reservoirs. Slack adjusters belong to the wheel-brake mechanism, while the stop-light switch signals braking to traffic behind.

    Source: New Jersey CDL Manual, March 2025 cover; Section 5, July 2017 footer, printed 5-1, physical 72 > 5.1.1 Air Compressor ↗

  2. A mechanic describes a device that tells the compressor when to resume pumping and when to stop adding air. Which device is being described?

    Correct answer: The compressor governor

    The governor responds to reservoir pressure and controls compressor pumping. The gauge displays pressure; the parking control performs a different job.

    Source: New Jersey CDL Manual, March 2025 cover; Section 5, July 2017 footer, printed 5-1, physical 72 > 5.1.2 Air Compressor Governor ↗

  3. If a truck's compressor stops working, what is the role of the air already held in the reservoirs?

    Correct answer: It provides a limited reserve for brake applications

    Stored air allows some brake applications even without new air from the compressor. It is a finite reserve, not permission to continue with a failed compressor.

    Source: New Jersey CDL Manual, March 2025 cover; Section 5, July 2017 footer, printed 5-1, physical 72 > 5.1.3 Air Storage Tanks ↗

  4. A truck has manually operated air-tank drains. Why does the manual direct the driver to drain them completely at the end of each driving day?

    Correct answer: Water and oil collect there, and retained water can freeze

    Water and compressor oil tend to collect at the bottom of air tanks. Removing them protects the system, including against water freezing in cold weather. This scenario is expressly about manual drains.

    Source: New Jersey CDL Manual, March 2025 cover; Section 5, July 2017 footer, printed 5-1, physical 72 > 5.1.4 Air Tank Drains ↗

  5. An older air-brake system has an alcohol evaporator and manually drained tanks. Does maintaining the evaporator eliminate the need for tank drainage?

    Correct answer: No; water and oil still need to be drained

    Where fitted, the evaporator helps reduce ice formation. It does not replace drainage of water and oil from tanks that lack automatic drain valves.

    Source: New Jersey CDL Manual, March 2025 cover; Section 5, July 2017 footer, printed 5-2, physical 73 > 5.1.5 Alcohol Evaporator ↗

  6. Air is escaping through the air system's safety relief valve. What should the driver recognize?

    Correct answer: A pressure-system fault needs mechanical attention

    The relief valve protects against excessive pressure. Its operation indicates a problem to have repaired, not a reason to defeat the protective valve.

    Source: New Jersey CDL Manual, March 2025 cover; Section 5, July 2017 footer, printed 5-2, physical 73 > 5.1.6 Safety Valve ↗

  7. A driver repeatedly presses and releases the air-brake pedal when no braking is needed. What can this do to the air supply?

    Correct answer: Use air faster than the compressor can replace it

    Each release exhausts some compressed air. Unnecessary cycling can deplete the reservoirs rather than replenish them.

    Source: New Jersey CDL Manual, March 2025 cover; Section 5, July 2017 footer, printed 5-2, physical 73 > 5.1.7 The Brake Pedal ↗

  8. On an S-cam drum brake, what does rotation of the S-cam accomplish during a brake application?

    Correct answer: It spreads the shoes against the inside of the drum

    The S-cam converts the linkage's movement into outward shoe movement against the drum. The question is about this brake design, not every type of air-operated brake.

    Source: New Jersey CDL Manual, March 2025 cover; Section 5, July 2017 footer, printed 5-2, physical 73 > 5.1.8 Foundation Brakes > S-cam Brakes ↗

  9. A driver wants to know how much pressure is available in the air reservoirs, not how hard the brakes are being applied. Which instrument provides that information?

    Correct answer: The supply-pressure gauge or gauges

    Supply gauges show reservoir pressure. An application gauge, where fitted, shows pressure being applied to the brakes instead.

    Source: New Jersey CDL Manual, March 2025 cover; Section 5, July 2017 footer, printed 5-2, physical 73 > 5.1.9 Supply Pressure Gauges ↗

  10. Under comparable conditions, a truck's application gauge shows that increasingly more pressure is needed to hold the same speed. What does that suggest?

    Correct answer: Possible brake fade, poor adjustment, or a leak

    Increasing application pressure for the same result is a warning sign. The manual lists fade as well as adjustment, leakage, and mechanical problems, so the gauge alone does not identify one exclusive cause.

    Source: New Jersey CDL Manual, March 2025 cover; Section 5, July 2017 footer, printed 5-3, physical 74 > 5.1.10 Application Pressure Gauge ↗

  11. While a spring-brake-equipped truck is operating normally, what keeps the powerful parking-brake springs from applying the brakes?

    Correct answer: Air pressure holds the springs back

    Air pressure holds spring brakes released. Removing that pressure lets the springs apply the brakes mechanically.

    Source: New Jersey CDL Manual, March 2025 cover; Section 5, July 2017 footer, printed 5-3, physical 74 > 5.1.14 Spring Brakes ↗

  12. A spring-brake-equipped truck has badly out-of-adjustment wheel brakes. Why is it unsafe to rely on the spring brakes as a fully effective backup?

    Correct answer: Their braking effectiveness also depends on proper adjustment

    Spring brakes do not cure poor brake adjustment. The manual warns that both regular braking and emergency/parking braking can be impaired.

    Source: New Jersey CDL Manual, March 2025 cover; Section 5, July 2017 footer, printed 5-3, physical 74 > 5.1.14 Spring Brakes ↗

  13. What makes a dual air-brake system different from one undivided air system?

    Correct answer: Separate air circuits use one set of driver brake controls

    A dual system has separate tanks, hoses, and lines for its two systems, operated through one set of controls. Do not assume every vehicle has the same exact axle assignment.

    Source: New Jersey CDL Manual, March 2025 cover; Section 5, July 2017 footer, printed 5-5, physical 76 > 5.2 Dual Air Brake ↗

  14. Before moving a truck with dual air brakes, one gauge shows normal pressure but the other remains low. What should the driver do?

    Correct answer: Wait for adequate pressure in both; investigate the low side

    Both halves of the dual system must be ready. A normal reading on one side does not establish that the other side can supply its brakes properly.

    Source: New Jersey CDL Manual, March 2025 cover; Section 5, July 2017 footer, printed 5-5, physical 76 > 5.2 Dual Air Brake ↗

  15. A truck's air compressor is driven by a belt. What belongs in the engine-compartment inspection for this arrangement?

    Correct answer: Check the belt's condition and tightness

    A belt-driven compressor depends on that drive belt. Inspect its condition and tightness; this additional check is conditional on the belt-driven design.

    Source: New Jersey CDL Manual, March 2025 cover; Section 5, July 2017 footer, printed 5-6, physical 77 > 5.3.1 During Step 2 Engine Compartment Checks ↗

  16. Brakes with automatic slack adjusters repeatedly fall out of adjustment. Which response addresses the concern described in the manual?

    Correct answer: Have the underlying fault diagnosed and repaired

    Repeated manual adjustment can mask a fault in an automatic adjuster or related components. The system needs qualified diagnosis using the manufacturer's service instructions, not a routine workaround.

    Source: New Jersey CDL Manual, March 2025 cover; Section 5, July 2017 footer, printed 5-6, physical 77 > 5.3.2 During Step 5 Walk-around Inspection > Check Slack Adjusters on S-cam Brakes ↗

  17. During the air-brake walk-around, a hose leading to a brake chamber is worn where it rubs another part. How should the finding be treated?

    Correct answer: As a brake-system defect needing attention

    The inspection specifically includes cut or rubbing-worn air hoses. A normal pressure reading at one moment does not make physical hose damage acceptable.

    Source: New Jersey CDL Manual, March 2025 cover; Section 5, July 2017 footer, printed 5-6, physical 77 > 5.3.2 During Step 5 Walk-around Inspection > Check Brake Drums (or Discs), Linings, and Hoses ↗

  18. A driver is checking the governor on a particular truck. What should determine the expected cut-in and cut-out pressures?

    Correct answer: The manufacturer's specifications for that system

    The manual gives approximate typical values but directs the driver to check the manufacturer's specifications. Treating a typical value as universal can misjudge the system.

    Source: New Jersey CDL Manual, March 2025 cover; Section 5, July 2017 footer, printed 5-6, physical 77 > 5.3.3 Step 7 Final Air Brake Check > Check Air Compressor Governor Cut-in and Cut-out Pressures ↗

  19. Two air-leakage observations were made: one with the foot brake released and one with it fully held down. Can their results simply be judged as the same test?

    Correct answer: No; test conditions and vehicle configuration matter

    The manual separates released-brake and applied-brake checks and distinguishes single from combination vehicles. A result must be matched to its actual setup; this item does not supply numerical limits or replace a complete test procedure.

    Source: New Jersey CDL Manual, March 2025 cover; Section 5, July 2017 footer, printed 5-7, physical 78 > 5.3.3 Step 7 Final Air Brake Check > Test Air Leakage Rate (continued from printed 5-6) ↗

  20. A dual-air truck has larger-than-minimum air reservoirs. Why consult its manufacturer's specifications when evaluating pressure buildup?

    Correct answer: The larger tanks can take longer to fill without indicating a fault

    The manual expressly allows that larger-than-minimum tanks may have a longer safe buildup time. It does not say that slow buildup can always be ignored.

    Source: New Jersey CDL Manual, March 2025 cover; Section 5, July 2017 footer, printed 5-7, physical 78 > 5.3.3 Step 7 Final Air Brake Check > Check Rate of Air Pressure Buildup ↗

  21. During a properly secured stationary low-pressure warning check, the engine is off and air pressure is being reduced as instructed. What electrical condition does the manual specify?

    Correct answer: Electrical power is on

    The warning check is performed with the engine off but electrical power on. This question isolates that condition; it is not the complete preparation or pressure-threshold procedure.

    Source: New Jersey CDL Manual, March 2025 cover; Section 5, July 2017 footer, printed 5-7, physical 78 > 5.3.3 Step 7 Final Air Brake Check > Test Low Pressure Warning Signal ↗

  22. The low-air warning activates while an air-braked truck is moving. What is the appropriate immediate plan?

    Correct answer: Stop and safely park as soon as possible while control remains

    The remaining air allows controlled braking only for a limited time. Stop safely before it is exhausted rather than waiting for automatic spring-brake application.

    Source: New Jersey CDL Manual, March 2025 cover; Section 5, July 2017 footer, printed 5-9, physical 80 > 5.4.7 Low Air Pressure ↗

  23. Why does planning a stop with air brakes include brake-lag distance in addition to perception, reaction, and braking distance?

    Correct answer: Air takes time to travel through the system and apply the brakes

    Brake lag is the system response time after pedal application. The manual includes it as an additional stopping-distance component; no universal time or distance is assumed here.

    Source: New Jersey CDL Manual, March 2025 cover; Section 5, July 2017 footer, printed 5-8, physical 79 > 5.4.4 Stopping Distance ↗

  24. A driver says that ABS guarantees a shorter stop on every road surface. What is the sound correction?

    Correct answer: ABS helps prevent lockup but does not guarantee a shorter stop

    ABS is intended to help maintain control by preventing wheel lockup. That benefit is not a promise of shorter stopping distance in every situation.

    Source: New Jersey CDL Manual, March 2025 cover; Section 5, July 2017 footer, printed 5-4, physical 75 > 5.1.16 Antilock Braking Systems (ABS) ↗

  25. An ABS malfunction is identified, but the vehicle's conventional brake system has no other fault. What does loss of ABS by itself mean?

    Correct answer: Regular braking remains, but the ABS needs service

    ABS is an addition to the regular brake system. Losing its assistance does not by itself eliminate regular braking; the malfunction still needs attention. This is not clearance to drive a vehicle with other brake defects.

    Source: New Jersey CDL Manual, March 2025 cover; Section 5, July 2017 footer, printed 5-8, physical 79 > 5.4.2 Braking with Antilock Brakes ↗

  26. A bus is equipped with the described separate emergency reservoir for releasing its spring brakes after main-air loss. What limits its use?

    Correct answer: The reserve can release the brakes only a limited number of times

    This optional arrangement provides only a limited reserve for emergency movement. It is not a universal bus feature or a repair of the failed main system.

    Source: New Jersey CDL Manual, March 2025 cover; Section 5, July 2017 footer, printed 5-4, physical 75 > 5.1.15 Parking Brake Controls > Dual Parking Control Valves ↗

  27. A vehicle has a dashboard modulating valve specifically for its spring brakes. What function distinguishes that control?

    Correct answer: It allows the spring brakes to be applied gradually

    On vehicles equipped with this feature, moving the lever changes the spring-brake application. The question identifies its function, not a universal emergency-braking maneuver.

    Source: New Jersey CDL Manual, March 2025 cover; Section 5, July 2017 footer, printed 5-3, physical 74 > 5.1.15 Parking Brake Controls > Modulating Control Valves ↗

  28. A truck's air compressor has its own oil supply rather than engine-oil lubrication. What additional check does the manual call for before driving?

    Correct answer: Check the compressor's oil level

    Some compressors have a separate oil supply, while others use engine oil. The inspection must match the actual compressor design.

    Source: New Jersey CDL Manual, March 2025 cover; Section 5, July 2017 footer, printed 5-1, physical 72 > 5.1.1 Air Compressor ↗

  29. How does the air-brake system described in the manual signal brake application to drivers behind?

    Correct answer: Air pressure operates an electrical stop-light switch

    A pressure-operated electrical switch turns on the brake lights during air-brake application. This is a component-function question, not a substitute for checking the lamps.

    Source: New Jersey CDL Manual, March 2025 cover; Section 5, July 2017 footer, printed 5-3, physical 74 > 5.1.12 Stop Light Switch ↗

  30. A parked vehicle has spring brakes applied and no reliable protection against compounding. Why avoid pressing its service-brake pedal at the same time?

    Correct answer: Combined spring and air forces can damage the brakes

    Some systems protect against combined application forces, but not all do and protection may fail. The manual advises avoiding the habit of pressing the service pedal while the spring brakes are applied.

    Source: New Jersey CDL Manual, March 2025 cover; Section 5, July 2017 footer, printed 5-3, physical 74 > 5.1.15 Parking Brake Controls > Caution ↗

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Home / New Jersey / CDL

Air-brake practice

30 original questions on air systems, inspections and warning signs. This is a study selection, not an endorsement or the official test length.

All topics and study tools

These are the same 30 records used in the two short sets. Use the official manual, Section 5 and qualified hands-on training for complete inspection procedures. Vehicle designs and manufacturer specifications matter. This selection does not cover every pressure threshold or substitute for practical training.