FL CDL Doubles/Triples flashcards

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

Converter dolly

A short, two- or three-axle frame with a fifth wheel and a kingpin plate that connects a lead trailer's rear kingpin to a following trailer's kingpin, allowing doubles and triples to pivot independently.

Upper coupler plate

The flat, reinforced plate on the front of a converter dolly that contacts the lead trailer's rear fifth wheel; it must be inspected for cracks and wear at every coupling.

Tug test

After coupling, apply the trailer brakes and pull gently forward against them; if the fifth wheel is properly locked, the trailer holds and the tractor does not separate from it.

High hitch

A condition where the fifth wheel jaws close over the top of the kingpin head instead of around its shank; the coupling looks closed but the trailer can separate under load.

Uncoupling order

Chock all wheels, release the dolly from the lead trailer, then release the lead trailer from the tractor; reversing the coupling sequence prevents the combination from rolling or folding.

Dolly air lines

The emergency (red) and service (blue) lines connect the dolly to the lead trailer; the emergency line charges the dolly tank and releases its spring brakes, while the service line carries brake signals.

Dolly landing gear

Retractable legs on the converter dolly that support it when uncoupled; they must be fully raised and the crank secured before the combination moves, or they can drag on the road.

Dolly safety chains

Chains that attach the converter dolly to the lead trailer or dolly frame as a backup connection; they must be attached, untwisted, and not dragging during the walk-around inspection.

Gladhand seals

Rubber O-rings inside the air line couplers; cracked or missing seals leak emergency line pressure, which can set the trailer spring brakes and disable the combination.

Pushrod travel

The distance a brake chamber pushrod extends when the brakes are applied; excessive travel on any trailer or dolly brake means the brakes are out of adjustment.

Dolly frame cracks

Cracks that develop at the upper coupler plate and fifth wheel mounting under repeated coupling loads; they must be found during inspection because a cracked dolly can fail in service.

Kingpin inspection

Check each trailer kingpin for wear, gouges, and a bent flange; a damaged kingpin will not lock securely in the fifth wheel jaws and can allow separation.

Walk-around sequence

Start at the tractor front, work down the driver side, cross to the passenger side, check each trailer rear, and inspect the dolly from both sides and underneath.

Trailer ABS cord

The electrical cord and plug that power the dolly's ABS and marker lights; chafed insulation or corroded pins cause lighting and ABS faults that must be corrected before driving.

Off-tracking

The difference between the path of the tractor's front wheels and the path of the rear trailer's wheels; it increases with each added trailer, so doubles and triples cut corners more sharply.

Rearward amplification

The tendency of the last trailer in a multi-trailer set to swing wider than the tractor during a rapid maneuver; it grows with speed and with the number of trailers.

Crack-the-whip effect

A sway that starts at the tractor and grows toward the rear trailer, magnified by speed and trailer count; the last trailer can swing into an adjacent lane or off the road.

Backing a multi-trailer set

Only the rearmost trailer responds predictably to steering; it moves opposite the steering wheel direction, so back slowly with a spotter and small corrections.

Turn pivot points

Each trailer pivots at its own kingpin, so a doubles or triples set sweeps a wider path than a single; watch the dolly and rear trailer in the mirrors through every turn.

Mirror setup for doubles

Mirrors must be adjusted so the dolly wheels and the side of the rear trailer are visible; without that view you cannot monitor off-tracking or clearance in turns.

Low-speed cornering

In tight, low-speed turns the rear trailer cuts the corner most severely, so swing wide and check the mirror for the dolly and rear trailer before completing the turn.

Emergency (red) line

The air line that charges trailer tanks and releases spring brakes; losing emergency line pressure automatically applies the spring brakes on all trailers in the combination.

Service (blue) line

The air line that carries the brake application signal; if it breaks, the trailers will not brake when the treadle is applied even though the emergency line still holds pressure.

Trailer hand valve

The trolley valve applies only the trailer brakes; it is for testing trailer brakes and must never be used for parking or for normal stopping because it can cause a jackknife.

Progressive braking

Smooth, steadily increasing brake pressure on a multi-trailer combination; a hard, sudden application lets the rear trailers push the tractor and can fold the combination.

Brake fade on grades

Overheated drums lose braking force during continuous service brake use on a long downgrade; select a low gear before the descent and use engine braking instead.

Following distance rule

Allow at least one second per ten feet of vehicle length plus one second for speed; a longer combination needs more room because total weight increases stopping distance.

Crosswind effect

A gust pushes the last trailer sideways and can start a sway that amplifies forward through the combination; slow down and grip the wheel firmly in windy conditions.

Speed and amplification

Rearward amplification grows with speed, so slowing down before a lane change or curve is the most effective way to keep the last trailer in its lane.

Sway recovery

If the combination starts to sway, release the accelerator and steer straight; hard braking transfers weight forward and worsens the sway rather than correcting it.

Railroad crossing check

Stop and confirm the dolly landing gear is fully raised and no part of the combination will drag on the rails before crossing; a dragging dolly can derail or be struck.

Passing clearance

The rear trailer is the last unit to clear a passed vehicle; do not return to the lane until the entire combination, including the last trailer, has cleared it.