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Ontario Class D (DZ) overview

Ontario Class D (DZ): Brake checks: hydraulic and air

Testing hydraulic brakes with and without power assist, brake fluid limits, and the straight-truck air checks: build-up, air loss of 3 psi, low-air warning, pushrod stroke and spring brakes.

  • 19 questions
  • Topic drill
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Brake checks: hydraulic and air · Question 1Score 0/0

What are truck drivers expected to know about a disabled brake system?

Study reference: MTO Truck Handbook (online edition, 2026), Ch. 2 Driving — classes A and D — Brake inspection

All 19 questions in this test

Every question and its answer choices. The correct answers and explanations appear when you take the test above.

  1. What are truck drivers expected to know about a disabled brake system?

    1. How to rebuild it at roadside
    2. Recognize it, not repair it
    3. How to bypass it safely
    4. Nothing; mechanics only

  2. You start the engine while holding the pedal, and the pedal does not drop at all. What does it mean?

    1. No assist; take it out of service
    2. The brake fluid level is too high
    3. The brakes are perfectly adjusted
    4. This is normal for a cold engine

  3. Which handbook should you use for a full air brake pre-trip inspection?

    1. The CVOR operator's manual
    2. The Official Air Brake Handbook
    3. The Bus Handbook
    4. The Official Driver's Handbook

  4. Checking power-assisted hydraulic brakes, what do you do first with the engine stopped?

    1. Open the bleed screws
    2. Set the parking brake twice
    3. Hold the pedal down hard
    4. Pump the pedal several times

  5. How can brakes cause a truck fire?

    1. By being painted the wrong colour
    2. By overheating
    3. By using brand-new brake linings
    4. By being washed too often

  6. What can happen to the operator if a truck is found with out-of-adjustment brakes?

    1. Their insurance is cancelled at once
    2. Nothing; only the driver is fined
    3. They receive a free inspection
    4. Their CVOR certificate may be suspended

  7. Why is fanning the brakes dangerous on a long downgrade?

    1. It can drop air below safe levels
    2. It locks the steering column
    3. It turns on the ABS warning lamp
    4. It overheats the engine oil quickly

  8. At what air pressure should pushrod stroke be measured?

    1. 90 to 100 psi
    2. Any pressure at all
    3. 40 to 50 psi
    4. 120 to 130 psi

  9. During the air-loss test, what range must system pressure be in?

    1. Below 60 psi
    2. Above the safety valve setting
    3. Between cut-in and cut-out
    4. Exactly 150 psi

  10. Your truck has air disc brakes behind body panels. How is pushrod stroke checked on the road test?

    1. You remove the wheels to reach them
    2. You explain it verbally
    3. You skip all the brake items entirely
    4. The road test is cancelled on the spot

  11. During the air-loss test, what must you do with the spring (parking) brakes?

    1. Apply them
    2. Cage them
    3. Release them
    4. Leave the knob halfway

  12. Air pressure drops toward 60 psi while you drive. What will the spring brakes do?

    1. Do nothing until 20 psi
    2. Release completely and stay off
    3. Begin to apply on their own
    4. Lock the steering wheel

  13. On an air-brake dump truck, what must happen before you drive away?

    1. The ABS lamp must stay lit while moving
    2. All air tanks must be fully drained
    3. The engine must first reach 2,000 rpm
    4. Enough air; low-air warning off

  14. The low-air warning comes on at 50 psi. How is this classed?

    1. A minor defect
    2. Not a defect if the buzzer works
    3. A major defect
    4. Normal operation

  15. Testing the low-air warning, what must you do with the ignition key?

    1. Turn it to start and hold
    2. Remove it
    3. Turn it on
    4. Nothing; it does not matter

  16. Testing air build-up, how far must pressure rise and in what time?

    1. 60 to 80 psi within 10 minutes
    2. 85 to 100 psi within 2 minutes
    3. 0 to 60 psi within 30 seconds
    4. 100 to 145 psi within 5 minutes

  17. On hydraulic brakes without power assist, what result means the truck must come out of service?

    1. The brake light comes on
    2. The pedal returns quickly
    3. The held pedal sinks steadily
    4. The pedal feels firm and stays up

  18. Before timing the air build-up, how low do you first pump the pressure?

    1. To zero
    2. To 100 psi
    3. To 60 psi exactly
    4. To 80 psi or less

  19. You hear an air leak during your circle check. What should you do next?

    1. Ignore it if pressure is normal
    2. Drive and recheck tomorrow
    3. Do the air-loss rate test
    4. Add an alcohol evaporator

Brake checks: hydraulic and air: key rules to remember

Our summary of what the official handbook says on this topic, in our own words. Read it before or after the practice questions above, then check the original chapter. Read the official chapter ↗

Hydraulic brakes with power assist

  • Drivers are not expected to repair brakes but must recognize when they are not working properly.
  • With the engine off, pump the pedal several times to use up the power assist, then apply moderate pressure.
  • Start the engine: the pedal should drop slightly and then stop.
  • If the pedal keeps dropping, or does not drop at all (no power assist), stop the engine; the vehicle must be taken out of service and inspected professionally.

Hydraulic brakes without power assist

  • Apply moderate pressure and hold it.
  • A steady drop of the pedal means the vehicle must be taken out of service for professional inspection.

Air-brake trucks

  • Before moving, the air gauge must show enough pressure and the low-air buzzer or light must have stopped.
  • For more detail on air brakes, the truck handbook refers you to the Official MTO Air Brake Handbook.

Air brake items on a straight truck

  • Build-up rate: with the engine at 600–900 rpm, pressure must rise from 85 to 100 psi within two minutes; slower is a minor defect.
  • To test build-up, first pump the brakes to bring pressure down to 80 psi or less.
  • Any air leak you can hear is a minor defect; when you hear one, do the air-loss test.
  • Air-loss test: chock the wheels, release the spring brakes, have pressure between cut-in and cut-out (80–145 psi), shut off the engine, hold the pedal fully applied and watch the gauges for one minute after the initial drop settles.
  • A straight truck fails (major defect) if pressure drops more than 3 psi (21 kPa) in that minute.
  • Low-air warning test: start above 90 psi with the key on, pump the pedal down and note when the warning comes on; it is a major defect if it fails or activates below 55 psi.
  • Pushrod stroke is checked with air at 90–100 psi, the engine off and the brakes fully applied; a stroke past the adjustment limit is a major defect.
  • Vehicles with air disc brakes, low bodies or covering panels may not allow stroke measurement; the examiner then asks you to explain the check.

Spring brakes and low air

  • Spring brakes apply automatically when system pressure drops below a set level, normally 60 psi (414 kPa).
  • If the low air-pressure warning activates at any time, stop immediately in the safest place and correct the air loss before going on.
  • Fanning the brakes on a long downgrade can drop the air pressure below what the brakes need.

Brake adjustment

  • Brakes out of adjustment are unsafe, can get the vehicle detained, and can put the operator's CVOR certificate at risk.
  • You cannot adjust your own air brakes unless you passed an approved adjustment course or are a certified mechanic.
  • Do a full air brake pre-trip inspection, as described in the air brake handbook, before the day's trip.

Brake heat

  • Overheated brakes, from misuse or poor adjustment, are a common cause of truck fires; check hub temperatures whenever you check tires.

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