Supplemental Brakes +13Quebec · CDL · English

Before descending a steep grade, shift into a gear that maintains control. Manufacturers state the greatest engine braking effect is in first gear, and general practice is to shift into first before starting down a steep grade, staying in that gear all the way down. The lowest appropriate gear provides engine compression that helps control speed — effective with standard or automated manual transmission.

• ✓Greatest engine braking effect is in first gear; shift down before descending a steep grade
• ✓Stay in the selected low gear all the way down
• ✓Engine compression works with both standard and automated manual transmissions

Before a steep grade, shift into a gear that maintains speed control. Manufacturers state the greatest engine braking effect comes in first gear; general practice is to shift into first before a steep grade and stay there all the way down. Engine compression works with standard or automated manual transmission.

• ✓Shift into the controlling gear before the steep grade, not during
• ✓Greatest engine braking effect is in first gear (general practice on steep grades)
• ✓Stay in the chosen low gear all the way down
• ✓Engine compression is effective with standard or automated manual transmission

When loaded, supplemental brakes help maintain desired speed without overusing service brakes. Ensure they work before starting downhill by activating the switch and releasing the accelerator. Supplemental brakes are most effective when the engine turns at maximum RPM for a given gear. At the bottom of the hill, increase speed and shift to the appropriate gear.

• ✓Check the supplemental brake works before descending by activating the switch and releasing the accelerator
• ✓Supplemental brakes are most effective at maximum engine RPM for a given gear
• ✓Supplemental brakes reduce reliance on service brakes when loaded

Automated manual transmission functions like manual but is electronically synchronized, downshifting or holding gear only when there's no risk of mechanical failure. You can select a lower gear than the highest automatically chosen gear to gain engine compression when descending; this prevents automatic upshifts. Watch engine RPM to avoid over-revving. On steep or slippery grades, a lower gear prevents frequent or unplanned gear changes.

• ✓Automated manual transmission only downshifts/holds gear when there's no mechanical failure risk
• ✓Select a lower gear for engine braking downhill and watch RPM to avoid over-revving
• ✓Choosing a lower gear prevents unplanned shifts on steep or slippery grades

Supplemental brakes help maintain desired speed without overusing service brakes, especially when loaded. Check they work before descending by activating the switch and releasing the accelerator. They are most effective when the engine is turning at maximum RPM for a given gear. At the hill's bottom, increase speed and shift to the appropriate gear.

• ✓Supplemental brakes reduce reliance on service brakes when loaded
• ✓Check supplemental brakes work before starting downhill
• ✓Supplemental brakes are most effective at maximum RPM for a given gear
• ✓Activate the switch and release the accelerator to engage

Automated manual transmission functions like manual but is electronically synchronized to downshift or hold gear only when there is no risk of mechanical failure. You can select a lower gear than the highest automatic gear for engine compression when descending—useful on steep or slippery grades—but watch that engine RPM does not get too high.

• ✓Automated manual transmission downshifts/holds gear only if no mechanical failure risk
• ✓You can manually select a lower gear for engine compression when descending
• ✓Choosing a lower gear prevents unplanned upshifts on grades
• ✓Watch engine RPM does not get too high in a lower gear

Drivers must ensure an inspection was performed within 24 hours before driving, with a new one required if not done by a designated person.

• ✓Drivers must ensure an inspection was performed within the 24 hours prior to driving
• ✓A new inspection is required if the check was not done by a person designated by the operator, even if fewer than 24 hours have elapsed
• ✓Drivers must plan activities to perform a new check before 24 hours elapse, except for certain vehicles with different limits

Certain vehicle types have alternate validity rules including road tests after repairs, fire vehicles, buses, and transit vehicles.

• ✓No check required for a road test after repairs if within 15 km radius, no goods, no passengers (except test personnel), and the last report or work order is on board
• ✓Fire department vehicles need a check within 24 hours before an outing or on return; if in station, at least once every 7 days
• ✓For buses, minibuses and emergency vehicles (except fire), Saturdays, Sundays and statutory holidays don't count in the 24-hour validity if parked
• ✓Urban transit buses/minibuses: check valid 48 hours if parked indoors, or 24 hours from being put into operation, whichever elapses first (must be done by designated person)

There is a brake chamber near each wheel. Air from the service reservoirs pushes a diaphragm connected to a push rod. In a drum brake, the push rod operates a slack adjuster that turns a camshaft; the S-cam makes the brakes clamp. There are single chambers (service brake) and double chambers (service + parking brake).

• ✓A brake chamber is located near each wheel
• ✓Air pushes the diaphragm connected to the push rod
• ✓Single chamber = service brake; double chamber = service + parking brake
• ✓In drum brakes the push rod operates the slack adjuster and S-cam

Parking brakes are mounted only on rear wheels of tractor/truck/bus (requiring double chambers on at least one axle) and on trailer/semi-trailer wheels except most auxiliary lift axles. A parking brake is always paired with a service brake and uses a powerful spring. Pulling up empties air so springs apply the brake; pushing down fills air, compresses the spring, and releases the wheels.

• ✓Parking brakes use a powerful spring and are always paired with a service brake
• ✓Mounted on rear wheels of tractor/truck/bus and trailer wheels
• ✓Pull up = air out, spring applies brake; push down = air in, spring compressed, wheels free
• ✓Spring also activates the emergency brake if a problem arises

A drum brake uses brake shoes with linings pressing against the inside of a drum on the wheel. S-cam drum brakes are the most common on heavy vehicles; an S-shaped cam pulls the shoes apart. Friction produces heat; overheated linings lose effectiveness through misuse or overuse.

• ✓Drum (S-cam) brakes are the most common on heavy vehicles
• ✓S-shaped cam pulls the brake shoes apart against the drum
• ✓Overheated linings lose effectiveness

A disc brake uses a disc on the hub with linings (pads) held by a caliper that rub both sides of the disc. Disc brakes are most common on motor coaches and increasingly used elsewhere. Compared to drum brakes, they use less air (smaller chamber) and their efficiency is less impaired at high temperatures.

• ✓Disc brakes use a caliper pressing pads on both sides of a disc
• ✓Consume less air than drum brakes
• ✓Less likely to lose efficiency at high temperatures

All parties involved in a vehicle's operation share responsibilities for its mechanical condition and inspection compliance.

• ✓Owners must maintain vehicles in good mechanical condition and have reported defects repaired
• ✓Operators must ensure the driver or designated person conducts the circle check per regulatory requirements
• ✓Drivers must perform the circle check per requirements (unless accepting another's inspection) and report defects detected during a trip

List 1 applies to heavy vehicles other than buses, minibuses or motor coaches. Coupling minor defects include missing/broken/loose fastener components and damaged/insecure safety fasteners. Major defects (some applying only when coupled) include bent kingpin/coupling plate, fifth wheel movement, and locking pin failures.

• ✓Minor: fastener component(s) of the coupling device missing, broken or loose
• ✓Major: coupling plate or kingpin bent, cracked, or not securely fixed
• ✓Major: more than 20% of coupling mechanism fasteners damaged or missing
• ✓Major: 25% or more of locking pins missing or not working
• ✓Major: coupling mechanism not properly closed or locked

Reinforced exam facts: With hydroplaning, do NOT apply the brakes. A blowout in one dual wheel on a semi-trailer is NOT strongly felt. During a skid, turn the wheel in the same direction as the skid. Hydraulic brakes CAN be affected by overheating. Emergency brakes take over when air pressure in reservoirs is insufficient.

• ✓Do not brake during hydroplaning; steer in the same direction as a skid
• ✓A dual-wheel blowout is not strongly felt; hydraulic brakes are affected by overheating
• ✓Emergency brakes take over when compressed air in reservoirs is insufficient

Sit in the driver's seat and inspect the windshield for transparency, damage, or cracks that hamper visibility while driving. Clear the dashboard and windshield of obstructing objects for best visibility.

• ✓Defect 11.1 (minor): The windshield is tarnished, cloudy, or broken in a way that reduces the driver's vision of the road or road signs/signals
• ✓Inspect from the driver's seat and clear obstructing objects

For all outside mirrors, inspect mounting and check for sharp edges (pointed/cutting edges that could injure). Mandatory mirrors: every vehicle needs an outside mirror on both sides; school buses/minibuses also need a front-mounted convex outside mirror on both sides. Ensure each is adjustable and stays positioned for safe driving.

• ✓Defect 11.3 (minor, all mirrors): An outside rearview mirror is not securely mounted or shows a sharp edge
• ✓Defect 11.2 (minor, mandatory mirrors): A mandatory mirror is missing, broken, cracked, tarnished, or cannot be adjusted/remain in the desired position
• ✓School buses and minibuses require front-mounted convex outside mirrors on both sides

Sit in the driver's seat and inspect the windshield and side windows for transparency, damage, cracks, or obstructions that hamper visibility. School buses and minibuses must also check the side windows directly behind the driver's compartment.

• ✓Minor defect (11.1): the windshield or a side window is tarnished, cloudy, obstructed, crazed or cracked reducing the driver's vision of the road or road signs/signals
• ✓Minor defect (11.4, school buses/minibuses): a side window directly behind the driver's compartment reduces the driver's vision

Check the condition of side windows on each side of the driver's compartment from the driver's seat for transparency, damage, cracks, or obstructions (e.g. opaque stickers). School buses and minibuses must also check side windows directly behind the driver's compartment.

• ✓Defect 11.1 (minor): A driver's compartment side window is tarnished, cloudy, obstructed, crazed, or cracked reducing driver's vision
• ✓Defect 11.4 (minor, school buses/minibuses): A side window on either side and directly behind the driver's compartment is similarly impaired

All bus drivers except urban transit are governed by the Regulation respecting hours of driving and rest, and must obey other jurisdictions' rules when travelling outside Québec. Under the Regulation respecting safety standards for road vehicles, a bus driver must perform a circle check within 24 hours before taking the bus out, or read and sign a report of a check done within the preceding 24 hours.

• ✓Non-urban-transit bus drivers are subject to hours of driving and rest rules
• ✓Obey other jurisdictions' regulations when travelling outside Québec
• ✓A circle check must be done within 24 hours before taking a bus out
• ✓If someone else did the check, the driver must read and sign the report

Drivers carrying passengers must know applicable laws. The principal enforcement bodies are the Société de l'assurance automobile du Québec, the Ministère des Transports du Québec, and the Commission des transports du Québec. Beyond the Highway Safety Code, passenger drivers are subject to the Transport Act, Bus Transport Regulation, and the Regulation respecting road vehicles used for transporting school children.

• ✓Enforcement bodies: SAAQ, Ministère des Transports, Commission des transports du Québec
• ✓The Transport Act requires school bus drivers to hold a certificate of competency
• ✓The Bus Transport Regulation governs permits for transporting passengers by bus
• ✓School bus manufacturing/outfitting/use standards come from a dedicated regulation

The pressure conversion table converts psi to kPa and bar, useful for interpreting brake air leak limits and tire pressures. Approximately 1 psi equals 6.9 kPa (0.07 bar).

• ✓1 psi ≈ 6.90 kPa ≈ 0.07 bar; 5 psi ≈ 34.5 kPa (relevant to a 35 kPa air leak limit)
• ✓Use the table to convert brake air leak thresholds and tire pressures between imperial and metric units

Air brakes react more slowly than hydraulic brakes because air is compressible. Valves (including the relay valve) keep air on standby to reduce reaction time. It takes about one-half second for air to pass through the system; at 90 km/h a vehicle covers 12.5 m during this time.

• ✓Air brakes react slower than hydraulic brakes (air compressible)
• ✓Relay valve keeps air on standby to reduce reaction time
• ✓Takes ~0.5 second for air to pass through the system
• ✓At 90 km/h vehicle travels 12.5 m in that half-second

The compressor draws in outside air, sends it through an air dryer to the supply reservoir, then to service reservoirs. Pressing the brake pedal sends air to each brake chamber, exerting force against drums or discs. The system uses air force with the lever principle to amplify a slight pedal pressure into strong braking.

• ✓Air path: compressor → air dryer → supply reservoir → service reservoirs → brake chambers
• ✓Slight pedal pressure amplifies into large braking force
• ✓Uses air force combined with lever principle

On drum brakes the diaphragm moves the push rod which operates the slack adjuster, rotating the S-cam to pull shoes apart against the drum. On disc brakes the diaphragm pushes a lever exerting force via a piston on a pad; a counterforce moves the caliper pushing the opposing pad against the disc.

• ✓Drum: diaphragm → push rod → slack adjuster → S-cam → shoes clamp drum
• ✓Disc: diaphragm → lever → piston → pad, caliper pushes opposing pad
• ✓Both stop the wheel from turning freely

Braking power results from several mechanical factors combined. There is a limit to braking capacity set by the maximum air pressure the service reservoirs can supply and, for drum brakes, proper slack adjuster adjustment.

• ✓Factors: compressed air pressure, brake chamber size, slack adjuster length, cam rotation (drum)
• ✓Braking capacity limited by max reservoir air pressure
• ✓Drum brake capacity also limited by proper slack adjuster adjustment

The semi-trailer's service brakes operate at the same time as the tractor's. Pressing the brake pedal activates brakes on all of the vehicle combination's wheels.

• ✓Semi-trailer service brakes operate at the same time as the tractor's
• ✓Brake pedal activates all wheels in the combination

The compressor draws in outside air, sends it through an air dryer to the supply reservoir, then to the service reservoirs. Pressing the brake pedal sends air to each wheel's brake chamber, driving the shoes against the drums or discs. Even slight pedal pressure yields large braking force through amplification.

• ✓Air path: compressor → dryer → supply reservoir → service reservoirs → brake chambers
• ✓Pedal pressure sends air to each wheel's brake chamber
• ✓The system amplifies the driver's pedal force

In a drum brake the diaphragm pushes the push rod which operates the slack adjuster, rotating an S-cam via a camshaft to spread the shoes against the drum. In a disc brake the diaphragm pushes a lever that forces a pad against the disc, with an equal counterforce moving the caliper to press the opposing pad.

• ✓Drum: diaphragm → push rod → slack adjuster → S-cam spreads shoes
• ✓Disc: diaphragm → lever forces pad; caliper presses opposing pad
• ✓Both stop the wheel from turning freely

The semi-trailer's service brakes operate at the same time as the tractor's, so pressing the brake pedal brakes all wheels of the combination.

• ✓Semi-trailer service brakes operate at the same time as tractor's
• ✓Pressing the brake pedal brakes all wheels of the combination

Only wheels on weight-bearing axles must be checked (auxiliary lift axle recommended). Inspect visible parts: on spoke wheels the spokes, discs, and rims; on disc wheels the entire wheel, especially around the bolts.

• ✓Defect 12.C (major): A wheel is cracked, broken, or shows indication of repair or welding
• ✓Defect 12.C (major): One of the stud holes is widened or oval-shaped

Check the presence and condition of wheel fasteners (bolts, wheel rim clamps, wheel studs and nuts) around the vehicle.

• ✓Defect 12.B (major): A wheel fastener is missing, cracked, broken, or not securely fixed
• ✓Inspect bolts, rim clamps, studs, and nuts around the vehicle

Check for leaks and oil level in wheel hubs. Check lubricant through the hub sight glass if equipped (do not remove the filler cap). Check for oil/grease traces on wheels or the ground. Insufficient lubricant can cause the wheel to come off. Leaks may be caused by a broken/missing plug, filler cap, or axle cap, or a damaged seal.

• ✓Defect 12.A (major): Wheel bearing lubricant is not visible through a sight glass, or is absent regardless of sight glass
• ✓Defect 12.1 (minor): Lubricant below minimum level when visible through a sight glass; or lubricant leakage other than sweating
• ✓Only check oil level if the hub has a sight glass; do not remove the axle cap to check

Check for leaks (seals) and oil level in the wheel hubs. Only check oil level if the hub has a sight glass (usually on steer axle and some trailer/semi-trailer wheels); do not remove the filler cap or axle cap. Check for oil/grease traces on wheels or the ground. Insufficient lubrication can cause a wheel to come off.

• ✓Major defect (12.A): wheel bearing lubricant is not visible through a sight glass, or lubricant is absent regardless of sight glass
• ✓Minor defect (12.1): lubricant is below minimum when visible through a sight glass, or there is lubricant leakage other than sweating

Check the solidity of the spare wheel support and fasteners behind the cab or under the vehicle. You need not go underneath — just visually confirm the support appears to securely hold the spare wheel.

• ✓Defect 12.2 (minor): The spare tire support or fasteners cannot retain the solidly fixed spare wheel
• ✓A visual check of the support is sufficient; going under the vehicle is not required

Liquid movement combined with a high centre of gravity creates special driving conditions. When a tank is only partly filled, sudden steering or braking directly affects vehicle control.

• ✓Avoid sudden steering or braking movements when a tank is only partly filled
• ✓Liquid movement in a partly filled tank can directly affect control of the vehicle

Liquid density and temperature must be considered when filling to comply with the manufacturer's maximum load on the certification plate. Some liquids expand and dense liquids like sulfuric acid can exceed weight limits.

• ✓Never fill a tank to more than 70% of its capacity
• ✓Account for liquid density and temperature to comply with the certification plate load limit
• ✓Dense liquids such as sulfuric acid can cause the vehicle to exceed authorized weight limits

When braking, liquid forms a wave that travels forward, strikes the tank front and rebounds rearward, exerting thrust. Baffles (perforated walls) reduce front-to-back surge but side-to-side displacement can still overturn the vehicle.

• ✓Braking creates a forward liquid wave that exerts thrust on the tank ends
• ✓Baffles reduce fore-aft surge but do NOT prevent side-to-side displacement that can overturn the vehicle
• ✓Reduce speed well below the maximum limit, especially in slippery conditions and on curves/exits/turns

In multi-compartment tanks, liquid must be distributed evenly in each compartment, with balanced front-to-rear weight for safe loading and unloading.

• ✓Distribute liquid evenly in each compartment of a multi-compartment tank
• ✓Avoid placing too much weight at the front or the rear

A minor defect does not pose an immediate safety risk but can worsen, requiring repair within a set timeframe.

• ✓A minor defect does not pose an immediate risk to driver or road user safety but could deteriorate quickly
• ✓A vehicle with a minor defect cannot be operated if repairs are not performed within 48 hours

A major defect poses an immediate safety risk and results in an absolute prohibition from operation.

• ✓A major defect poses an immediate risk to safety
• ✓It is prohibited to operate or allow operation of a vehicle with a major defect

Reporting timelines differ for minor versus major defects, with major defects requiring immediate action.

• ✓A minor defect must be recorded and notified to the operator before the next circle check or within 24 hours, whichever comes first
• ✓A major defect must be immediately recorded and reported without delay to the operator
• ✓A major defect constitutes a prohibition from operation — the vehicle may not be driven or put into operation

Minor steering defects include misplaced steering column/adjustable wheel not staying set, incorrect power steering fluid level, and a cut pump belt. Major defects include steering column/wheel misplacement showing separation risk and inoperative power steering.

• ✓Minor: incorrect power steering fluid level; pump belt cut
• ✓Major: steering column/wheel misplacement showing risk of separation
• ✓Major: power steering inoperative

Minor defects include cracked side rails or cross members and missing/insecure fixed body components. Major defects include side rails that might break, sagging that makes mobile parts touch the body, and more than 25% of sliding bogie locking pins missing or not engaged.

• ✓Minor: side rails cracked or cross members cracked/broken
• ✓Major: side rails might break
• ✓Major: more than 25% of sliding bogie locking pins missing or not engaged

Minor defects include an improperly operating accelerator or clutch and a horn not operating properly. A major defect is when the engine fails to return to idle when the accelerator is released.

• ✓Minor: accelerator or clutch not operating properly; horn not working
• ✓Major: engine fails to return to idle when accelerator is released