How to get a Z endorsement
A Z endorsement is needed to drive any vehicle with air brakes or air-over-hydraulic brakes. The steps are:
- Take an air brake endorsement course from a vehicle fleet owner, community college or safety organization. Holders of Class B, C, D, E, F or G licences must use a fleet owner. Class A holders may use any of the three.
- Take the referral envelope you receive to a DriveTest centre within 6 months.
- Pass the air brake knowledge test. Study the Official Air Brake Handbook.
- Book and pass the practical test.
There are two versions of the practical test. Version 1 is for vehicles with a tractor-trailer air brake system. Version 2 is for vehicles without one. You must show the applied method of measuring push rod stroke.
- Bring wheel chocks or blocks.
- Bring a stopwatch or a watch with a second hand.
- Know your brake chamber sizes and types.
- Bring a way to hold the brake pedal down.
- Bring a way to mark the push rod and a device to measure push rod stroke, plus protective eyewear (not needed for motor coaches).
Since September 1, 2023, Class A or D drivers with a Z endorsement complete an online Air Brakes Refresher Training module before renewing, instead of a knowledge test. At 80 and older, you complete the module and a practical test every year.
Parts of an air brake system
Air flows from the compressor to the tanks, then to the brakes when you press the pedal.
- Air compressor, driven by the engine.
- Governor, which controls when the compressor cuts in and cuts out.
- Air tanks (reservoirs).
- Drain valve at the bottom of each tank.
- Brake pedal (foot valve), which sends air to the brakes.
- Brake chamber, which turns air pressure into force on the push rod.
- Slack adjuster, a lever that links the push rod to the camshaft.
- Brake drum, where the shoes press to slow the wheel.
| Part | What it does |
|---|---|
| Air dryer | Removes moisture before air reaches the supply tank. |
| Alcohol evaporator | Adds alcohol vapour to reduce freezing in the system. |
| Supply (wet) tank | Gets air first and collects most of the water and oil. |
| One-way check valve | Stops air flowing back out of a tank. |
| Safety valve | Opens to let out air if pressure gets too high. |
| Tractor protection valve | Keeps the tractor's air if there is no trailer or the trailer lines fail. |
| Trailer supply valve | A red, eight-sided push-pull knob that feeds air to the trailer. |
| Gladhands | Couplers for the trailer air lines: red for supply, blue for service. |
| Wig wag | A warning arm that drops into view when pressure is low. |
Three kinds of brakes
- Service brakes do normal stopping. You apply them with the pedal.
- Spring brakes are parking and emergency brakes. A strong spring applies them, and air pressure holds them off. If air is lost, the springs apply the brakes.
- Foundation brakes are the parts at each wheel, such as drums or rotors, shoes or pads, and camshafts.
A dual air system splits air from the supply tank into a primary and a secondary circuit. If one fails, the other should still stop the vehicle. The gauges show both circuits. Buses and coaches may use DD3 chambers, which have three air connections and no large spring.
A technician can cage a spring brake by compressing the spring with a caging bolt, for example to move a vehicle in an emergency. A caged spring brake will not apply. The spring is under very high tension, so never try to take a chamber apart.
Pressures you must know
| Item | Ontario handbook figure |
|---|---|
| Normal operating range | 690 to 828 kPa (100 to 120 psi) |
| Lowest allowed cut-in pressure | 552 kPa (80 psi) |
| Highest allowed cut-out pressure | 1000 kPa (145 psi) |
| Gap between cut-out and cut-in | 138 to 173 kPa (20 to 25 psi) |
| Safety valve opens | About 1035 kPa (150 psi) |
| Low air warning must come on | Not below 380 kPa (55 psi); most come on at 414 kPa (60 psi) or higher |
| Spring brakes fully released | About 414 kPa (60 psi) |
| Trailer supply valve closes by itself | 138 to 311 kPa (20 to 45 psi) |
If the low air warning comes on while you are driving, you are losing braking power. Stop safely and find the cause.
The pre-trip air brake inspection
The inspection has a mechanical part and a functional part. For the mechanical part, park on level ground away from traffic, shut off the engine, apply the spring brakes and chock the wheels. Then check:
- Brake linings, drums or rotors for wear, cracks or missing parts.
- Brake chambers for air leaks, cracks or mismatched sizes on an axle.
- Air lines for leaks, damage or wear.
- Air tanks for secure mounting.
- The compressor's drive belt, pulley and mounting.
Functional tests
- With the spring brakes applied and wheels chocked, build pressure to at least 621 kPa (90 psi). Turn the ignition on and fan the brake pedal until the low air warning comes on. It is defective if it does not come on or comes on below 380 kPa (55 psi).
- Test build-up time: with pressure first lowered below 552 kPa (80 psi), pressure must rise from 587 to 690 kPa (85 to 100 psi) within 2 minutes at 600 to 900 rpm.
- Check the governor cut-in and cut-out pressures.
- Test the air-loss rate over one minute.
- Test the tractor protection valve: no air should exhaust from the trailer service line when you press the pedal.
- Close the trailer supply valve: the trailer spring brakes must apply.
- Test the spring brakes by gently applying engine power: they must hold the vehicle.
- Drain the tanks, starting with the supply (wet) tank, and check each drain valve.
| Vehicle | Most air lost in one minute |
|---|---|
| Straight truck, tractor or bus | 21 kPa (3 psi) |
| Tractor and trailer | 28 kPa (4 psi) |
| Tractor and two or more trailers | 41 kPa (6 psi) |
It is illegal to drive a defective vehicle, and you must report defects.
Brake adjustment and push rod stroke
Check brake adjustment at least daily. Release the spring brakes, keep pressure at 621 to 690 kPa (90 to 100 psi), fully apply the service brakes and measure the applied push rod stroke at each wheel. A brake is out of adjustment, and defective, if the stroke is more than the limit for that chamber.
| Chamber | Adjustment limit |
|---|---|
| Type 24 (standard) | 45 mm (1-3/4 in) |
| Type 24 long-stroke (L) | 51 mm (2 in) |
| Type 30 (standard, most common) | 51 mm (2 in) |
| Type 30 long-stroke (LS) | 64 mm (2-1/2 in) |
| Type 30 DD3 (bus or coach) | 57 mm (2-1/4 in) |
| Type 36 | 57 mm (2-1/4 in) |
An L stamped on the chamber cover means a long-stroke design, which has a longer limit. Only certified technicians may adjust manual slack adjusters. If an automatic slack adjuster keeps needing adjustment, it has a defect.
Using air brakes safely
There is a delay of up to about half a second between pressing the pedal and the brakes applying. Weight and speed change stopping distance a lot:
- Double the weight: about double the stopping distance.
- Double the speed: about four times the stopping distance.
- Double both: about eight times the stopping distance.
Brake fade happens when brakes overheat and lose power, so you must press harder. Long downhill runs, overloading and too much speed can cause severe fade. Engine brakes and retarders help keep the service brakes cool.
Key numbers at a glance
Many questions ask for a number. This table puts the main ones from the Official Air Brake Handbook in one place.
| What | Number |
|---|---|
| Normal operating range | 690 to 828 kPa (100 to 120 psi) |
| Cut-in not below / cut-out not above | 552 kPa (80 psi) / 1000 kPa (145 psi) |
| Low air warning not below | 380 kPa (55 psi) |
| Spring brakes fully released at about | 414 kPa (60 psi) |
| Trailer supply valve closes | 138 to 311 kPa (20 to 45 psi) |
| Build-up test | 587 to 690 kPa (85 to 100 psi) in 2 minutes or less |
| Air-loss limits per minute | 21 kPa (3 psi) single; 28 kPa (4 psi) with trailer; 41 kPa (6 psi) with two or more trailers |
| Brake adjustment check pressure | 621 to 690 kPa (90 to 100 psi) |
| Brake lag | Up to about half a second |
| Referral envelope to DriveTest | Within 6 months |
Common mistakes on the test
- Mixing up cut-in and cut-out. The compressor cuts out (stops pumping) at the high pressure and cuts in (starts again) at the lower pressure.
- Forgetting the order of the drain step. Drain the supply (wet) tank first, because it collects most of the water and oil.
- Confusing the two red-and-blue ideas. The trailer supply valve knob is red and eight-sided. The red gladhand is the supply line; the blue one is the service line.
- Measuring released stroke instead of applied stroke. The handbook uses the applied method: the brakes are fully applied when you measure.
- Thinking any driver may adjust brakes. Only certified technicians may adjust manual slack adjusters, and a frequently re-adjusted automatic adjuster has a defect.
- Forgetting what the spring brakes do. They are applied by springs and released by air, so they come on when air is lost.