Arizona CDL Combination Vehicles flashcards

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

Tug test

After coupling, gently pull forward with the trailer brakes applied to confirm the fifth wheel jaws have locked around the kingpin and the trailer will not separate.

Fifth wheel jaws

The locking mechanism that grips the trailer kingpin. Jaws must be fully closed with the release handle latched before the combination is driven.

Landing gear

The trailer support legs. Lower them to firm ground and crank them down until they bear the trailer weight before uncoupling from the tractor.

Emergency air line

The supply line that releases the trailer spring brakes. Connect it first and disconnect it last so the trailer stays braked when the lines are off.

Slack adjuster check

With brakes released, pull the slack adjuster by hand. More than about one inch of movement at the clevis means the brakes need adjustment.

Off-tracking

The tendency of a combination vehicle's rear wheels to follow a path inside the front wheels. Longer wheelbases produce greater off-track, so turns must be swung wide.

Following distance rule

Allow at least one second per ten feet of vehicle length below 40 mph, plus one extra second above 40 mph, giving roughly seven seconds for a 60-foot rig.

Downgrade braking

Select a gear low enough to hold speed without brakes, use engine braking, and apply the brakes in short firm applications instead of continuous light pressure.

Right turn setup

Approach in the left portion of the lane, move right just before the turn, and watch the trailer's rear wheels in the mirror to avoid hitting the curb.

Backing a combination

Back toward the driver's side, use a helper when possible, and turn the steering wheel toward the side you want the trailer to move.

Governor cut-out

The pressure at which the compressor stops building air, typically about 120 to 125 psi. Cut-in pressure is usually around 100 psi.

Static leak test

With the engine off and full pressure, hold the service brake released and watch the gauge. Loss should not exceed 3 psi per minute for a combination.

Tractor protection valve

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

Spring brakes

Brakes held applied by mechanical springs and released by air pressure. They apply automatically when pressure falls below about 20 to 45 psi.

Trailer hand valve

A control used only to test trailer brakes. It is not a parking brake and must not be used to hold the vehicle on a grade.

Drive-wheel jackknife

A jackknife caused by locked drive wheels, which lets the tractor swing out of line with the trailer. Releasing the brake pedal restores rolling traction.

ABS braking technique

With anti-lock brakes, hold firm steady pressure on the pedal and do not pump the brakes. The system prevents wheel lock-up automatically.

Front-wheel skid

A skid in which the front wheels lose traction and the vehicle will not steer. Release the brake to let the wheels roll, then steer gently.

Hydroplaning

Loss of tire contact with the road on a wet surface. Reduce speed, avoid sudden braking or steering, and hold the wheel steady until traction returns.

Escape ramp

A graded ramp for vehicles that lose braking on a downgrade. Aim for it early, keep the wheel straight, and use it rather than risking a runaway.

Axle weight limits

Federal limits are 20,000 pounds on a single axle, 34,000 pounds on a tandem group, and 80,000 pounds gross vehicle weight without a permit.

Bridge formula

A formula that limits the weight carried on any group of axles based on the number of axles and the distance between the first and last axle.

Tiedown count rule

Use one tiedown for every ten feet of cargo length, with at least two tiedowns, and an aggregate working load of at least half the cargo weight.

Center of gravity

The point where the load's weight is concentrated. Keeping it low and over the drive axles improves stability and reduces rollover risk.

Cargo blocking

Placing structures in front of and behind the cargo to prevent forward movement during braking and rearward movement during acceleration.

Railroad crossing stop

Stop within 50 feet but not less than 15 feet from the nearest rail when carrying passengers or hazardous materials, or when the crossing requires a stop.

Crossing procedure

At a railroad crossing, turn off the radio, open the window, look and listen both ways, and do not shift gears while crossing the tracks.

Stalled on tracks

If the vehicle stalls on the tracks, get everyone out and away from the tracks, then call the railroad using the emergency number posted at the crossing.

Placarded load

A vehicle carrying hazardous materials that requires placards. The driver must stop at railroad crossings and keep shipping papers within reach.

Wet road speed

Reduce speed by at least one-third on wet roads and by half on snow-packed roads, using gentle steering and braking inputs to avoid skids.

Fog driving

Use low-beam headlights, reduce speed, and increase following distance. High beams reflect off fog and reduce visibility, so avoid them.

Warning devices

Place reflective triangles within ten minutes of a stop: ten feet behind and 100 feet ahead on a two-lane road, and both directions on a divided highway.