At what gauge pressure is applied pushrod stroke measured?
Manitoba Commercial overview
Manitoba Commercial: Air brake inspections, tests and brake adjustment
Inspecting linings, chambers, drums, lines, tanks and compressors, the low air warning, build-up, governor, leak, tractor protection and spring brake tests, tug tests, draining, measuring pushrod stroke, long-stroke chambers and the S endorsement.
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- Topic drill
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Study reference: MPI Air Brake Manual (02/2026), Ch. 9 Inspecting components, Ch. 10 Inspecting system operation, Ch. 11 Inspecting adjustment and Ch. 12 Checklists
All 16 questions in this test
Every question and its answer choices. The correct answers and explanations appear when you take the test above.
At what gauge pressure is applied pushrod stroke measured?
- 90 to 100 psi, engine off, pedal fully applied
- 120 psi with the engine running
- 60 psi with the spring brakes applied
- 20 psi with the pedal lightly pressed
Testing the tractor protection valve, you hold the pedal with the service line disconnected. What shows a defect?
- The low air warning staying off
- No air at all coming out of the trailer service line
- The gauge needle holding steady
- Air exhausting from the trailer service line
What is the maximum leak-test loss for a straight truck or bus in Manitoba?
- 1 psi per minute
- 4 psi per minute
- 3 psi per minute
- 6 psi per minute
Which brake lining condition is a defect?
- Lining thicker than the minimum
- Lining soaked with grease or oil
- Lining touching the drum when applied
- Lining clear of the drum when released
In the leak test, what is the maximum air loss in one minute for a tractor and one trailer?
- 1 psi
- 4 psi
- 6 psi
- 3 psi
What is a slack adjuster's effective length?
- Camshaft centre to clevis pin distance
- The distance between the two axles
- The diameter of the brake chamber
- The length of the pushrod when the brake is released
What is the adjustment limit for a standard type 30 clamp-type chamber?
- 1 3/8 in. (35 mm)
- 2 in. (51 mm)
- 2 1/2 in. (64 mm)
- 3 in. (76 mm)
When should you inspect the air compressor?
- With the engine at high idle
- While the compressor is pumping
- With the trailer supply valve open
- With the engine stopped
Adjusting a manual slack adjuster, what do you do after the lining meets the drum?
- Back off the bolt about a third of a turn
- Tighten it one more full turn to remove any slack
- Leave it tight against the drum
- Back it off two full turns
During the tractor protection test, the trailer supply valve must close before pressure drops below what?
- 60 psi
- 90 psi
- 45 psi
- 20 psi
In the build-up test, how long may pressure take to rise from 85 to 100 psi at 600–900 rpm?
- Five minutes or less
- Two minutes or less
- Ten minutes or less
- 30 seconds or less
In the low air warning test, when does the vehicle fail?
- If the gauge reads over 100 psi
- If it fails to activate at or above 55 psi
- If the warning activates when pressure is above 60 psi
- If the warning sounds at 90 psi
In the governor test, which cut-out reading is a defect?
- Cut-out at 140 psi
- Cut-out at 130 psi
- Cut-in at 105 psi
- Cut-out below 120 psi
When draining air tanks, which discharge should be reported?
- Clean air after the moisture drains
- Any oil, or a lot of moisture from non-supply tanks
- A short hiss when the valve opens
- A small amount of moisture from the supply tank only
Why must brake chambers on each end of a steering axle be the same size?
- So the spring brakes release sooner
- So both chambers can share one air line to save hose
- So braking is balanced and steering unaffected
- So the slack adjusters wear faster
How can you recognize a long-stroke brake chamber?
- A larger yellow knob in the cab
- Square ports, a trapezoid tag and markings
- Round air ports and no stroke tag on the clamp
- A blue clamp ring
Air brake inspections, tests and brake adjustment: 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 ↗
Ch. 9 Inspecting air brake components (pp. 26–28)
- Lining must touch the drum when applied and be clear when released; cracked, loose, missing, oil- or grease-soaked or too-thin lining is defective.
- Chamber size is the diaphragm area in square inches; both ends of an axle, especially a steering axle, need the same size.
- Check chambers for leaks with spring brakes released and service brakes applied; factory vent holes are normal.
- Slack adjuster effective length (camshaft centre to clevis pin) must match on each side of a steering axle.
- Air lines are defective when damage reaches the reinforcing or inner layer; improper fittings or repairs are prohibited.
- Tanks must be securely mounted; inspect the compressor with the engine stopped; a loose, cut or frayed belt is defective.
Ch. 10 Inspecting system operation (pp. 29–37)
- Low air warning: start above 90 psi with the ignition on, fan the brakes; it fails if it does not activate at or above 55 psi (major defect).
- Build-up: lower pressure below 80 psi, close the trailer supply valve, run at 600–900 rpm; 85 to 100 psi must take two minutes or less (minor defect if longer).
- Governor: cut-out must be 120–145 psi and cut-in at least 100 psi (minor defect otherwise).
- Leak test, engine off, brakes fully applied for one minute: no more than 3 psi for a straight truck, tractor or bus, 4 psi for a tractor and trailer, 6 psi with two or more trailers (major defect if exceeded).
- Tractor protection test: lines disconnected, open the trailer supply valve — it must close before 20 psi; then with the brake pedal held, no air may come from the service line.
- Trailer spring brakes must apply when the trailer supply valve is pulled out.
- Tug tests check that trailer and tractor spring brakes hold, the hand valve holds, and the service brakes stop the vehicle.
- Drain the supply tank first; a lot of moisture from other tanks, or any oil, must be reported; a faulty drain valve is a minor defect.
Ch. 11 Inspecting brake adjustment (pp. 38–40)
- Pushrod stroke must be inspected at least daily; the most common chamber size is 30.
- Long-stroke chambers have square air ports, a trapezoidal stroke tag and markings; standard chambers have round ports.
- Measure applied stroke with pressure above 90 psi, spring brakes released, gauges at 90–100 psi, engine off and the pedal fully applied.
- Any stroke over the adjustment limit is a major defect.
- In Manitoba only certified technicians and S-endorsed drivers may re-adjust manual slack adjusters; automatics needing regular adjustment are defective and go to a certified technician.
Ch. 12 Practical exam and S endorsement (pp. 41–48)
- Bring wheel chocks, a watch with a second hand, the chamber sizes and types, a way to hold the pedal, and tools to mark and measure the pushrod.
- To adjust a manual slack adjuster: press in the locking sleeve, turn the bolt until the lining meets the drum, then back off about a third of a turn and confirm the sleeve re-engages.
- A type 30 standard chamber's adjustment limit is 2 in. (51 mm); type 30 long-stroke is 2 1/2 in. (64 mm).
Study the Air brake inspections, tests and brake adjustment rules as flashcards →
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