Kentucky CDL Combination flashcards

32 cards. Read the term and the definition here. The deck at the top of this page is optional.

Offtracking

The difference between the path followed by the front wheels and the path followed by the rear wheels of a combination vehicle. It increases with wheelbase and with sharper turns.

Rearward amplification

The tendency of the last trailer in a multi-trailer combination to swing wider and faster than the tractor during a lane change or turn, increasing rollover risk.

Tractor protection valve

A valve that closes automatically when trailer air pressure drops to roughly 20 to 45 psi, sealing the tractor air supply and applying the trailer spring brakes.

Low-air warning

A buzzer and light that must activate before air pressure drops below 60 psi, warning the driver that spring brakes will soon apply.

Static leak test

With the engine off and full pressure, hold the brakes and watch the gauge; loss should not exceed about 3 psi per minute for a single vehicle or 4 psi for a combination.

Trailer ABS lamp

An amber lamp on the trailer's left rear or the dash that stays on when the trailer's antilock system is disabled; normal trailer brakes remain but without antilock protection.

ABS braking technique

During an antilock event, hold steady pressure on the brake pedal and steer; do not pump the brakes, because pumping defeats the system's pressure modulation.

ABS startup check

The ABS lamp should come on at startup and go out after a few seconds; if it stays on, the system has logged a fault and should be checked.

Kingpin

The pin on the trailer that locks into the tractor's fifth-wheel jaws; it must be inspected for damage and confirmed locked before moving.

Tug test

After coupling, pull forward gently with the trailer brakes set to confirm the fifth-wheel jaws are locked around the kingpin before releasing the brakes.

Uncoupling order

Set the trailer brakes, lower the landing gear, disconnect the electrical cable and glad hands, pull the fifth-wheel release, then pull forward slowly.

Slack adjuster check

With the brakes released, pull the slack adjuster by hand; more than about one inch of movement at the push rod indicates adjustment is needed.

Tire tread minimum

At least 4/32 inch on front tires and 2/32 inch on other tires; also check for cuts, bulges, and mismatched duals.

Converter dolly

A device with its own axle, wheels, brakes, and fifth wheel that carries the front of the rear trailer in a double or triple combination.

Dolly air supply

The dolly's air lines must be connected to the rear trailer and to the tractor supply; a dolly with no air supply has no working brakes.

Doubles endorsement

A special endorsement required to tow double or triple trailers; such combinations are prohibited on many routes, so check the approved network.

Trailer swing correction

If the trailer starts to push the tractor, release the brake pedal briefly to let the wheels roll and regain traction, then reapply.

Drive-wheel skid

Corrected by releasing the brakes and steering in the direction of the skid; a locked drive axle can cause a jackknife before ABS intervenes.

Stopping distance and speed

Stopping distance increases with the square of speed; doubling speed roughly quadruples the distance needed to stop.

Engine brake use

On long downgrades, select a gear low enough that the engine brake and service brakes together hold the speed; do not ride the brakes.

Right-turn technique

Swing wide to the left before turning, then bring the tractor close to the right curb as the trailer follows; watch the trailer's right rear wheels.

Backing with a spotter

Use a spotter and get out and look; back toward the driver's side when possible and keep the trailer's rear in view.

GOAL

Get out and look; a backing procedure used when visibility is limited or the path is unclear, before moving the vehicle.

Center of gravity

The point where the vehicle's weight is concentrated; it rises with load height and lowers the speed at which a rollover can occur in a turn.

Rollover threshold

The lateral force in a turn exceeds the vehicle's stability limit; the critical speed decreases as the center of gravity rises and the turn tightens.

Load placement

Load the heaviest cargo low and centered over the axles; an off-center or top-heavy load increases rollover risk and the chance of a load shift.

Tiedown requirement

The aggregate working load limit of tiedowns must be at least half the cargo weight, and the number of tiedowns depends on cargo length and weight.

Glad hands

Couplers that connect the tractor's air lines to the trailer's; the emergency supply line and the service line must not be crossed.

Fifth-wheel jaws

The locking mechanism that grips the trailer kingpin; the jaws must be closed around the pin and the safety latch engaged before moving.

Landing gear

The trailer's support legs; they must be fully raised and the crank handle secured before moving, and they are not designed to hold a loaded trailer on a slope.

Trailer hand valve

A control used only to test trailer brakes before a trip; using it to stop a moving combination can cause the trailer to swing out.

Trailer sway response

If sway starts, ease off the accelerator and avoid hard steering or braking; a high, heavy load increases the tendency to sway.