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Commercial driver’s license (CDL) knowledge tests · California DMV

Inspecting Air Brake Systems

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Questions and answers

  1. If the air compressor is belt-driven, what do you check during the engine compartment check?

    The condition and tightness of the belt

    A belt-driven compressor needs a drive belt that is in good condition and tight.

    Section 5 · 5.3.1 – During Step 2 Engine ↗

  2. How do you prepare to check the slack adjusters on S-cam brakes?

    Park on level ground, chock the wheels, and release the parking brakes

    The parking brakes must be released so the slack adjusters can move, so the wheels are chocked on level ground.

    Section 5 · 5.3.2 – During Step 5 Walk Around ↗

  3. How do you check a slack adjuster by hand?

    Use gloves and pull hard on each slack adjuster you can reach

    Pull hard on each slack adjuster within reach, wearing gloves.

    Section 5 · 5.3.2 – During Step 5 Walk Around ↗

  4. How far may a slack adjuster move where the push rod attaches before it probably needs adjustment?

    About one inch

    Movement of more than about one inch means the brake probably needs adjustment.

    Section 5 · 5.3.2 – During Step 5 Walk Around ↗

  5. You pull on a slack adjuster and it moves about two inches where the push rod attaches. What does that mean?

    It probably needs adjustment

    More than about one inch of movement points to a brake that needs adjusting.

    Section 5 · 5.3.2 – During Step 5 Walk Around ↗

  6. What is the danger of too much brake slack?

    The vehicle can be very hard to stop

    Vehicles with too much brake slack can be very hard to stop.

    Section 5 · 5.3.2 – During Step 5 Walk Around ↗

  7. What is the most common problem found in roadside inspections?

    Out-of-adjustment brakes

    Brakes out of adjustment are the most common finding in roadside inspections.

    Section 5 · 5.3.2 – During Step 5 Walk Around ↗

  8. Vehicles built since what year all have automatic slack adjusters?

    1994

    All vehicles built since 1994 have automatic slack adjusters.

    Section 5 · 5.3.2 – During Step 5 Walk Around ↗

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

    Yes, they must be checked

    Automatic slack adjusters adjust themselves during full brake applications, but they must still be checked.

    Section 5 · 5.3.2 – During Step 5 Walk Around ↗

  10. When should automatic slack adjusters normally be adjusted by hand?

    Only during brake maintenance and when the slack adjusters are installed

    Automatic adjusters should not need manual adjustment except during maintenance and installation.

    Section 5 · 5.3.2 – During Step 5 Walk Around ↗

  11. On a vehicle with automatic adjusters, the pushrod stroke exceeds the legal brake adjustment limit. What does that indicate?

    A mechanical problem in the adjuster or related brake parts, or an improperly installed adjuster

    An over-limit stroke with automatic adjusters signals a mechanical problem or bad installation.

    Section 5 · 5.3.2 – During Step 5 Walk Around ↗

  12. Why is manual adjustment of automatic slack adjusters dangerous?

    It may give the driver a false sense of security about the brakes

    Manual adjustment usually masks a mechanical problem without fixing it.

    Section 5 · 5.3.2 – During Step 5 Walk Around ↗

  13. Brakes with automatic adjusters are found to be out of adjustment. What does the handbook recommend?

    Take the vehicle to a repair facility as soon as possible

    The underlying problem should be corrected at a repair facility as soon as possible.

    Section 5 · 5.3.2 – During Step 5 Walk Around ↗

  14. When is manual adjustment of an automatic adjuster acceptable?

    Only as a temporary measure in an emergency situation

    It is a temporary emergency measure, and the brake will likely soon be out of adjustment again.

    Section 5 · 5.3.2 – During Step 5 Walk Around ↗

  15. What is the likely result of routinely adjusting most automatic adjusters by hand?

    Premature wear of the adjuster itself

    Routine manual adjustment tends to wear out the adjuster early.

    Section 5 · 5.3.2 – During Step 5 Walk Around ↗

  16. What should be consulted before troubleshooting a brake adjustment problem on automatic slack adjusters?

    The specific manufacturer’s service manual

    Automatic slack adjusters from different makers do not all work the same way.

    Section 5 · 5.3.2 – During Step 5 Walk Around ↗

  17. Brake drums or discs must not have cracks longer than what?

    One half the width of the friction area

    Cracks longer than half the width of the friction area are not acceptable.

    Section 5 · Check Brake Drums (or Discs), Linings, and ↗

  18. At what thickness are brake linings considered worn dangerously thin?

    Less than 1/4 inch

    Linings thinner than 1/4 inch are dangerously worn.

    Section 5 · Check Brake Drums (or Discs), Linings, and ↗

  19. Which lining condition is a defect?

    Linings that are loose or soaked with oil or grease

    Linings must not be loose, soaked with oil or grease, or dangerously thin.

    Section 5 · Check Brake Drums (or Discs), Linings, and ↗

  20. What do you look for on the air hoses connected to the brake chambers?

    That they are not cut or worn due to rubbing

    Check the hoses for cuts and for wear from rubbing.

    Section 5 · Check Brake Drums (or Discs), Linings, and ↗

  21. During the CDL vehicle inspection test, you do not demonstrate a required air brake check or state its parameters correctly. What is the result?

    Automatic failure of the vehicle inspection portion of the skills test

    The items marked as required must be demonstrated and verbalized correctly, or the inspection portion is failed.

    Section 5 · 5.3.3 – Step 7: Final Air Brake Check ↗

  22. In what order must the required air brake checks be performed during the test?

    In any order, as long as they are performed correctly and effectively

    The checks may be done in any order if they are done correctly and effectively.

    Section 5 · 5.3.3 – Step 7: Final Air Brake Check ↗

  23. How does the applied leakage test begin?

    With the engine running and air pressure built to governor cut-out

    Start with the engine running and pressure built up to governor cut-out.

    Section 5 · 5.3.3.1 – Applied Leakage Test ↗

  24. What governor cut-out range does the handbook give for the applied leakage test?

    120–140 psi, or another level specified by the manufacturer

    Cut-out for this test is 120–140 psi unless the manufacturer specifies another level.

    Section 5 · 5.3.3.1 – Applied Leakage Test ↗

  25. In the applied leakage test, what do you do after cut-out and before applying the foot brake?

    Shut off the engine and release the parking brake

    Shut off the engine, chock the wheels if necessary, and release the parking brake, plus the tractor protection valve on a combination.

    Section 5 · 5.3.3.1 – Applied Leakage Test ↗

  26. In the applied leakage test, how long do you hold the foot brake after the air gauge stabilizes?

    1 minute

    The foot brake is held fully applied for 1 minute after the gauge stabilizes.

    Section 5 · 5.3.3.1 – Applied Leakage Test ↗

  27. What is the maximum air loss in the applied leakage test for a single vehicle?

    3 psi in one minute

    A single vehicle may lose no more than 3 psi in one minute with the brakes applied.

    Section 5 · 5.3.3.1 – Applied Leakage Test ↗

  28. What is the maximum air loss in the applied leakage test for a combination of 2 vehicles?

    4 psi in one minute

    A combination of 2 vehicles may lose no more than 4 psi in one minute with the brakes applied.

    Section 5 · 5.3.3.1 – Applied Leakage Test ↗

  29. What is the maximum air loss in the applied leakage test for a combination of 3 or more vehicles?

    6 psi in one minute

    A combination of 3 or more vehicles may lose no more than 6 psi in one minute with the brakes applied.

    Section 5 · 5.3.3.1 – Applied Leakage Test ↗

  30. An air-braked truck tows a trailer with electric or surge brakes. What is the maximum air loss in the applied leakage test?

    3 psi

    When the towed vehicles are not equipped with air brakes, the limit for the combination is 3 psi.

    Section 5 · 5.3.3.1 – Applied Leakage Test ↗

  31. Your tractor-trailer (2 vehicles, both with air brakes) loses 5 psi in one minute with the foot brake fully applied. What does that mean?

    The air loss is too much and repairs are needed before operating the vehicle

    The limit for a combination of 2 vehicles is 4 psi, so 5 psi shows a problem.

    Section 5 · 5.3.3.1 – Applied Leakage Test ↗

  32. Besides watching the air gauge during the applied leakage test, what else do you do?

    Listen for air leaks

    The driver checks the gauge for the pressure drop and listens for leaks.

    Section 5 · 5.3.3.1 – Applied Leakage Test ↗

  33. For the low air warning device test, in what position must the key be?

    “On” or “battery charge”

    The engine may be on or off, but the key must be in the on or battery charge position.

    Section 5 · 5.3.3.2 – Low Air Warning Device ↗

  34. How do you reduce the air pressure for the low air warning device test?

    Fan it off by rapidly applying and releasing the foot brake

    The pressure is fanned off with rapid applications and releases of the foot brake.

    Section 5 · 5.3.3.2 – Low Air Warning Device ↗

  35. Before what pressure must the low air warning devices (buzzer, light, and flag) activate during the test?

    Before air pressure drops below 55 psi, or the level specified by the manufacturer

    The warning must come on no lower than 55 psi or the manufacturer’s level.

    Section 5 · 5.3.3.2 – Low Air Warning Device ↗

  36. You are testing in a large bus whose warning comes on at 80–85 psi. What do you tell the examiner?

    The 55–75 psi parameter, and that your warning devices are designed to activate at a higher pressure

    State the standard parameters and explain that your bus is designed to warn at a higher pressure.

    Section 5 · 5.3.3.2 – Low Air Warning Device ↗

  37. The low air warning signal does not work. What is the danger in a single-circuit air system?

    You could lose air pressure without knowing it, causing sudden emergency braking

    Without a working warning, pressure can be lost unnoticed and the emergency brakes can come on suddenly.

    Section 5 · 5.3.3.2 – Low Air Warning Device ↗

  38. The low air warning signal does not work and pressure is lost. What is the effect in a dual system?

    The stopping distance will be increased

    In dual systems stopping distance increases, and only limited braking is possible before the spring brakes come on.

    Section 5 · 5.3.3.2 – Low Air Warning Device ↗

  39. Which vehicles must have both an audible and a visible low air warning device?

    Farm labor vehicles and Type I school buses

    Farm labor vehicles and Type I school buses need both kinds of warning.

    Section 5 · 5.3.3.2 – Low Air Warning Device ↗

  40. In the spring brake test, at what pressure should the valves normally close (pop out) as you fan off the air?

    Between 20 and 45 psi, or the level specified by the manufacturer

    The valves should pop out normally between 20 and 45 psi.

    Section 5 · 5.3.3.3 – Spring Brake Test ↗

  41. In the spring brake test on a tractor-trailer combination, which valves should close (pop out)?

    The tractor protection valve and the parking brake valve

    On a tractor-trailer both the tractor protection valve and the parking brake valve should pop out.

    Section 5 · 5.3.3.3 – Spring Brake Test ↗

  42. In the spring brake test on a single vehicle, which valve should close (pop out)?

    The parking brake valve

    On single vehicles and other combination types, the parking brake valve should pop out.

    Section 5 · 5.3.3.3 – Spring Brake Test ↗

  43. What position must the parking brake be in for the spring brake test?

    Released

    The parking brake, and the tractor protection valve on combinations, must be released while the driver fans off the air.

    Section 5 · 5.3.3.3 – Spring Brake Test ↗

  44. Your bus has an emergency park brake air tank, so the parking brake valve will not pop out. Which test must you perform?

    The spring brake test for triple reservoir vehicles

    Buses with an emergency park brake air tank use the triple reservoir test to check the spring brakes.

    Section 5 · 5.3.3.3 – Spring Brake Test ↗

  45. In the spring brake test for triple reservoir vehicles, how do you show that the spring brakes have activated?

    With the engine running, put the vehicle in a forward gear and attempt to drive forward

    The spring brakes should drag and keep the vehicle from easily moving forward.

    Section 5 · Spring Brake Test for Triple Reservoir ↗

  46. In the triple reservoir spring brake test, in what position do you leave the parking brake valve?

    Open (released)

    The valve stays in the open, released position, and wheel chocks are removed if necessary.

    Section 5 · Spring Brake Test for Triple Reservoir ↗

  47. In the triple reservoir test, the spring brakes do not keep the vehicle from easily moving forward. What happens?

    Your road test will be postponed

    Spring brakes that do not hold mean the road test is postponed.

    Section 5 · Spring Brake Test for Triple Reservoir ↗

  48. On which vehicles may the triple reservoir spring brake test be performed?

    Only single vehicles designed with an isolated parking brake reservoir

    Do not perform this test on combination vehicles.

    Section 5 · Spring Brake Test for Triple Reservoir ↗

  49. At what engine speed is the rate of air pressure buildup checked?

    Normal operating idle, typically 600–900 rpm

    The buildup check is done with the engine at normal operating idle.

    Section 5 · Check the Rate of Air Pressure Buildup ↗

  50. For dual air systems, how fast should pressure build from about 85 to 100 psi?

    Within 45 seconds

    In a dual system the pressure should rise from about 85 to 100 psi within 45 seconds.

    Section 5 · Check the Rate of Air Pressure Buildup ↗

  51. For single air systems in pre-1975 vehicles, how fast should pressure build from about 50 to 90 psi?

    Within 3 minutes

    In a single system the pressure should rise from about 50 to 90 psi within 3 minutes.

    Section 5 · Check the Rate of Air Pressure Buildup ↗

  52. At idle, your dual air system takes 2 minutes to build from 85 to 100 psi. What does that tell you?

    The pressure is not building at the proper rate

    A dual system should cover 85 to 100 psi within 45 seconds.

    Section 5 · Check the Rate of Air Pressure Buildup ↗

  53. How is the static leakage test set up?

    With a fully charged system, turn off the engine, release all brakes, and let the system settle

    With the engine off and all brakes released, wait for the gauge needle to stop moving and then time 1 minute.

    Section 5 · Static Leakage Test ↗

  54. What is the maximum air loss in one minute in the static leakage test for a single vehicle?

    2 psi

    With the brakes released, a single vehicle should not lose more than 2 psi in one minute.

    Section 5 · Static Leakage Test ↗

  55. What is the maximum air loss in one minute in the static leakage test for a combination of 2 vehicles?

    3 psi

    With the brakes released, a combination of 2 vehicles should not lose more than 3 psi in one minute.

    Section 5 · Static Leakage Test ↗

  56. What is the maximum air loss in one minute in the static leakage test for a combination of 3 or more vehicles?

    5 psi

    With the brakes released, a combination of 3 or more vehicles should not lose more than 5 psi in one minute.

    Section 5 · Static Leakage Test ↗

  57. In the static leakage test, what is the limit for a combination whose towed vehicles are not equipped with air brakes?

    2 psi

    If the towed vehicles have no air brakes, the static limit for the combination is 2 psi.

    Section 5 · Static Leakage Test ↗

  58. A single vehicle loses 3 psi in one minute with the engine off and all brakes released. Is that acceptable?

    No, the static limit for a single vehicle is 2 psi

    The 3 psi limit for a single vehicle applies with the brakes applied. With the brakes released the limit is 2 psi.

    Section 5 · Static Leakage Test ↗

  59. How do you test the parking brake?

    Set the parking brake and gently pull against it in a low gear

    Fasten your seat belt, set the parking brake, and pull gently against it in a low gear to see that it holds.

    Section 5 · Test Parking Brake ↗

  60. How do you test the service brakes?

    Move forward slowly at about 5 mph and apply the brakes firmly with the brake pedal

    With normal air pressure and the parking brake released, roll forward at about 5 mph and brake firmly.

    Section 5 · Test Service Brakes ↗

  61. What should you note during the service brake test?

    Any pulling to one side, unusual feel, or delayed stopping action

    Pulling, an unusual feel, or a delayed stop can reveal problems you would otherwise find only on the road.

    Section 5 · Test Service Brakes ↗

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