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Ontario Air Brake (Z) overview

Air brake study guide: key rules on all 12 topics

Free Ontario Air Brake (Z) study guide: 238 key points from the The Official Air Brake Handbook (MTO) in plain words, organised by topic, each topic linked to its practice questions.

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  • 12 topics
  • 238 key points
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This study guide collects our notes on every topic of the Ontario Air Brake (Z) Endorsement Knowledge Test on one page: 238 short points in our own words, grouped by topic and by handbook section. Read it from top to bottom before your first practice test, or jump to a topic from the list below.

Each topic ends with a link to its practice questions, so you can check what you just read straight away, and a link to the official chapter for the full wording. The notes summarise the The Official Air Brake Handbook (MTO) from the Ontario Ministry of Transportation (MTO); they do not replace it, and where our notes and the official source differ, the official source wins.

Study these notes as flashcards →

How vehicle brakes work

Friction and heat, brake fade, why air brakes are used on large vehicles, the built-in application delay, drum versus disc brakes and which systems need a Z endorsement.

Practise How vehicle brakes work questionsFlashcardsOfficial chapter

Stopping a vehicle

  • Brakes stop a vehicle by pressing shoes or pads against drums or rotors; the friction turns the vehicle's motion into heat.
  • Too much heat causes brake fade, brake failure and even tire fires.
  • An overheated drum expands and can move away from the shoe so the brake no longer contacts it.
  • If brakes overheat from overuse or poor adjustment, stop, let them cool and check all brakes and their adjustment.
  • Make sure brake parts are cool to the touch before taking any measurements.
  • One malfunctioning brake makes all the others work harder, so they overheat and may fail too.

Air brakes versus hydraulic brakes

  • Hydraulic brakes use brake fluid, which cannot be compressed, so force reaches each wheel immediately; they are used on almost all cars and light trucks.
  • Air brakes use compressed air stored in tanks; they suit large commercial vehicles because they transmit high forces over long distances with simple parts.
  • Every air brake system has a split-second delay between pressing or releasing the pedal and the brakes reacting, while air moves through the system.
  • Special valves keep that delay as short as possible, but it never disappears.

Brake types at the wheels

  • Air-braked vehicles use either drum brakes (shoes and linings pushing outward against a drum) or disc brakes (pads in a caliper clamping both sides of a rotor).
  • The brake hardware at the wheels is called the foundation brake components.

Other systems and the Z endorsement

  • Air-over-hydraulic brakes, used mainly on medium-duty trucks, combine compressed air with a hydraulic system; in Ontario you need a Z endorsement to drive them.
  • Air parking brakes (air-operated parking brake with hydraulic service brakes), found on some medium-duty vehicles such as school buses, do not require a Z endorsement.

Foundation brakes

S-cam, disc and wedge brakes: the parts inside and outside the wheel, how the camshaft, slack adjuster and pushrod work, and which designs adjust themselves.

Practise Foundation brakes questionsFlashcardsOfficial chapter

Overview

  • Foundation brakes are the mechanical parts in and around the wheels that the air system operates; the rest of the system is built on them.
  • There are three types: "S" cam brakes, disc brakes and wedge brakes; one vehicle can use more than one type.

"S" cam brakes

  • The S-cam drum brake is the most common foundation brake on air-braked commercial vehicles.
  • Pushrod stroke from the brake chamber moves the slack adjuster on the end of the camshaft; the camshaft turns and its S-shaped head forces the shoes apart against the drum.
  • The exposed pushrod is a feature of S-cam brakes and makes it easy to check adjustment.
  • Inside the wheel: shoes and drum, the brake spider (main mounting base for the shoes), anchor pins and anchor springs, the camshaft head, camshaft rollers, and a return spring that pulls the shoes back and keeps the rollers on the cam.
  • Outside and easier to see: brake chamber and brackets, slack adjuster, pushrod, the camshaft shaft with its support brackets and bushings, dust shields or backing plates, and the drums.
  • Dust shields and backing plates protect parts inside the wheel but make them hard to see.

Disc brakes

  • Air disc brakes use calipers and rotors; the rotor is only partly visible behind the wheel, caliper and shields.
  • Pushrod stroke presses the brake pads against the rotor; some designs have exposed linkage and a slack adjuster.
  • Components: rotors, calipers, pads, slack adjusters and brake chambers.

Wedge brakes

  • Wedge brakes are drum brakes with no exposed linkage; the chambers point inward toward the shoes.
  • The pushrod slides a wedge between the shoes, pushing them outward against the drum.
  • Wedge brakes are designed to adjust themselves.
  • Components: drums, shoes and linings, spiders, dust shields and brake chambers.

Air supply subsystem

Compressor, governor cut-in and cut-out, the 80 to 145 psi operating range, wet and dry tanks, draining, air dryers, alcohol evaporators, safety valves and low-air warnings.

Practise Air supply subsystem questionsFlashcardsOfficial chapter

Compressor and governor

  • The air supply subsystem produces, stores and manages the compressed air the brakes use.
  • The engine-driven air compressor squeezes air into a smaller space, raising its pressure; compressed air is stored energy.
  • Compressors are driven directly by the engine or by belts and pulleys, and mounted on the engine or with brackets and fasteners that must stay secure.
  • The compressor turns whenever the engine runs; the governor tells it when to stop pumping (cut-out) and when to start again (cut-in).
  • Pressure is measured in kilopascals (kPa) or pounds per square inch (psi).

Normal pressure range

  • Cut-out is normally 20 to 25 psi (138–173 kPa) above cut-in.
  • A typical operating range is about 100 to 120 psi (690–828 kPa).
  • Actual cut-out must never be above 145 psi (1000 kPa); actual cut-in must never be below 80 psi (552 kPa).
  • Drive only when pressure is in the normal range; a drop below the normal cut-in point signals a malfunction or abnormal demand, so stop safely as soon as possible.
  • Abnormal readings should be confirmed by a technician with an accurate gauge.

Air tanks

  • Tanks are usually steel cylinders with domed ends under or around the frame; a vehicle may have one, two, three or more, and two tanks can share one shell with an internal divider.
  • Moisture condenses as air is compressed, and compressor oil can mix in; both settle at the bottom of the tanks.
  • The first tank, the supply or "wet" tank, collects most of the moisture and oil.
  • Sludge from moisture and oil can damage seals and make valves stick; the mixture can corrode tanks; moisture can freeze and cause brake failure; buildup reduces air volume.
  • One-way check valves stop air flowing back into the supply tank.
  • From the supply tank air splits into primary and secondary (dual-service, "dry") tanks; if one circuit fails, the other can still stop the vehicle.

Draining

  • Many manufacturers recommend draining the tanks daily through the drain valve at the bottom of each tank.
  • Always drain the supply (wet) tank first, so its moisture cannot flow into the next tank.
  • Check that each tank drains fully and watch the discharge for anything abnormal.
  • Vehicles with air dryers still need their tanks drained regularly.

Air dryer and alcohol evaporator

  • An air dryer sits between the compressor and the supply tank; air cools and passes through a drying material there.
  • The dryer expels the collected moisture with a burst of air when the compressor reaches cut-out.
  • An alcohol evaporator adds alcohol vapour to the air to lower the chance of moisture freezing; only products made for it may be used.

Gauges, safety valve, warnings

  • Every air-braked vehicle must have working air gauges on the dash, either two gauges (primary and secondary) or one gauge with two needles, in kPa or psi.
  • Safety valves on the supply tank and air dryer normally open at 150 psi (1035 kPa) if the governor fails; a venting safety valve needs immediate repair.
  • The low air-pressure warning must come on before pressure in either tank falls to 55 psi (380 kPa); most activate at 60 psi (414 kPa) or higher.
  • The warning must be visual (a light) and may also sound a buzzer, bell or alarm; a "wig wag" arm drops into the driver's view on some vehicles.
  • A low-air warning means a serious brake hazard: stop safely as soon as possible.

Compressed air hazards

  • Exhausting air moves fast and carries moisture, oil, dirt and dust that can hurt eyes and hearing.
  • Air exhausts at brake valve ports, near the axles, at the air dryer exhaust and at tank drain valves.
  • Never dismantle, remove, repair or tamper with any brake component.

Service brakes and brake chambers

The foot valve and dual circuits, front wheel-limiting valves, service brake chambers, pushrods, slack adjusters and why stroke must stay within the adjustment limit.

Practise Service brakes and brake chambers questionsFlashcardsOfficial chapter

Separate systems

  • Air-braked vehicles must have separate, independently controlled systems for normal stopping (service brakes) and for parking and emergency braking.

Brake pedal

  • Pressing the brake pedal (foot valve) sends compressed air to the service brakes; pressing harder opens the valve further, delivering more pressure and more braking force.
  • Most systems are dual circuit: air comes from both primary and secondary tanks to specific wheels, which vary by manufacturer.
  • If one circuit fails, the wheels on the other circuit still brake.
  • A front wheel-limiting valve reduces service brake force on the front steering axle.

Hoses and tubes

  • Many flexible hoses and tubes carry air; each must be the correct size and type.
  • Newer vehicles follow an industry colour code for lines; older vehicles may not.

Brake chambers

  • Air brake chambers are round metal containers at each wheel that turn air pressure into mechanical force.
  • A service brake chamber holds a rubber diaphragm, a pushrod and a return spring; air pushes the diaphragm, which pushes the pushrod out to apply the brake; the spring returns it when air is released.
  • The pushrod and a lever called the slack adjuster link the chamber to the brake assembly.
  • Pushrod stroke is how far the pushrod travels out of the chamber; on most designs it can be measured and compared with the adjustment limit.
  • Stroke grows with application pressure: going from 10 psi to 80 psi of application increases it noticeably.
  • Each chamber has a limited stroke capacity; past it, the chamber produces no braking force.
  • As linings wear, the linkage must be readjusted so stroke stays in the normal range; brake force drops sharply once stroke passes the adjustment limit.
  • Any brake past its adjustment limit is a defect needing prompt attention; only certified technicians (or drivers certified for manual slack adjusters) may readjust brakes.
  • Most commercial vehicles use clamp-type chambers, held together with a clamp; correct chamber size and type determine the adjustment limit.

Spring (parking and emergency) brakes

How spring brakes apply when air is lost, the 60 psi release pressure, the yellow and blue control knobs, caged chambers and DD3 actuators on buses.

Practise Spring (parking and emergency) brakes questionsFlashcardsOfficial chapter

How spring brakes work

  • Every air-braked vehicle must be able to stop if the service brakes fail; most combine that emergency system with the parking brake using spring brakes.
  • Spring brakes are not applied by air: they apply when air leaves the chamber and release when air pressure builds up in it.
  • A spring brake chamber has a service section (nearest the pushrod) and a piggy-backed spring section with a large coil spring; it is noticeably bigger than a service chamber.
  • About 60 psi (414 kPa) is normally needed to compress ("cage") the spring and release the brake; below that the spring brakes start to apply.
  • Many vehicles can still be driven with the spring brakes partly applied, so check that system pressure (normally 60 psi) is enough to keep them released before driving.

Hazards and caging

  • The coil spring is under very high tension; tampering, damage or corrosion can release it violently, so never service or repair a brake chamber yourself.
  • A technician can mechanically cage the spring with a caging bolt, for example to move a vehicle in an emergency or temporarily disable a failed chamber.
  • A caged chamber looks different (the bolt sticks out) and its parking/emergency brake will not apply; have the vehicle inspected and repaired immediately.

Control valves

  • The spring brake control valve is normally a push/pull valve with a yellow, four-sided (diamond) knob near the driver.
  • Usually push to supply air and release the spring brakes, pull to exhaust air and apply them; some vehicles are reversed or use a toggle, so know your vehicle.
  • Some trucks and tractors also have a tractor parking-brake valve with a round blue knob that releases the tractor's spring brakes while the trailer's stay applied.
  • When system pressure drops below about 60 psi, the control valve exhausts the remaining air, the knob pops out and the spring brakes apply suddenly, causing an uncontrolled stop.
  • If the service brakes fail, you can apply the spring brakes with the spring brake control valve.
  • Spring brakes stop and hold the vehicle only as well as the brakes are adjusted; poor adjustment weakens both service and spring braking.

DD3 brake chambers

  • Many buses and coaches use DD3 safety actuators instead of large springs; they have three air line connections instead of two and lock the brake mechanically.
  • Releasing DD3 parking/emergency brakes means operating the control valve and then pressing the brake pedal for three to five seconds.

Trailer brakes

Gladhands and colour coding, cross-connected lines, the trailer hand valve, the red trailer supply valve, the tractor protection valve and spring or service brake priority.

Practise Trailer brakes questionsFlashcardsOfficial chapter

Components

  • Trailer brake systems include air tanks and automatic spring brake application; towing vehicles need extra valves used only for the trailer.
  • A converter dolly's brake system works essentially like a trailer's.

Connecting a trailer

  • Two air connections join the trailer to the towing vehicle: the supply (emergency) line fills the trailer tanks and the service line carries service-brake pressure.
  • The connections use metal couplers called gladhands, each with a flexible seal; keep them clean and in good condition.
  • Unused couplers on the towing vehicle are protected by "dead end" or "dummy" couplers.
  • Gladhands are joined by placing the seals together at an angle and rotating them into line; once locked they take real effort to separate.
  • Couplers are usually colour-coded red for supply and blue for service, and most are shaped to fit only their match; some have no such protection.
  • Cross-connected lines make the trailer brakes work wrongly: spring brakes may not release, the towing vehicle may lose air and the service brakes will not work properly. Never drive that way.
  • Rear connectors on a trailer used for towing another trailer have manual shut-off valves to stop air loss when not in use.

Hand valve

  • Trailer service brakes apply whenever the brake pedal is pressed.
  • A trailer hand valve on the steering column or dash applies the trailer service brakes alone; if the hand valve and pedal are used together, the trailer gets the higher of the two pressures.
  • Never use the trailer hand valve for parking or emergency stops.

Trailer supply valve

  • The trailer supply valve is usually a push/pull valve with a red, eight-sided knob: push in to open and supply air to the trailer, pull out to close or when no trailer is attached.
  • Leaving it open without a trailer lets large amounts of air escape, so it closes automatically when supply-line pressure falls to between 20 and 45 psi (138–311 kPa).
  • Because air rushes out of the line, the valve usually closes well before the dash gauges fall that low.
  • If the trailer service brakes fail, you can apply the trailer spring brakes by closing the trailer supply valve.

Tractor protection valve

  • The tractor (towing vehicle) protection valve closes when the trailer supply valve closes, preventing air loss from the towing vehicle.
  • The trailer supply valve controls it; when closed, it is shut by spring force and air enters it but does not pass through.

Automatic spring brakes and priority

  • Trailer spring brakes must apply automatically when supply-line pressure drops below 60 psi (414 kPa), for example when the driver pulls the supply valve to park or when the supply line ruptures or disconnects.
  • Spring brake priority: the spring brake tank is filled first, so the trailer can roll before its service brake tank has enough air.
  • Service brake priority: the service tank fills first, ensuring service braking is available before the spring brakes release.
  • In a spring-priority trailer that loses service air, the spring brakes may stay released with no service brakes; the only way to brake the trailer is to close the trailer supply valve.
  • Ask your employer or a qualified person which priority system a trailer uses.

Speed, weight, heat and ABS

How weight and speed multiply stopping distance, brake heat and fade, retarders, why out-of-adjustment brakes go unnoticed, and what anti-lock brakes do and do not do.

Practise Speed, weight, heat and ABS questionsFlashcardsOfficial chapter

Weight and speed

  • More weight or more speed means the brakes must do more work and you must press the pedal further for higher application pressure.
  • Stopping distance increases in proportion to weight: double the weight, double the stopping distance.
  • Overloading can exceed the brake system's capacity so it may not stop the vehicle safely.
  • Stopping distance grows faster than speed: double the speed and stopping distance is four times as long.
  • Double both weight and speed and stopping distance becomes eight times as long.
  • All air brake systems have an application and release delay of up to about one-half second; allow for it in your following distance.

Heat and fade

  • Repeated braking (long or steep hills, stop-and-go traffic) or severe braking can heat brakes above normal and even damage parts.
  • Keeping a safe following distance and anticipating conditions reduces harsh braking and heat build-up.
  • Engine brakes, retarders and other auxiliary brakes help slow the vehicle and limit brake temperature.
  • Brake fade is the loss of effectiveness as brakes heat up, so you must push harder for the same force; in extreme cases, such as a long hill at excessive speed or with an overload, you may be unable to slow or stop.

Adjustment

  • Full brake capacity is rarely needed in normal driving, but it must always be available.
  • Once pushrod stroke passes the adjustment limit, brake force falls off rapidly toward zero.
  • A small loss of braking is unlikely to be noticed in normal driving; it shows up under heavy loads, high speed, long downgrades or emergency stops.
  • Ontario law requires air brake adjustment to be checked at least once a day.
  • Out-of-adjustment brakes cannot be detected except by a reliable inspection method; the vehicle has full braking only when every brake is in adjustment.

Anti-lock brakes

  • A locked, skidding wheel loses steering control and directional stability.
  • ABS senses wheel speed; an abnormal drop (impending lock) reduces brake force at that wheel, keeping steering control.
  • ABS does not shorten stopping distance, and on clean dry roads you will notice no difference.
  • ABS warning or malfunction lamps are on the dash; on trailers they are placed to be visible in the mirror.
  • If ABS malfunctions, normal braking is still available.

Compliance and safe inspection

Legal duties of drivers and operators, penalties for defective brakes, reporting defects and how to secure a vehicle safely before inspecting it.

Practise Compliance and safe inspection questionsFlashcardsOfficial chapter

The law

  • When a commercial vehicle does not meet the Highway Traffic Act and regulations, the driver, operator and owner must keep it off every road and highway.
  • Driving a non-compliant vehicle is an offence; penalties range from fines to detainment or impoundment of the vehicle.
  • Driving with defects or failing to do required inspections can lead to charges against the driver and/or the operator.
  • Drivers are required by law to report air brake defects to the vehicle operator.
  • It is illegal to operate or drive a vehicle with a defective air brake system.

Safe inspection practice

  • Park on a level surface, because some checks are done with the parking brakes released.
  • Park away from traffic and other hazards.
  • Turn off the engine for inspections around moving engine parts.
  • Chock the wheels whenever a check requires you to leave the seat with the parking brakes released.
  • Keep out of the path of air exhausting from brake components.
  • Never leave the driver's seat or get under the vehicle unless the spring brakes are applied or the wheels are securely blocked.
  • Wear proper safety equipment such as safety glasses, steel-toe shoes and a bump cap when inspecting.

Context

  • Air brakes out of adjustment are the most common reason a commercial vehicle is taken out of service.
  • A full air brake pre-trip inspection, as set out in the Air Brake Handbook, should be done before the day's trip.

Inspecting brake components

Lining contact, cracks, contamination and thickness, chamber leaks and matching sizes on the steering axle, slack adjuster length, drums, air lines, tanks and compressor belts.

Practise Inspecting brake components questionsFlashcardsOfficial chapter

General

  • The driver's inspection mainly means looking at the visible components for defects or anything abnormal.
  • Know the normal appearance of each part and the signs of present or developing defects.

Foundation brakes

  • When the brakes are applied the lining must contact the drum; when released it must be clear. Lining that does not touch the drum when applied means a malfunctioning brake.
  • Lining that is noticeably cracked, loose or missing is defective.
  • Lining contaminated with grease or oil (often leaking from the wheel) is defective and causes abnormal braking.
  • Lining worn below the prescribed minimum thickness is defective.
  • Damaged, missing or malfunctioning foundation components are defects; the vehicle may not be driven with any of them.

Brake chambers and slack adjusters

  • Chamber size is the diaphragm area in square inches; brakes at each end of an axle should have the same size for balanced braking, which matters most on the steering axle.
  • Chambers from different makers can look different even at the same size.
  • Check chambers for leaks with air applied (spring brakes released, service brakes applied); leaks are usually heard.
  • Vent holes made by the manufacturer are normal; holes or cracks from impact or damage make the chamber defective.
  • Slack adjusters are levers that multiply chamber force; effective length is the distance from the camshaft centre to the clevis pin.
  • Using the wrong pushrod hole changes effective length; slack adjusters on each side of a steering axle must have the same effective length.
  • Defects: audible leaks, cracks or non-manufactured holes, mismatched chamber size or mismatched slack adjuster length on a steering axle.

Drums, lines, tanks, compressor

  • Drums and rotors may be hidden by wheels or shields; cracked or broken drums or rotors are defects and often change how the brakes behave.
  • Air lines have an inner airtight layer, reinforcing layers and an outer cover; damage reaching the reinforcing or inner layer makes the line defective, even before it leaks.
  • Wear, cuts, abrasion and heat damage are typical line damage; moving a hose back and forth helps find a leak.
  • Only fittings designed and approved for air brakes may be used; improper fittings or repairs are prohibited.
  • Air tanks must be firmly attached; check by looking and by trying to move them, along with their brackets.
  • Inspect the compressor with the engine stopped: it and its brackets must be secure; a drive belt should give slightly under firm hand pressure, and a loose, cut or frayed belt is defective.

Brake adjustment and pushrod stroke

Daily stroke checks, identifying chamber size and long-stroke chambers, the two measuring methods at 90 to 100 psi, the adjustment limits chart and automatic slack adjusters.

Practise Brake adjustment and pushrod stroke questionsFlashcardsOfficial chapter

Why and how often

  • As brakes wear, pushrod stroke increases; wear rates vary with the vehicle and conditions.
  • Pushrod stroke must be inspected at least daily; when it exceeds the adjustment limit the brake is out of adjustment.
  • Measuring the applied pushrod stroke is the most reliable way to check adjustment.

Identifying the chamber

  • Adjustment limits depend on chamber size and type, so you must identify the chamber.
  • Size can be found by measuring the clamp diameter (special tool) or reading the size marking, which may need cleaning first; the easiest source is the employer or the owner's manual.
  • Size 30 is the most common; sizes 16, 20, 24 and 36 are also used.
  • Long-stroke chambers have square air ports (standard chambers have round ports), a trapezoidal tag under the clamp bolt showing maximum stroke (not the adjustment limit), and markings saying to use only long-stroke diaphragms.
  • Square ports are the most visible and permanent sign of a long-stroke chamber.
  • Limits for standard and long-stroke chambers of the same size can differ by 19 mm or more.

Measuring applied stroke

  • Chock the wheels, make sure pressure is above 90 psi (621 kPa) and release the spring brakes.
  • Method 1: put a narrow, precise chalk or marker line on the pushrod at the chamber or a fixed reference point.
  • Method 2: measure the distance from a point on the pushrod to a fixed point at the chamber (measurement 1).
  • Bring both primary and secondary gauges to 90–100 psi (621–690 kPa), shut off the engine and hold the pedal fully applied.
  • Method 1: measure from the chamber or reference point to the mark. Method 2: measure again (measurement 2) and subtract measurement 1.
  • Identify the chamber size and type, look up its adjustment limit and mark any brake that exceeds it as defective.
  • Demonstrating an applied-stroke measurement is part of the MTO air brake practical test.

Clamp-type chambers

  • Type 30 standard: 2 in. (51 mm). Type 30 long-stroke with square ports: 2-1/2 in. (64 mm).
  • Types 16, 20 and 24 standard: 1-3/4 in. (45 mm); their long-stroke "L" versions: 2 in. (51 mm).
  • Type 24 long-stroke with square ports: 2-1/2 in. (64 mm).
  • Type 36 standard: 2-1/4 in. (57 mm). Type 30 DD3 (bus/coach): 2-1/4 in. (57 mm).
  • Type 12 and type 9: 1-3/8 in. (35 mm). Type 6: 1-1/4 in. (32 mm).

Indicators and slack adjusters

  • Many pushrods have an indicator that becomes visible when stroke passes the limit; indicators must be correctly installed and drivers trained to read them.
  • Automatic slack adjusters avoid routine manual readjustment, but adjustment must still be inspected.
  • An automatic slack adjuster that keeps needing readjustment is defective and must be repaired by a certified technician; never adjust it yourself.
  • Only certified technicians, or drivers holding an Ontario air brake adjustment certificate, may readjust manual slack adjusters; that certificate does not cover automatic adjusters.
  • Ontario law prohibits operating a vehicle with a brake out of adjustment.

Air brake system tests

Pass and fail limits for the low-air warning, build-up time, governor settings, air-loss rates, tractor protection valve, trailer and spring brake tests and draining tanks.

Practise Air brake system tests questionsFlashcardsOfficial chapter

Before testing

  • Park on level ground, apply the spring brakes and chock the wheels before starting.

Low air-pressure warning

  • Start above 90 psi (621 kPa); the engine may run or be off but the ignition must be on.
  • Press and release the brake pedal repeatedly to lower pressure and note the gauge reading when the warning activates.
  • Pass: the warning activates at or above 55 psi (380 kPa) on both primary and secondary gauges. Fail: it does not activate, or activates below 55 psi on either gauge.
  • The pressure at which the warning switches off on the way up need not match where it came on.
  • If pressure is too low at the start, the warning comes on as soon as the key is turned on.

Build-up time

  • Close the trailer supply valve if a trailer is attached and lower pressure below 80 psi (552 kPa).
  • With the engine at 600 to 900 rpm, time the rise from 85 psi to 100 psi (587–690 kPa).
  • Pass: two minutes or less. Fail: more than two minutes.

Governor settings

  • Run the engine until pressure stops climbing: that is cut-out (an air dryer purge also signals it).
  • Pump the brakes slowly and note where pressure starts to climb again: that is cut-in, often heard as a change in engine sound.
  • Fail: cut-out above 145 psi (1000 kPa) or cut-in below 80 psi (552 kPa); changes from the manufacturer's range should be reported.
  • Older vehicles may have lower governor settings; operating pressures have risen over the past 20 years.

Air-loss rate

  • Release the spring brakes, establish normal pressure, shut off the engine and hold the pedal fully applied; watch the gauges for one minute after the first drop settles.
  • Maximum loss per minute: straight truck, tractor or bus 3 psi (21 kPa); tractor and trailer 4 psi (28 kPa); tractor with two or more trailers 6 psi (41 kPa).

Tractor protection valve

  • With normal pressure, close (pull out) the trailer supply valve, disconnect the trailer service-line gladhand where you can see it and apply the service brakes.
  • Pass: no air comes out of the service line. Fail: air exhausts from it.
  • If the vehicle may lack an anti-compounding valve, secure it and release the spring brakes before applying the service brakes.

Trailer spring brakes

  • With the trailer fully charged (supply valve pushed in), pull the supply valve out; air should be heard exhausting as the trailer spring brakes apply.
  • Disconnecting the supply line also works but is not recommended while it is under pressure.
  • If unsure, gently apply engine power to confirm the trailer will not move; if the brakes do not apply, they are defective.

Spring brake holding test

  • Apply the spring brakes on the unit being tested, remove the chocks and gently apply engine power in a low gear.
  • The vehicle may rock, but it must not move significantly; preferably test the towing vehicle's spring brakes.

Drain valves

  • Drain the supply tank first until only clean air comes out, then drain the other tanks and confirm every drain valve works.
  • Some moisture from the supply tank is normal; a significant amount from the other tanks is not and must be reported.
  • Any visible oil in the supply tank should be reported or repaired; oil in any other tank risks contaminating the system and must be reported.
  • A sudden increase in moisture or oil from any tank, or a malfunctioning drain valve, must be repaired.

Getting and renewing the Z endorsement

Who needs a Z endorsement, course and DriveTest routes, the referral envelope, practical test versions and equipment, and the online renewal module since 2023.

Practise Getting and renewing the Z endorsement questionsFlashcardsOfficial chapter

Who needs it

  • In Ontario you need a Z endorsement on your licence to drive a vehicle with air brakes or air-over-hydraulic brakes.
  • You can earn it by taking an air brake endorsement course, or by taking the tests at a DriveTest centre.
  • The Official Air Brake Handbook is the study guide for the knowledge test; it is free online or can be bought in print.

Courses

  • Courses are offered by vehicle fleet owners, community colleges and safety organizations.
  • Class A holders upgrading to Z can use any of those three; holders of B, C, D, E, F or G must take the course with a fleet owner.
  • After the course you receive a referral envelope, which must be taken to a DriveTest centre within 6 months.

Tests

  • The knowledge test is taken at a DriveTest centre and requires a fee; after passing it you book the practical test.
  • There are two practical test versions: Version 1 for vehicles with a tractor-trailer air brake system, Version 2 for other air-braked vehicles.
  • Bring wheel chocks, a stopwatch or watch with a second hand, knowledge of every brake chamber's size and type, something to hold the pedal applied, a way to mark the pushrod, a stroke-measuring device and protective eyewear (the last three are not needed for motor coaches); a brake adjustment chart is optional.
  • On the practical test, tell the examiner what you are testing at each step.
  • Cancel a test at least 48 hours ahead to avoid a cancellation fee.

Renewal

  • Since September 1, 2023, renewing a licence with a Z endorsement requires completing an online air brake learning module instead of the air brake knowledge test.
  • Bring the certificate of completion (digital or printed) and your licence to a DriveTest centre or your Driver Certification Program organization.
  • Commercial-class holders also complete the vision and commercial knowledge tests in person when renewing.
  • From age 80, the learning module and the practical test are required every year; under 80, renewal is usually every five years.
  • If you cannot do the module online, you can complete it in person at a DriveTest centre.

Written in our own words from: The Official Air Brake Handbook (MTO)

FAQ

Ontario Air Brake (Z) study guide: common questions

What is the best way to use this Ontario Air Brake (Z) study guide?

Read one topic, then answer that topic's practice questions while the rules are fresh. Note the questions you miss, re-read those notes, and finish with a full practice test across all 12 topics.

Is this the official Ontario Air Brake (Z) handbook?

No. It is our own summary of the The Official Air Brake Handbook (MTO). Use it to review, and use the official handbook when you need the exact wording of a rule.

Can I print the study guide?

Yes, with your browser's print command. For practice questions on paper with an answer key, use our printable questions and answers page instead.

Keep practising

Practice by topic