NJ CDL Combination key terms

The horseshoe-shaped coupling plate mounted on the tractor that locks around the trailer kingpin to hold the trailer attached while allowing it to pivot during turns.

The vertical steel pin under the front of the trailer that slides into the fifth wheel and is gripped by the locking jaws to connect trailer to tractor.

The spring-loaded metal claws inside the fifth wheel that close around the kingpin. A pull test confirms they are fully engaged before driving.

The flat plate under the trailer's front end surrounding the kingpin. It must rest flat on the fifth wheel so the coupling is solid and the trailer rides level.

After coupling, you pull forward gently with the trailer brakes set to confirm the kingpin is locked and will not slide out from under the tractor.

The retractable legs under the trailer front that support it when uncoupled. They must be fully raised before driving and firmly on the ground when parked.

The handle used to raise and lower landing gear. After use it must be secured in its stowed position so it cannot swing out and strike something.

The coupler fittings that join the tractor's air supply and service lines to the trailer's corresponding lines, sealed with rubber gaskets to prevent air leaks.

The air line that carries compressed air from the tractor to charge the trailer's reservoirs. It is also called the emergency line and applies trailer brakes if it separates.

The air line that carries the driver's brake application signal to the trailer relay valve. It is color-coded blue on most rigs.

A trailer valve that uses the small service-line signal to release a large volume of stored air quickly into the trailer brake chambers, speeding brake response.

A valve that closes automatically when trailer air lines separate or are disconnected, trapping tractor air so the tractor keeps braking ability and the trailer brakes apply.

A dash-mounted control, also called the trolley valve, that lets the driver apply only the trailer brakes independently of the tractor for testing and stability control.

Spring brakes on the trailer that set automatically when supply-line air pressure drops, such as during a breakaway, so the trailer stops on its own.

A situation where the trailer separates from the tractor. The supply line parts, pressure drops, and the trailer's spring brakes apply automatically to stop it.

Backup chains or cables that keep a trailer attached to the towing vehicle if the primary coupling fails, required on many towed combinations.

The engine-driven pump that builds and maintains air pressure in the vehicle's reservoirs. It must build pressure fast enough to keep up with brake use.

A device that controls the compressor, cutting it out at a set pressure and back in at a lower pressure to keep reservoir pressure within the proper operating range.

A unit that removes moisture from compressed air before it reaches the reservoirs, helping prevent freeze-ups and corrosion in valves and lines.

A tank that stores compressed air for braking. A combination vehicle has tractor tanks plus trailer tanks, and pressure must build and hold in all of them.

A light and buzzer that activate when reservoir pressure falls to a dangerous level, warning the driver to stop before automatic spring brakes engage.

Brakes held off by air pressure and applied by heavy springs when pressure is lost or the parking control is set. They also serve as the emergency brake system.

A check with the engine off and brakes released to confirm air pressure holds steady and does not drop faster than the allowed rate from leaks.

A check made with the brakes fully applied and held to confirm pressure loss stays within limits, verifying that brake chambers and lines are not leaking.

The cylinder where air pressure pushes a piston or diaphragm to apply the brake. Each wheel end typically has one, and a leak here weakens braking.

The linkage that transfers brake chamber pushrod force to the brake shoe. Too much pushrod travel means brakes are out of adjustment and stopping power is reduced.

How far the brake chamber pushrod extends when the brake is applied. Excess travel signals worn linings or misadjustment and must be corrected before driving.

Setting the slack adjusters so pushrod travel stays within limits. On combination vehicles, out-of-adjustment brakes cause uneven stopping and longer stopping distance.

The procedure of backing the tractor under the trailer, engaging the kingpin, connecting air lines, raising landing gear, and testing the connection before driving.

The procedure of parking on firm level ground, setting brakes, lowering landing gear, disconnecting air lines, and releasing the fifth wheel to separate tractor and trailer.

Wedges placed against trailer wheels when parking uncoupled so the trailer cannot roll. They are required whenever a trailer is left standing alone.

The tendency of a trailer's rear wheels to follow a tighter path than the tractor's front wheels in a turn, so the rear swings inside and can strike curbs or objects.

The total width of road a combination vehicle occupies through a turn, including the trailer's inside cut and the tractor's outside swing. It is wider than the vehicle itself.

Turning wide and slow, swinging left before the turn and checking mirrors throughout so the trailer's rear wheels clear the curb and nearby traffic.

Frequent scanning of both flat and convex mirrors to monitor trailer position, blind spots, and clearance while turning, changing lanes, or backing.

Areas beside and behind a combination vehicle that mirrors do not show. A driver must know these zones and avoid moving into them or lingering there.

The large areas around a big rig where other drivers cannot see the truck's mirrors or be seen by the truck driver, requiring extra caution when sharing the road.

The gap kept behind the vehicle ahead, measured in seconds. A loaded combination needs at least one second per ten feet of vehicle length plus extra for speed and conditions.

The total distance traveled from perception to full stop, combining reaction distance and braking distance. It grows with weight, speed, and poor road conditions.

The delay between pressing the pedal and air pressure reaching the brakes, roughly a fraction of a second, which adds distance at highway speed.

Choosing a safe speed based on weight, grade, curves, weather, and traffic rather than the posted limit, since a loaded rig needs far more room to slow.

Selecting a lower gear before a downgrade or curve so engine braking helps control speed and the brakes are not overheated from continuous use.

A retarding device that uses engine compression to slow the vehicle without wheel brakes, helping preserve brake capacity on long descents.

Loss of braking power from overheated drums and linings after repeated or prolonged use, common on long downgrades when speed is controlled by brakes alone.

A skid where the tractor and trailer fold toward each other at the coupling, often caused by locking the drive wheels or braking hard on a slippery surface.

A skid where the trailer's rear wheels lose traction and the trailer swings sideways out of line with the tractor, usually from overbraking or sudden steering.

Loss of tire grip so the wheels slide rather than roll, removing steering and braking control until traction is recovered by releasing the brake or easing off.

An antilock braking system that rapidly releases and reapplies brake pressure to prevent wheel lockup, helping the driver keep steering control during hard stops.

The grip between tires and road surface. Rain, ice, gravel, and worn tread reduce it, so a combination vehicle needs lower speed and gentler inputs in those conditions.

Riding on a film of water so tires lose contact with the pavement, causing sudden loss of steering and braking. Easing off the throttle helps tires regain grip.

The buffer of clear space kept around the vehicle on all sides so there is room to react, stop, or steer away from a developing hazard.

Moving to another lane only after signaling, checking mirrors and blind spots, and confirming the trailer has cleared the lane before completing the move.

The arc a combination vehicle follows in a turn. It is much larger than a car's, so wide turns and advance planning are needed to avoid curbs and poles.