Truck and trailer parts glossary

Also called: tie rod end, track rod end, drag link

Steering linkage between the steering gear and the steered wheels: the tie rod (track rod) links the wheels to each other, the drag link joins the steering gear to the steering arm, and the rod ends are the ball joints at their ends.

Springs of one or more long, curved steel leaves that attach the axle to the frame, carry the load and soften road shocks.

Also called: U-bolt, leaf spring U-bolts

U-shaped bolts, threaded at both ends, that clamp a leaf spring to the axle.

Also called: shocks

Hydraulic dampers that slow the movement of the springs, keeping the wheels on the road and the vehicle or cab steady.

Bushes, mounts and buffers of rubber bonded to metal that join suspension, cab or engine parts and absorb vibration and small movements.

Also called: brake rotor

The wheel brake parts that turn with the wheel: shoes press against the inside of the drum, or pads clamp the disc, and the friction slows the wheel.

Also called: brake shoe

Curved metal shoes with a friction lining, pressed against the inside of the brake drum when braking.

Seals, boots, guide pins and adjuster parts to overhaul a disc brake caliper instead of replacing it.

Also called: spring brake chamber, air brake chamber, brake actuator

Actuators that turn compressed air into braking force. A spring brake chamber adds a strong spring that applies the brake for parking and in an emergency.

The shaft that spreads drum brake shoes: turned by the slack adjuster, its cam pushes the shoes against the drum.

Also called: automatic slack adjuster, brake adjuster

The lever that turns the push of the brake chamber into rotation of the brake camshaft. It also takes up the lining-to-drum clearance as linings wear; an automatic slack adjuster does this by itself.

Also called: truck air compressor

The engine-driven compressor that supplies compressed air to the brakes and other air systems of a truck.

Also called: relay valve, foot brake valve, air brake valve

Air system valves, such as relay and foot brake valves, that control, distribute and protect the air on its way to the brakes and other consumers.

Also called: trailer hub

The axle-end part that carries the wheel and the brake drum or disc and turns on the wheel bearings.

Also called: trailer legs, trailer landing legs

The pair of legs at the front of a semi-trailer, wound down to support it when uncoupled from the tractor unit.

Also called: fifth wheel, fifth wheel hitch

The coupling plate on a tractor unit that locks onto the semi-trailer kingpin and lets the trailer turn in corners.

Also called: suzie cable, trailer cable, 7-pin trailer plug

Cables, coiled leads, plugs and sockets that connect the trailer lights, brake electronics and other electrics to the truck.

Outer cab and body parts: bumpers, panels, steps, grilles and mudguards.

Mirrors, mirror heads and glasses that show the driver what is behind and beside the vehicle.

The hydraulic pump and cylinder that tilt the cab of a cab-over truck forward for access to the engine.

The heat exchanger at the front in which passing air cools the engine coolant.

The clutch between the engine and the cooling fan: it drives the fan when the engine needs cooling and lets it slow down otherwise.

The engine-driven pump that circulates coolant through the engine and radiator.

Belts that drive units such as the alternator, water pump, fan or air conditioning compressor from the crankshaft.

A tensioner keeps the drive belt tight; idler rollers guide it around the engine.

Threaded fasteners for wheels, suspension, brakes and body, such as wheel bolts, nuts and studs.