Red Seal Truck and Transport Mechanic key terms

A safety procedure in which energy sources are shut off, isolated and locked, and a tag names the person working, so the equipment cannot be re-energized until the repair is finished.

Specialized gear such as safety glasses, gloves, hearing protection and steel-toe boots worn to reduce injury from hazards like flying debris, chemicals, noise and heavy parts.

A written or electronic document that authorizes a repair and records the vehicle, the complaint, the tasks, parts and labour, so the job can be tracked and billed.

A calibrated tool that applies a measured twisting force to a fastener so it is tightened to the manufacturer's specification without being over-stressed or left loose.

An exhaust-driven turbine on a shaft with a compressor that forces extra air into the cylinders, letting the engine burn more fuel and produce more power.

A valve that routes exhaust gas around the turbine to cap boost pressure, protecting the engine and turbocharger from over-boost at high speed or load.

A replaceable sleeve fitted into the engine block that forms the cylinder bore the piston runs in; renewing it restores a worn bore without replacing the block.

The clearance between the valve stem tip and the rocker arm or cam follower, which allows parts to expand as they heat; wrong clearance causes noise or valve damage.

A test instrument that measures voltage, resistance and current, used to trace circuits, check continuity and confirm that power is delivered and returned correctly.

An engine-driven generator that produces alternating current, rectifies it to direct current, and charges the battery while powering the vehicle's electrical loads.

A measurement of voltage lost across a cable or connection while current flows; excess drop points to corrosion, loose terminals or undersized wiring.

A digital data bus that lets electronic control units share sensor readings, commands and fault information over a twisted pair, replacing large bundles of individual wires.

An alphanumeric code stored by an electronic control module when it detects an abnormal or out-of-range signal, giving the technician a starting point for diagnosis.

An engine-driven pump that builds and maintains air pressure in the vehicle's reservoirs for the brakes and other air-operated systems.

A unit downstream of the compressor that removes water and oil from compressed air and periodically purges them, protecting valves from corrosion and ice.

A valve on the air compressor that cuts the compressor in at a low reservoir pressure and out at a high pressure, keeping system pressure within the manufacturer's range.

A valve that uses a small control signal to quickly supply or exhaust a large volume of air to the brake chambers, speeding up brake application and release.

The lever on the brake camshaft that turns pushrod travel from the chamber into camshaft rotation, and is adjusted to compensate for lining wear.

A canister with a diaphragm that turns air pressure into pushrod force, applying the foundation brake when air is admitted.

A chamber containing a strong coil spring that applies the parking brake when air pressure is released, and is held off by air while the vehicle is driven.

A pump that converts pedal force into hydraulic pressure and sends fluid to the wheel brakes, with a reservoir and ports that allow for fluid expansion.

A hygroscopic hydraulic fluid that carries pressure from the master cylinder to the wheel brakes; it absorbs moisture over time and must meet the specified DOT rating.

A temporary loss of braking power when friction linings or fluid overheat, common after repeated hard stops; braking recovers as the components cool.

The vertical steel pin that joins the steering knuckle to the axle and forms the pivot axis the front wheel steers around.

The forward or rearward tilt of the steering axis; positive caster helps the wheels self-centre and improves straight-line stability.

The difference between the front and rear measurements taken across a pair of tyres; wrong toe scrubs the tyres and can offset the steering wheel.

The specified distance between the frame and the axle, set by air springs or suspension geometry; correct height keeps alignment and driveline angles in specification.

A friction assembly that connects and disconnects the engine from the transmission so the vehicle can pull away from rest and change gears.

A cross-and-bearing coupling that lets a driveshaft carry torque through changing angles as the axle moves with the suspension.

A gear set that divides torque between the two drive wheels while letting them turn at different speeds in a turn.

The alignment of the universal joint yokes on a two-piece shaft so their working angles cancel; wrong phasing produces vibration and component wear.

The fluid in an air conditioning system that absorbs heat as it evaporates in the evaporator and releases it as it condenses in the condenser.

A tank that stores liquid refrigerant and holds desiccant to remove moisture and a filter to catch debris before the refrigerant reaches the expansion device.

A metering device that controls refrigerant flow into the evaporator and drops its pressure so it boils and absorbs heat from the cab air.

The horseshoe-shaped coupling mounted on the tractor that locks onto the trailer kingpin, carrying vertical load and letting the trailer pivot.

A rubber or air cushion between the cab and the frame that isolates the driver from vibration and allows slight movement as the frame flexes.

A computer-controlled nozzle that atomizes fuel and delivers it into the combustion chamber at the exact time and quantity the engine control module commands.

An exhaust component that traps soot particles; it is cleaned by regeneration, which burns the collected soot at high temperature.

A urea-and-water solution injected into the exhaust ahead of the SCR catalyst to turn nitrogen oxides into nitrogen and water; it is stored in its own tank.

An aftertreatment system that injects diesel exhaust fluid over a catalyst to convert nitrogen oxides in the exhaust into nitrogen and water.

A valve that meters exhaust gas back into the intake to lower combustion temperature and reduce the formation of nitrogen oxides.