BC Class 1–4 study guide: key rules on all 24 topics (Part 2)

Free BC Class 1–4 study guide: 1032 key points from the Driving Commercial Vehicles in plain words, organised by topic, each topic linked to its practice questions.

By the Canada Exam Prep Editorial Team · Updated October 17, 2026

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Hours of service

On-duty and off-duty time, daily and shift limits, cycles and resets, deferral, sleeper berths, personal use, ELDs and records of duty status, the 160 km exemption and other jurisdictions.

Practise Hours of service questions Flashcards Official chapter

National Safety Code (p. 133)

The National Safety Code (NSC) sets minimum safety standards for commercial vehicles, drivers and carriers in Canada; carriers must ensure drivers and vehicles meet them.
NSC covers commercial vehicles licensed over 5,000 kg GVW, vehicles under the Passenger Transportation Act (taxis, buses, limousines) and commercial vehicles seating 10 or more passengers plus the driver.
In B.C., NSC hours of service are in Division 37 of the Motor Vehicle Act Regulations.
Hours of service rules exist because a fatigued driver is more likely to crash.

On-duty and off-duty time (p. 134)

On duty includes driving, and inspecting, servicing, repairing, conditioning or starting a commercial vehicle.
On duty also includes being a co-driver not resting in the sleeper berth, loading or unloading, checking the load, and waiting at customs, a scale or for a peace officer.
Waiting along the route because of a crash or other unexpected event is on-duty time.
Riding as a passenger to where you will start driving is on duty if the carrier asked you to and you did not have eight consecutive hours off immediately before.
Time on a ferry is not on-duty time unless you are working (for example, a bus driver selling tickets).
Off-duty time is any time not on duty and includes time in a sleeper berth.
At least 10 hours off duty every day.
Off-duty time beyond the eight consecutive hours can be taken in blocks of 30 minutes or more.
Each day must include at least two hours of off-duty time that is not part of the eight-consecutive-hour period.
Every driver must take 24 consecutive hours off duty in every 14 days.

Day, work shift and cycles (p. 134–136)

A "day" is a 24-hour period starting at the hour the carrier sets.
Daily limits: at least 10 hours off duty, no more than 13 hours driving, no driving after 14 hours on duty.
You can put in 14 hours on duty without driving at all.
A work shift is the time between two off-duty periods of at least eight consecutive hours; no driving after 16 hours have elapsed since the shift started.
Any off-duty period of eight consecutive hours or more resets the work shift.
Cycle 1: no driving after 70 on-duty hours in seven days.
Cycle 2: no driving after 120 on-duty hours in 14 days, and 24 consecutive hours off must be taken before reaching 70 on-duty hours.
Reset Cycle 1 with 36 consecutive hours off; reset Cycle 2 with 72 consecutive hours off.
The cycle start time stays the same; you must reset the cycle to change it.

Deferring off-duty time (p. 136)

You may defer up to two hours of the daily 10 off-duty hours to the next day.
The deferred hours must not be part of the eight consecutive off-duty hours and must be added to the next day's eight consecutive hours.
Mark the deferral as "Day 1" and "Day 2" in the record of duty status.
Under the 160 km local exemption, off-duty time cannot be deferred.

Sleeper berth (p. 136–137)

The same driving and on-duty limits apply to sleeper berth drivers.
A bus back seat or a reclining seat is not a sleeper berth.
A single driver may split off-duty sleeper time into two periods if neither is under two hours and the total off duty is at least 10 hours.
Team drivers may split sleeper time into two periods if neither is under four hours, the two total at least eight hours and total off duty is at least 10 hours.

Personal use exemption (p. 138)

Personal driving of a commercial vehicle is not on-duty time if it is not used for the carrier's business, is unloaded, tows no trailer, travels at most 75 km a day, odometer readings are logged, and you are not under an out-of-service declaration.

Electronic logging devices and RODS (p. 138–141)

Electronic logging devices (ELDs) have been required since August 1, 2023, unless exempt (for example, local driving).
An ELD automatically records driving time, must be certified by an accredited body and must be mounted in a fixed position visible from the normal driving position.
A driver must not use more than one ELD for the same period and must certify the day's record right after the last entry.
The carrier must keep an ELD information packet in each vehicle: user's manual, data-transfer instructions, malfunction instructions and enough paper records of duty status for at least 15 days.
If an ELD malfunctions, tell the carrier as soon as the vehicle is parked; the carrier must repair or replace it within 14 days (or by trip end if the trip is longer); use an alternate RODS meanwhile.
A paper RODS includes date, start time if not midnight, printed name and signature, co-driver, start and end odometer, distance driven, plate or unit number, cycle, carriers and their addresses, and hours in each duty status.
The duty-status totals on a RODS must add up to 24 hours.
Record the place (municipality or highway location and jurisdiction) of every change in duty status.
Carry your RODS up to the last change in duty status plus copies for the present day and the previous 14 days (24 days under oilwell service hours) and supporting records.
Submit RODS and supporting records to your carrier within 20 days.
Peace officers (police, commercial transport inspectors, motor vehicle inspectors) may demand your RODS and supporting records such as bills of lading, shipping documents, fuel and accommodation receipts.
Driving after reaching the cycle's maximum on-duty hours can get you ordered out of service; only the driver, not the vehicle, is out of service.

160 km radius exemption (p. 142)

No RODS or ELD is needed if you stay within 160 km of the home terminal, take 10 hours off duty in the day and return to the terminal each day to start at least 10 consecutive hours off duty.
The carrier must then record start and release times, total on-duty hours and the cycle, and keep them at least 6 months.

Other jurisdictions (p. 142–143)

North of the 60th parallel (Yukon, Northwest Territories, Nunavut): up to 15 hours driving, no driving after 18 hours on duty, eight consecutive hours off after that.
North of 60: Cycle 1 is 80 on-duty hours in seven days; Cycle 2 is 120 hours in 14 days with 24 consecutive hours off before reaching 80 hours.
In the U.S.: up to 11 hours driving after 10 hours off; no driving beyond the 14th hour after coming on duty; 60 hours in seven days or 70 in eight days; restart after at least 34 consecutive hours off; drug and alcohol testing program.
A B.C. driver may not drive a commercial vehicle in the U.S. with a history of epilepsy, insulin-controlled diabetes, or without meeting U.S. hearing standards.

Air brake components

Why air brakes, brake chambers and slack adjusters, s-cam brakes, compressor, governor, reservoirs, foot valve, air dryers and ABS.

Practise Air brake components questions Flashcards Official chapter

Why air brakes? (p. 145–146)

Air brakes apply much more force than hydraulic brakes, which heavy commercial loads need.
Air brakes tolerate small leaks because the compressor makes more air as needed; a small leak in a hydraulic system could mean brake failure.
Compressing air into a smaller space creates pressure that can be turned into mechanical force.
10 pounds of force on one square inch is 10 p.s.i., about 68.9 kPa.

Basic components and force multipliers (p. 146–149)

The simplest air brake system has a compressor with a governor, air lines, a reservoir, a foot valve (brake pedal) and foundation brakes.
Foundation brakes include brake chambers, slack adjusters, brake linings and drums or rotors.
The slack adjuster both adjusts for lining wear and acts as a lever that multiplies force.
The brake chamber turns air pressure into mechanical force through the pushrod and slack adjuster.
A brake chamber has a flexible diaphragm (reinforced fabric with a rubber coating) clamped between two steel housings, a pushrod and plate assembly and a return spring.
Pushrod force depends on air pressure (p.s.i.) times the effective diaphragm area (square inches).
A Type 30 chamber has 30 square inches of effective area and gives about 3,000 pounds of pushrod force at 100 p.s.i. (690 kPa).
Chambers range from Type 9 (9 square inches) to Type 36 (36 square inches) so each axle gets the right braking force.
The Type 30 clamp chamber is the most common size on truck drive axles and trailer axles.
Long stroke chambers have a longer pushrod stroke and are identified by square inlet ports and/or a trapezoid-shaped tag on a clamp bolt.
Normal stops usually use less than 20 p.s.i. (138 kPa) of application pressure even though system pressure is 100 p.s.i. or more.
With air applied, the slack adjuster sits at about 90 degrees to the pushrod.

Foundation brakes: s-cam type (p. 149–150)

The foundation brake is the brake assembly at each wheel, including the brake chamber; the s-cam drum brake is the most popular type.
Air pushes the pushrod forward, the slack adjuster rotates the camshaft and its s-shaped head spreads the linings against the drum.
Brake shoe return springs pull the linings away from the drum when the air is released.
The linings are mounted on the axle housing; the drum is mounted on the wheel and turns with it.

Compressor (p. 150–152)

The compressor takes in outside air, compresses it and pumps it to the supply reservoir.
It is driven by the engine, by gears or by a belt, and runs whenever the engine runs.
All trucks use piston-type compressors with one, two or four cylinders.
At 120 p.s.i. (827 kPa), air leaving the compressor is over 204 °C (400 °F).
Most heavy-truck compressors are cooled by engine coolant; some on lighter units are air-cooled.
The compressor is usually lubricated by engine oil, sometimes by its own supply; oil also helps cool it.
The compressor shares the engine's air filter, which must be checked so it is not clogged.
Intake stroke: piston moves down, inlet valve open, air drawn in; compression stroke: inlet valve closed, discharge valve opens near the top and air goes to the reservoir.
Check a compressor belt by pressing midway between pulleys; if it deflects more than double the belt's width, it needs adjusting.

Governor (p. 152)

A compressor can make over 500 p.s.i. (3,448 kPa); most systems run at a maximum of about 125 p.s.i. (862 kPa).
The governor "unloads" the compressor (stops it pumping) at about 125 p.s.i. by making the unloader piston hold the inlet valve open.
Maximum (cut-out) pressure may range from 105 to 135 p.s.i. (724 to 931 kPa); the spread between cut-in and cut-out should be about 20 p.s.i. (138 kPa).
Example: cut-out at 125 p.s.i. means cut-in at about 105 p.s.i.
Safety standards require the governor to restart the compressor if pressure falls below 80 p.s.i. (552 kPa); in any case it must cut in by 80 to 85 p.s.i.
The compressor must build reservoir pressure from 50 to 90 p.s.i. within three minutes at fast idle (1,000–1,200 r.p.m.).

Reservoirs (p. 153)

Steel reservoirs store compressed air.
A safety valve (pop-off valve) on the first reservoir is a spring-loaded ball that vents excess air, normally at about 150 p.s.i. (1,034 kPa), if the governor fails to unload the compressor.
If the safety valve has to vent, the governor or compressor needs repair by a qualified mechanic.
Compressed air carries water vapour, oil and carbon that form a grey sludge; the supply reservoir is therefore called the wet tank.
Water causes valve trouble and can freeze in winter, jamming valves or brake chambers.
Every reservoir has drain valves (drain cocks); most makers recommend draining daily and letting the air drain completely.
Stay out of the path of escaping air when draining; it can injure eyes and ears.
Some reservoirs have more than one compartment and more than one drain cock.

Foot valve and how air brakes work (p. 153–155)

The foot valve (treadle) is a foot-controlled pressure regulator; pressing it farther, not harder, gives more braking.
Holding the treadle still holds the application pressure constant, and the valve tops up small leaks downstream automatically.
Releasing the treadle exhausts application air through the foot valve's exhaust port.
A brake application can never exceed reservoir pressure; with 80 p.s.i. in the reservoirs, the maximum application is 80 p.s.i.
On release, chamber return springs pull the pushrods back and shoe return springs pull the linings off the drums.

Other types of foundation brakes (p. 177–180)

Besides s-cam brakes, air-braked vehicles may have wedge brakes, air disc brakes or air-over-hydraulic brakes.
Wedge brakes use one or two small chambers with wedge-shaped pushrods that push between rollers to spread the linings; they are usually only on steering axles.
Most wedge brakes have internal automatic adjusters; if either lining moves more than 1/16 inch, or both together more than 1/8 inch, the adjusters have failed.
Drivers cannot easily check wedge or air disc brake adjustment; only a qualified mechanic should adjust or repair them.
Air disc brakes squeeze two pads against a rotor on the hub, like a large C-clamp; most self-adjust and have the same chamber stroke limits as automatic slack adjusters.
Air-over-hydraulic brakes are common on middleweight trucks and buses: air actuates hydraulic pressure intensifiers, and hydraulic pressure applies the foundation brakes.
Air-over-hydraulic systems have a compressor, governor, tanks, foot valve and two intensifiers, run at about 125 p.s.i., and may have spring parking brakes that force a wedge between the shoes.
Diesel engines do not provide usable vacuum for brake boosters, which is why a partial air system is used on these vehicles.
An air brake endorsement is required for most air-over-hydraulic vehicles; the only exception is a system without an air treadle.

Air dryers, alcohol systems and automatic drains (p. 180–182)

An air dryer sits in the discharge line between the compressor and the first reservoir and removes water vapour, oil mist and carbon.
When the reservoir reaches full pressure, the dryer's purge port opens and blows out the collected contaminants; clean air back-flushes the filters.
Some air dryers have an electric heater to prevent freezing; with a dryer, the safety valve is often mounted on the dryer.
Even with an air dryer, drain the reservoirs regularly; more than a few drops of water may mean the dryer or compressor needs service.
Integrated dryer systems combine filter, dryer and governor with a purge reservoir and no wet tank; one service reservoir fills first, the other starts at about 100 p.s.i., and maximum may be up to 135 p.s.i.
Alcohol evaporators (on the compressor intake side) and alcohol injectors (in the discharge line, using a venturi) add alcohol vapour as anti-freeze for moisture.
Keep the alcohol reservoir topped up with methyl hydrate made for air brake systems through winter, starting before the first freeze; reservoirs must still be drained.
Automatic drain ("spitter") valves expel contaminants each time reservoir pressure drops 2 or 3 p.s.i., or each time the compressor cycles; open the manual drains periodically anyway.

Front wheel limiting, emergency release, pressure protection (p. 182–184)

An automatic front wheel limiting (ratio) valve has no dash control; below about 5 to 15 p.s.i. no air reaches the steering axle brakes.
Below 40 p.s.i. application the automatic limiting valve gives the steering axle about 50 per cent of drive axle pressure; at emergency pressures of 60 to 70 p.s.i. both axles get equal pressure.
Manual front wheel limiting valves (no longer installed on new vehicles) have a dash control: "dry" gives equal pressure, "slippery" gives the steering axle 50 per cent.
The slippery-road position may be used only when weather makes it essential for safety; front wheel skids are less dangerous than drive axle lockup.
A spring parking brake emergency release system ("California" system) has a separate tank and a hold-down ("dead man") dash valve to release spring brakes to move a disabled vehicle; it is still found on some transit buses, school buses and fire trucks.
Pressure-protection valves cut air to non-essential accessories (air seats, horns, wipers, suspension, fifth wheel sliders, air shifts) if a failure drops service pressure below a preset point of 60 to 90 p.s.i.
Application pressure gauges show the actual pressure delivered to the service brakes, sometimes separately for tractor and trailer.

Anti-lock braking systems (p. 184–186)

ABS has three parts: wheel speed sensing, decision-making by an electronic control unit (ECU), and brake release or modulation.
Magnetic pickups near toothed rings on the hubs generate a pulsing current; a sudden drop tells the ECU a wheel is locking.
Solenoid valves called modulators release and reapply air at the affected wheel, up to about five times per second.
On a very slippery surface, apply and hold firm, continuous pedal pressure and let ABS work; noise and vibration are normal and you keep steering control.
The ABS warning lamp comes on at ignition for a self-check; if it stays on or lights while driving, ABS has failed but normal braking still works and the vehicle may be driven to a service depot.
Trailer ABS has a warning light on the left side of the trailer (front or rear) visible in the tractor mirror; some tractors also have a trailer ABS dash light.
The trailer ABS ECU may be powered from the stop lamp circuit or a dedicated circuit in the electrical connector.

Dual air brake systems

The dual foot valve, primary and secondary circuits, one-way check valves, the low-air warning, quick release and relay valves, and what happens when one circuit fails.

Practise Dual air brake systems questions Flashcards Official chapter

Dual air brake systems (p. 155–156)

Dual air brake systems have been used since the mid-1970s; cars have had dual brake systems since 1968.
The dual foot valve is two control valves worked by one pedal, splitting the system into two independent sections with their own supply, delivery and exhaust ports.
The primary section is nearest the pedal and in many systems works the drive (rear) axle brakes; the secondary usually works the steering axle brakes.
Most dual systems have three reservoirs: the supply reservoir (wet tank) and two service reservoirs called primary and secondary.
If either section fails completely, the driver can still make a controlled stop with the foot valve, with less maximum braking.
Some dual systems connect the low-air warning to the supply reservoir; others connect one to each service reservoir.

Components of a dual system (p. 156–157)

Most contaminants settle in the supply reservoir, so the primary and secondary reservoirs give cleaner air to every component except the governor.
One-way check valves let air flow from the supply reservoir into the primary and secondary reservoirs but not back.
The check valves keep primary and secondary air from being lost if the compressor, its discharge line or the supply reservoir fails.
Every air-brake vehicle has at least one dash gauge showing service reservoir pressure; many use one gauge with two needles (primary and secondary).
Many vehicles also have an application pressure gauge showing how much air the foot valve is applying.

Low-air warning device (p. 157–158)

Every air-brake vehicle must have a low-air warning that comes on before pressure drops below 60 p.s.i. (414 kPa); many come on above 60.
Low pressure can come from a leak or from braking repeatedly faster than the compressor can refill.
Most are a dash light, often with a buzzer; older vehicles may have a wig-wag that drops into view near the top of the windshield.
Some wig-wags retract automatically above 60 p.s.i.; others must be pushed back up by hand.
When the warning comes on, stop and find the cause; the roughly 60 p.s.i. left is enough to stop if you act promptly; do not continue until the system is safe.

Quick release and relay valves (p. 158–160)

A quick release valve lets brakes release quickly by exhausting chamber air near the chambers rather than back at the foot valve.
On release, the bigger air burst comes from the quick release valve; only the line between it and the foot valve vents at the foot valve.
Quick release valves can be on front brakes, rear brakes, spring parking brakes or anywhere fast exhaust is needed.
A relay valve is a remote-controlled valve, mounted on the frame near the chambers it serves, that cuts lag on both application and release.
A relay valve gets reservoir air through a large supply line and delivers it at the same pressure as the foot valve's control signal (for example 20 p.s.i. in, about 20 p.s.i. out).
On release only the control line air vents at the foot valve; chamber air exhausts at the relay valve.
Relay valves serve two or four chambers and are mainly on rear axles.

Dual system with a failed section (p. 160)

If a line rupture empties the primary reservoir, the one-way check valve protects the secondary reservoir.
With a primary failure, only the steering axle brakes apply, so stopping takes longer.
With a secondary failure, the rear axle brakes still work but the steering axle brakes do not.
The compressor keeps pumping but its output escapes at the rupture.
If the low-air warning comes on, stop immediately and do not go on until the system is repaired.

Spring parking brakes

Why parking needs mechanical force, how spring brakes apply and release, compounding, caging, blended air and safety actuators.

Practise Spring parking brakes questions Flashcards Official chapter

Parking brakes (p. 160–161)

Parking with air pressure alone is unreliable and illegal; any leak or failed hose, diaphragm or valve could let the vehicle roll away.
Regulations require parking force to be held mechanically and be unaffected by loss of air pressure.
The most common air-system parking brake is the spring parking brake; the second type, the safety actuator, is found mostly on some highway coaches and intercity buses.

Spring parking brakes (p. 161–163)

A spring parking brake is an extra chamber piggy-backed on the rear of a service brake chamber, containing a powerful coil spring, a second diaphragm and an intermediate pushrod.
Spring parking brakes are mounted on rear axles only, never on steering axles.
The coil spring in most spring brake chambers exerts 1,500 to 2,000 pounds.
Service brakes are applied by air; spring brakes are applied by spring force and held off (released) by air pressure.
Spring brakes act through the same pushrod, slack adjuster and foundation brake as the service brake.
If system pressure falls below about 60 p.s.i. the spring brakes may start to drag, and at 20 to 45 p.s.i. (138 to 310 kPa) they may apply fully on their own.
In some systems spring brakes apply gradually as pressure drops and may start applying at 90 p.s.i. or higher.
Their effectiveness for stopping or holding depends on the brakes being kept in adjustment.
The dash parking brake control is usually a yellow button: push in to release the spring brakes, pull out to apply them; some vehicles use a flip switch.
Only qualified people should service spring brake chambers; keep away from a chamber with dents or cracks because the spring could break out.

Compounding (p. 164)

With spring brakes applied, up to about 2,000 lb is on the brake parts; a heavy service application adds up to about 3,000 lb more, for about 5,000 lb.
This adding of forces is compounding; it can damage slack adjusters, s-cams, chamber mounting bolts, shoe rollers, shoes and drums.
Release the spring parking brakes before making a heavy service application, such as during a pre-trip test.
Light applications under 30 to 40 p.s.i. to keep the vehicle from rolling while spring brakes are set or released are not harmful.

Manual release (caging) (p. 164–165)

Caging means mechanically compressing the spring with a release bolt so the spring brake is off; it is meant for mechanics doing repairs or, in an emergency, to tow a vehicle that has lost all air.
Always block the wheels before caging; once caged there is no parking force at that wheel.
A release bolt is inserted, given a quarter turn to lock, and the nut turned to compress the spring; instructions are usually on the housing.
After manually releasing spring brakes, call a tow truck to move the vehicle.

Spring brakes in dual systems: blended air (p. 165–167)

A two-way check valve feeds the parking brake control from whichever service reservoir has the higher pressure; this is called blended air.
The two-way check valve has two inlet ports, one delivery port and a free-floating shuttle that moves away from the higher-pressure inlet.
Blended air keeps the spring brakes from applying automatically if either reservoir loses all its air.
One way to test the two-way check valve: drain the primary reservoir and confirm secondary pressure does not bleed back into it.
An optional spring brake modulator senses primary loss and, when you press the foot valve, releases spring brake air in proportion to help the front brakes stop the vehicle.
All vehicles must meet federal emergency stopping standards even with a partly failed system; after stopping, park with the parking brake control valve.

Safety actuator parking brakes (p. 167–168)

Safety actuators, used on many buses and coaches, use a one-way locking mechanism instead of a coil spring, with one diaphragm for service and one for parking, and a separate parking reservoir.
Pulling the dash control applies air to the parking diaphragm and engages the lock, which holds the pushrod out even if all air is lost.
If more than 4 p.s.i. (27.6 kPa) has been lost from the parking reservoir, the brakes will not release until a heavy service application frees the lock.
Safety actuators cannot be compounded, and they apply automatically only if the parking reservoir loses pressure, not the service reservoirs.

Tractor-trailer air systems

Supply and control lines, glad hands, trailer emergency application, the tractor protection system, the trailer hand valve and bobtail tractors.

Practise Tractor-trailer air systems questions Flashcards Official chapter

Tractor-trailer air brake systems (p. 168–169)

A trailer air system has foundation brakes, chambers, reservoirs and valves but no compressor; it relies on the tractor for air and for apply/release commands.
The supply line (also called the emergency line) fills the trailer reservoirs at full tractor reservoir pressure.
The control line (also called the service line) carries the brake signal from the tractor.
Glad hands are the quick couplers on the air lines; blue usually marks the control line and red the supply line.
When not in use, fasten glad hands to dummy couplers or to each other to keep out dirt and stop chafing or bouncing.
Every trailer must have an emergency system that fully applies its brakes if it separates from the tractor.

Trailers with a relay emergency valve (p. 169–170)

Trailers without spring brakes use a relay emergency valve, which charges the trailer reservoir and relays the control signal at about the same pressure.
If supply line pressure is lost, the relay emergency valve applies full trailer reservoir pressure to the service chambers: "dynamiting" the trailer brakes.
Dynamiting also happens whenever the glad hands are disconnected or the driver closes the trailer air supply valve.
Safety standards require these dynamited brakes to stay applied at least 15 minutes; they hold only while the trailer reservoir keeps pressure.
Small leaks in trailers without spring brakes can let a parked trailer roll away, so always block the wheels.
Highway trailers use one reservoir and one relay emergency valve for a single or tandem axle; some tandem logging trailers have one per axle.

Trailers with spring parking brakes (p. 170–172)

A trailer spring brake valve fills the reservoir(s) and controls the spring brakes; a relay valve handles the service brakes.
Some systems fill the reservoir before releasing the spring brakes; others release the spring brakes first.
On loss of supply line pressure, the spring brake valve exhausts the spring chambers so the springs apply (dynamiting).
Signs the supply and control lines are reversed: the trailer spring brakes will not release with the dash control and the trailer service brakes do not work.
Always do a tug test after coupling, and check with a flashlight that the fifth wheel jaws are locked first.

Tractor protection (p. 172–173)

If the trailer breaks away, air rushes out of the broken supply line (and the control line when braking).
The tractor protection system is the dash trailer air supply valve plus a tractor protection valve usually behind the cab; all air to the trailer passes through it.
It shuts off air loss from the tractor in a breakaway so the driver keeps enough pressure to stop.
Some systems shut off immediately; some let tractor pressure drop to as low as 20 p.s.i. (138 kPa) before closing.
Safety standards require automatic shutoff of trailer air when tractor pressure falls to between 20 and 45 p.s.i. (138 and 310 kPa); with blended air this happens when the higher service reservoir reaches that range.
A peace officer may put the vehicle out of service if tractor pressure can drop below 20 p.s.i. without the trailer air supply valve closing.
A peace officer may put a trailer out of service if its brakes do not apply when the trailer air supply valve is closed.
Check the tractor protection system in every daily pre-trip inspection.
Most trailer air supply valves are an octagon-shaped red button on the dash.
With no trailer attached, the trailer air supply valve stays closed so no air is lost through the open glad hands.
If only the control line separates, nothing happens until the brakes are applied; then the protection system closes to save tractor air.

Hand valve and two-way check valves (p. 173–175)

A foot valve application sends about the same pressure to tractor and trailer brakes (for example 20 p.s.i. to both).
The hand valve (on the steering column or dash) applies the trailer brakes alone, for example when coupling; it is spring-loaded and returns to off when released.
Do not use the hand valve for normal or emergency braking; use the foot valve.
Never use the hand valve for parking: set the tractor parking brakes, close the trailer supply valve and block the trailer wheels.
Two-way check valves send the higher of the hand valve or foot valve pressure to the trailer control line.
A tractor equipped to tow adds a trailer air supply valve, tractor protection valve, hand control valve and a pair of two-way check valves.
In most dual systems the yellow parking brake button is interlocked with the red trailer supply button, so pulling yellow applies all tractor and trailer parking brakes.
Some tractors have a third, round blue button that controls the tractor parking brakes on their own.
With a tractor primary failure, the secondary still applies the tractor front brakes and signals the trailer brakes through the two-way check valves.

Bobtail tractors (p. 174)

Driving a tractor without a trailer is bobtailing.
With little weight on the drive axles, a bobtail tractor's rear brakes lock up easily, even with a light application.
A bobtail proportioning system reduces drive axle brake pressure by as much as 75 per cent when bobtailing, while the steering axle gets full pressure.
A bobtail tractor with this system stops shorter with better control, but needs more pedal pressure than normal.

Air brake adjustment

Pushrod stroke limits, checking manual slack adjusters by the applied and pry methods, adjusting them, automatic slack adjusters and common misconceptions.

Practise Air brake adjustment questions Flashcards Official chapter

It's critical, it's the law (p. 189)

The foundation brakes are the most important part of any braking system; even a well-designed air system cannot stop a vehicle whose brakes are out of adjustment.
Brake failures and runaways are almost never caused by the air system itself; missing maintenance or drivers not checking brakes daily is far more common.
Daily pre- and post-trip inspections, including checking and adjusting brakes, are mandatory, and the driver may be held responsible for badly adjusted brakes.
Federal and provincial law require you to check manual and automatic slack adjusters daily during the pre-trip inspection.
You must also check your brakes before descending steep grades posted with regulatory signs.
A maintenance crew may exist, but the driver is ultimately responsible for the brakes before the vehicle moves.
Operating with defective brakes, including excessive pushrod stroke, can bring a fine of up to $2,000.

S-cam brake released, applied and out of adjustment (p. 189–191)

The Type 30 chamber is the most common on trucks and trailers; it has a maximum stroke of 2½ inches (65 mm); a long-stroke Type 30LS has three inches.
A correctly adjusted brake strokes less than half its maximum when applied.
Slack adjustment means keeping chamber pushrod travel within tolerance so the brakes work.
Pushrod travel is the distance the pushrod comes out of the chamber when the brakes apply.
Correct running clearance between lining and drum is only a few thousandths of an inch, about three sheets of paper.
Check pushrod travel at least daily; brakes on the same axle should have similar travel left and right.
A brake with excessive travel may still seem to work with a cool drum and normal pressure, giving false security.
Cast iron drums expand when hot, so the chamber strokes farther; a badly adjusted brake can bottom out and lose most of its power.
On long downgrades, hot drum expansion with poorly adjusted brakes can cause total loss of braking and a runaway.

Checking s-cam brakes with manual slack adjusters (p. 191–193)

Park safely with wheels blocked, air at full pressure, spring parking brakes released, engine off so you can hear leaks.
Applied stroke method (used by roadside inspectors): mark the pushrod at the chamber (or measure clevis pin to chamber face) with brakes released and reservoir at least 100 p.s.i.
Then hold a full application of 90 to 100 p.s.i. (620–690 kPa) and measure again; usually two people are needed unless you have a device to hold the brakes on.
A good applied stroke is 1 to 1½ inches (25–38 mm); more than 1¾ inches (45 mm) means the brake needs adjusting.
Pry method: with system air over 100 p.s.i. and parking brakes released, push the pushrod fully in, mark it, pry it out with a bar and measure.
A good free stroke is ½ to ¾ inch (12–20 mm); more than ¾ inch (20 mm) means adjustment is needed.
These limits are maximums for a Type 30 clamp chamber; adjust when measurements approach them.
New pushrods have a marking, usually red, that shows when travel is excessive; if it is visible the brake is dangerously out of adjustment; do not wait for it to appear.
Tools: flashlight, chalk or marker and ruler, a pry tool, and a wrench for manual slack adjusters; wear sturdy clothing, hard hat and eye protection.
Also look for s-cam bushing wear, s-cam spline wear, slack adjuster play (worn gear) and clevis pin wear.

Adjusting a manual slack adjuster (p. 194–195)

Most manual slack adjusters have a spring-loaded locking sleeve that must be pressed in and held while turning the adjusting bolt, usually with a 9/16-inch wrench.
Turning the right way makes the camshaft rotate in the same direction as when the brakes apply.
If turning the bolt pulls the pushrod out of the chamber, you are turning the wrong way; stop.
The pushrod and slack arm should not move in or out while you turn the bolt; if the pushrod goes into the chamber, the previous adjustment was done wrong.
Turn until solid resistance (linings touching the drum), then back off about 1/3 of a turn and make sure the locking sleeve re-engages.
The correct direction may be clockwise or counter-clockwise; on tandems one axle often adjusts opposite to the other.
After adjusting, re-measure free stroke to confirm clearance.

Automatic slack adjusters (p. 195–197)

All air-braked commercial trucks and trailers have been built with automatic slack adjusters since 1996.
They adjust themselves during normal braking but must still be checked at every pre-trip inspection.
Excessive stroke with an automatic slack adjuster usually means it failed, was installed wrong, or there is a foundation brake problem; it needs a qualified mechanic.
Manually adjusting an automatic slack adjuster is dangerous: it gives false security, the adjuster soon resets, and repeated adjustment wears it out and can mask other problems.
Manufacturers generally recommend a mechanic check them at every chassis lube, every 40,000 km or every three months, whichever comes first.
Check stroke with a 90 to 100 p.s.i. application; without an application gauge, shut the engine off and pump reservoir pressure down to 90–100 p.s.i., then make a full application.
Automatic adjuster strokes are usually slightly longer; on a Type 30 the brake needs repair if free stroke exceeds ¾ inch (20 mm) or applied stroke exceeds two inches (50 mm).
Emergency adjustment is a last resort only (for example, to reach a service depot); record it on the post-trip report.
Hexagonal bolt type: turn clockwise until the lining contacts the drum, then back off ½ turn; ratcheting is normal.
Square bolt type: disengage the spring-loaded pawl first (pry up the button about 1/32 inch or remove cap, spring and pawl), turn counter-clockwise to contact, then ½ turn clockwise.

Air brake adjustment misconceptions (p. 197–198)

False: an 8 to 12 p.s.i. pressure drop on a full application shows adjustment; large reservoirs and coarse gauges make this useless.
False: a 90-degree slack adjuster angle when applied proves good adjustment; the angle depends more on pushrod length and may vary plus or minus 10 degrees by design.
False: clockwise always sets up the brakes; it depends on the adjuster's orientation.
False: open parking and trailer supply valves prove spring brakes are off; some stay open with as little as 20 p.s.i., so have 90 to 100 p.s.i. and all parking brakes released before checking.
False: manual slack adjusters are better; a Transport Canada study found vehicles with manual adjusters were put out of service 150 per cent more often.
It is illegal in B.C. to retrofit manual slack adjusters on a vehicle built with automatic ones.
There is no reliable substitute for physically checking brake adjustment.

Trip inspections and reports

When inspections are required, which vehicles need written reports, cargo securement re-checks, report rules, pre-trip procedure, brake checks before hills and en route checks.

Practise Trip inspections and reports questions Flashcards Official chapter

You're responsible, vehicle condition (p. 199–200)

The driver is responsible for making sure all safety features work before driving.
Commercial vehicles under the National Safety Code must be inspected before first use each day (pre-trip) and at the end of the day's final trip (post-trip), as required by the Motor Vehicle Act Regulations.
The driver or another person named by the carrier may do the inspection; driver and carrier share responsibility.
Daily written inspection reports are required for: buses, school buses, special activity buses, special vehicles or limousines seating more than 10 including the driver; two-axle trucks or tractors licensed over 14,600 kg GVW; trucks or tractors towing a trailer licensed over 8,200 kg GVW.
You may be fined for failing to carry a trip inspection report; an unsafe vehicle may bring a fine and/or be put out of service.
Pre-trip inspections prevent costly delays and crashes from mechanical failure.

Cargo securement inspections (p. 200, 233)

Under the NSC, all vehicles carrying cargo on a highway, whatever their weight, must be inspected for cargo securement, including equipment such as tailgates, doors, tarps and the spare tire.
Re-inspect cargo securement within 80 km of where the cargo was loaded.
After that, re-inspect at the earliest of a change in duty status, three hours of driving, or 240 km since the last check.
Record cargo securement inspections in your daily log.
No inspection is needed if the cargo is sealed and you were ordered not to open it, or if it is inaccessible.

Written report requirements (p. 201–202)

A trip inspection report must show plate or unit numbers, list every defect that may affect safe operation or state that none was found, be dated, be signed by the inspector and be completed before the first trip of the day.
On multi-day trips, a new report is due no later than the first rest stop of each later day.
If you couple to another trailer during the day, carry that trailer's report for the day or complete one.
For each defect, the report must say it was corrected or that no correction is needed; a defect that does not affect safety may wait but must still be recorded.
With more than one driver, only one need sign if all agree; if they disagree, all must sign and describe the disagreement.
Trip inspection reports must be given to the carrier within 20 days.
Division 37 of the Motor Vehicle Act Regulations sets B.C.'s trip inspection rules and exemptions.
On the road test the examiner gives you a trip inspection report form; part of your mark is how completely and accurately you fill it in.

Conducting a pre-trip inspection (p. 203)

Any order is allowed, but use the same order every time so nothing is missed.
Before you begin: park in a safe spot away from traffic, on level ground if possible, set the parking brakes, shut off the engine and block the wheels front and back on the same axle.
Walk counter-clockwise around the vehicle so you face oncoming traffic.
Look under the vehicle for leaks as you approach; leaks and body damage are easier to see from a distance.
Take the keys out of the ignition before working underneath.
Tools: flashlight, tire pressure gauge, chalk and ruler, pry tool, wrench, and a watch or timer for air leakage and build-up; wear sturdy clothing, hard hat and eye protection.
Components you cannot safely reach on low or air-suspended vehicles should be checked by a mechanic during maintenance.
A peace officer may put a vehicle out of service if drum brake linings are under 1/4 inch (6.4 mm) or air disc pads under 1/8 inch (3.2 mm).
Rust streaks at wheel nuts may mean loose nuts; shiny areas at spoke wheel clamps may mean the rim is slipping.
Check that a fire extinguisher's label date is valid; typical emergency equipment is flags or flares, a first aid kit and a fire extinguisher.

Pre-hill, in-service, en route and post-trip inspections (p. 232–235)

Where signs are posted before steep or long downgrades, stop in the pullout and inspect the brakes and load security before going on; you may be fined for not stopping.
At a brake check: compressor keeps full pressure, no audible leaks, glad hands and lines secure, drums and hubs not overheated, pushrod travel within limits, even with automatic slack adjusters.
With hydraulic brakes, check pedal reserve, drum temperature and fluid leaks before the hill.
Drivers of heavy non-commercial vehicles such as motorhomes are not required to stop at brake checks but may use the pullouts.
In-service checks: watch the air gauges, the low-air warning and how the brakes feel.
En route checks cover tires (heat, damage), wheels and nuts, brakes and hubs, trailer coupling, cargo and dangerous goods placards, and suspension and driveline.
Do not keep driving if smoke comes from an oil-filled hub or the hub is too hot to touch.
At the end of the day's final trip, inspect the vehicle and complete a trip inspection report; it can be added to that day's pre-trip report.
Commercial trailers 2.05 m wide or more need reflective markings to the rear and sides.
Under the fuel-efficiency chapter, en route inspections including tires and cargo are recommended at least every three hours.

Class 1 pre-trip inspection

The Class 1 road test pre-trip: timing, slack adjuster set-up, fifth wheel and landing gear checks, leakage limits with trailers, tug tests and breakaway checks.

Practise Class 1 pre-trip inspection questions Flashcards Official chapter

Class 1 tractor-trailer pre-trip (p. 204)

You should be able to complete the Class 1 pre-trip inspection in less than 45 minutes.
You must show you can set up a slack adjuster during the Class 1 pre-trip test.
Heavy trailer endorsement (code 20) applicants follow the Class 1 pre-trip but leave out the air brake steps.
Before you begin: set the parking brakes, shut off the engine and block the wheels.
Class 1 applicants must also complete and submit a written trip inspection report.

Class 1 mechanical circle check (p. 209–212)

Check lights in a counter-clockwise circle: left signal, low beams, tail, plate and clearance lights first; then right signal, high beams and brake lights.
Carry a rag to wipe lenses and reflective tape.
Fifth wheel: plate flush with the trailer apron (no daylight), slider locked with room for the trailer to turn, locking jaws closed around the kingpin; check with a flashlight from both sides and underneath.
Pintle or ball hitch: not worn, lock closed, chains or cables free of stress cracks and weld breaks and attached to both units.
Landing gear: fully raised, no missing parts, crank handle secured.
Check the cab protector is secure to the frame, the cargo lift is retracted and latched, load security devices are tight, trailer doors latched.
Check for a CVIP inspection decal on the trailer body and tractor.
Check drive line u-joints for free play and leaks, and that air tanks are securely mounted.
Fuel tanks, caps and lines, exhaust, batteries and storage compartments must be secure on both sides of the tractor.

Class 1 leakage, tug and response tests (p. 212–213)

Back in the cab, air must be at least 100 p.s.i. with parking brakes released before the leakage test.
Hold a 90 to 100 p.s.i. application for one minute: no more than 4 p.s.i. per minute loss with one trailer, 6 p.s.i. with two.
Then set the parking brakes and remove the wheel blocks.
Tug test 1: release the tractor parking brakes, keep the trailer brakes applied, and in low gear gently tug; the trailer brakes must hold.
Tug test 2: apply the tractor parking brakes, open the trailer supply valve to release the trailer brakes, and gently tug; the tractor brakes must hold.
Then roll ahead slowly and test the foot brake, then the hand valve for trailer brake response, then steering wheel play.
A trailer without air brakes: check its breakaway system; for most electric brakes, disconnect the electrical cable, pull the pin from the breakaway switch and confirm the brakes apply, then reinstall.
Inspect double trailers, their couplers and air systems the same way.

Class 1 road test and MELT (p. 7–13)

Class 1 covers semi-trailer trucks and any other vehicle or combination except motorcycles; minimum age 19.
The Class 1 knowledge test includes all the air brake knowledge test material; Class 1 applicants do not take the separate single-unit air brake test.
Class 1 Mandatory Entry Level Training (MELT), required since October 18, 2021, includes air brake training, so no separate air brake course is needed.
The Class 1 road test takes about two hours and includes coupling and uncoupling.
Class 1 test vehicle: loaded tandem or tridem tractor-trailer with air brakes, at least 28,000 kg on the road, semi-trailer at least 13 m (7.5 m pintle-hitch trailer).
The Class 1 combination air brake endorsement comes through the Class 1 knowledge test, MELT and an air brake pre-trip on the Class 1 road test (ICBC air brake page).

Air brake pre-trip test

The air brake pre-trip on the road test: draining reservoirs, governor cut-out and cut-in, low-air warning, trailer supply valve closing, build-up time and leakage limits.

Practise Air brake pre-trip test questions Flashcards Official chapter

Air brake pre-trip test requirements (p. 199, 203)

Commercial and heavy trailer applicants do a pre-trip inspection on the road test; if the vehicle has air brakes, or for an air brake endorsement, you also inspect the air brake system.
With manual slack adjusters you must show you can adjust a brake; with automatic slack adjusters you must explain how manual adjusters are adjusted.
Air-brake-endorsement-only applicants complete just the air brake pre-trip (the red-coded portions of the Class 1 and 3 inspections).
On the test, assume the vehicle has not been driven that day; point to or touch each item and say what you are checking for.

Under hood and in cab (p. 205–208, 215–217)

Drain the reservoirs; for the road test only the supply reservoir must be drained, but all reservoirs should be drained daily.
Watching the gauges while draining helps tell the supply reservoir from the primary and secondary.
Check the compressor is securely mounted and its lines have no kinks, leaks, cuts or abrasions; check belt tension.
After draining only the supply reservoir, if the primary or secondary gauges also lost pressure, a one-way check valve may not be working.
Check that the compressor stops pumping (governor cut-out) between 105 and 135 p.s.i. (724 and 931 kPa).

Air brake system test, single unit (Class 3) (p. 218)

Pump the brake pedal down to about 80 per cent of maximum (100 p.s.i. if maximum is 125) and confirm pressure starts to build (governor cut-in); cut-in must happen before pressure falls below 80 p.s.i. (552 kPa).
Pump down further and check the low-air warning comes on at or above 60 p.s.i. (414 kPa).
Pump down below 50 p.s.i., then check pressure rebuilds from 50 to 90 p.s.i. (345 to 620 kPa) within three minutes at fast idle (1,000 to 1,200 r.p.m.).
Release the spring parking brakes if they applied during the pump-down.
In some systems one service reservoir fills first and the other starts at about 85 to 95 p.s.i.; either way, 50 to 90 p.s.i. must take no more than three minutes.

Air brake system test, tractor-trailer (Class 1) (p. 208)

After governor cut-in and low-air checks, keep pumping down and check the trailer air supply valve closes when the highest reservoir gauge reads 20 to 45 p.s.i. (138 to 310 kPa); the parking brake valve may or may not also close.
Shut off the engine and confirm the trailer brakes have applied.
Disconnect both glad hands and check no air escapes from the tractor or trailer through them.
Make a foot brake application and listen that no air escapes through the supply or control line.
Reconnect, check the electrical connection and that lines have enough slack for turns and are not chafing, then check the 50-to-90 p.s.i. build-up within three minutes.

Leakage test (p. 213, 221)

Do the leakage test with the engine off so you can hear leaks, air at least 100 p.s.i. and parking brakes released (to avoid compounding).
Make a full application of 90 to 100 p.s.i. (620 to 690 kPa) and hold it one minute.
Single-unit truck: after the initial drop, loss must not exceed 3 p.s.i. (20.7 kPa) per minute.
Tractor and one trailer: no more than 4 p.s.i. (27.6 kPa) per minute; with two trailers, no more than 6 p.s.i. (41.4 kPa) per minute.
There must be no audible air leaks.

Brake response, tug and steering tests (p. 213, 221, 228)

Single unit: in low gear gently tug against the parking brakes (they must hold), release, roll ahead slowly and apply the foot brake, then check steering wheel play.
Check brake adjustment while underneath the vehicle; check foundation brakes, chambers, slack adjusters, s-cams, drums, linings and air lines at each wheel.
Check that brake chamber mounting and clamps are secure, no cracks, corrosion or holes, and no audible leaks.
Check drums are not cracked and linings or drums are not contaminated with oil or grease.

Written in our own words from: Driving Commercial Vehicles