AK CDL Combination flashcards

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

Fifth wheel

A horseshoe-shaped steel plate mounted on the tractor that locks around the trailer's kingpin to connect the tractor and trailer.

Kingpin

A vertical steel pin mounted under the trailer's nose that locks into the tractor's fifth wheel jaws to hold the trailer.

Service air line

The blue-coded air line that carries the driver's brake-application pressure from the tractor to the trailer's brake system.

Emergency air line

The red-coded air line that supplies air to the trailer; if it loses pressure, the trailer's spring brakes apply automatically.

Glad hands

Couplers with rubber seals that connect the tractor and trailer air lines; damaged seals cause pressure leaks and weak trailer braking.

Landing gear

The retractable support legs under the trailer nose that hold an uncoupled trailer level and must be fully raised before towing.

Pull test

After coupling, with trailer brakes set, gently pull forward in low gear to confirm the kingpin is locked and the tractor cannot separate.

Coupling sequence

Set trailer brakes, back squarely under the trailer, raise the fifth wheel to contact the apron, then push until the kingpin locks.

Uncoupling sequence

Set trailer brakes, lower landing gear, chock wheels if needed, disconnect lines and cord, then release the fifth wheel.

Connect lines order

Connect the emergency (red) line first, then the service (blue) line, then the electrical cord; disconnect in reverse order.

Trailer brake auto-set

Trailer spring brakes apply automatically when air pressure is lost; a trailer with no air supply cannot be moved safely.

Fully raised landing gear

Landing gear must be cranked fully up before towing so no part of the gear extends below the trailer frame.

Pre-trip coupling check

Confirm fifth wheel jaws are locked, release handle secured, kingpin seated, and no gap between tractor frame and trailer nose.

Trailer light check

Verify running lights, left and right turn signals, four-way flashers, brake lights, and clearance marker lights all function before driving.

Rear impact guard

The underride guard at the rear of the trailer that must be present and secure during a pre-trip inspection.

Static leak test

With full pressure and engine off, release the parking brake and confirm pressure loss does not exceed 3 psi per minute on a single unit.

Combination leak rate

For a combination vehicle with parking brake released, static air pressure loss should not exceed 4 psi per minute.

Low-air warning

The warning buzzer or light must activate before air pressure drops below 60 psi.

Spring brake set point

With pressure fanning off, the tractor and trailer spring brakes should set automatically around 40 to 45 psi.

Compressor build time

The air system should build from 85 to 100 psi in about 45 seconds at operating RPM.

Governor cut-out

The pressure at which the compressor stops building, typically near 120 to 125 psi; cut-in is near 100 psi.

Off-tracking

The difference between the path of the tractor's front wheels and the trailer's rear wheels; it increases with sharper turns and longer wheelbases.

Rearward amplification

The tendency of the last trailer in a multi-trailer combination to swing wider than the tractor during a sudden maneuver.

Trailer sway

Fishtailing of the trailer, amplified when it is lightly loaded or the cargo is concentrated at the rear.

Sway correction

Ease off the throttle gradually, hold the steering steady, and avoid abrupt brake or steering inputs to stop trailer sway.

Load placement

Place the heaviest cargo over or ahead of the trailer axles to reduce sway and improve stability.

Wide right turn

A combination needs a wider turn because the trailer's rear wheels track inside the tractor's path; watch the trailer's right mirror.

Jackknife correction

If the trailer begins to jackknife, release the brakes and steer to pull the tractor and trailer back into line.

Stab braking

On slippery surfaces, apply the brakes firmly to set them, release if wheels lock, and reapply to maintain control.

Downgrade braking

Select a low gear so engine braking controls speed without continuous service brake use that can overheat and fade.

High wind handling

Reduce speed and grip the wheel firmly; empty or lightly loaded trailers are most vulnerable to being blown over.

Escape ramp use

If brakes fail on a downgrade, aim for the gravel arrester bed and keep the vehicle straight to stop safely.