CDL Doubles/Triples cheat sheet

A converter dolly is a separate frame with its own fifth wheel and a drawbar; it attaches to the rear of a lead trailer so that trailer can pull a second trailer.

The dolly drawbar eye hooks to a pintle hook on the rear of the lead trailer; the pintle latch must be closed with its safety pin or cotter installed.

Two safety chains connect the dolly to the lead trailer and must be crossed under the drawbar so they cradle it if the pintle hook fails.

The dolly carries its own service and emergency air lines plus an electrical cable; these connect to the lead trailer's rear couplers.

Shut-off valves at the rear of any trailer that supplies air to a following unit must be OPEN; shut-off valves at the rear of the last trailer must be CLOSED.

Converter dollies built on or after March 1, 1998 must be equipped with spring brakes; older dollies may have no brakes at all.

Standard glad hand color code: blue is the service line (applies trailer brakes), red is the emergency/supply line (charges trailer tanks and sets spring brakes on separation).

Never use the trailer hand valve (spike) while driving; it applies only the trailer brakes and can cause a jackknife.

Each trailer added increases combination length, off-tracking, swept width, and the rearward swing of the last trailer.

Before coupling, verify the fifth wheel jaws are open and greased, the mounting is secure, and the trailer kingpin is undamaged.

Set the trailer height so the tractor will lift it slightly when backing under; too low and the kingpin strikes the fifth wheel, too high and the jaws may not lock.

Back under slowly in a straight line and stop when the fifth wheel contacts the trailer apron.

Tug test: after the jaws close, pull forward gently twice; if the trailer moves with the tractor, the coupling is locked.

After coupling, connect blue to blue and red to red, charge the trailer air system, shut off the engine, and listen for leaks before moving.

Raise the landing gear fully after coupling and secure the crank handle so it cannot swing out.

Uncoupling order: set the trailer spring brakes (or chock the wheels), lower the landing gear to firm ground, disconnect the air lines and electrical cord, then pull the fifth wheel release handle.

Close the shut-off valves and cap or secure the glad hands when uncoupling to keep out dirt and moisture.

Never pull the fifth wheel release handle while weight is still resting on the fifth wheel; the tractor can jump when the kingpin releases.

Check the pintle hook: latch closed, safety pin or cotter in place, no excessive wear on the hook or drawbar eye.

Check both dolly safety chains: attached, crossed under the drawbar, not kinked, twisted, or worn.

Check every glad hand and electrical connection: seals present, couplers fully seated, no chafing, and service/emergency lines not crossed.

Check shut-off valves: open at the rear of trailers that supply air, closed at the rear of the last trailer.

Check each fifth wheel (tractor and dolly): jaws closed, locking lever secured, no gap between the trailer apron and the fifth wheel.

Check tires, wheels, lug nuts, brakes, lights, and mud flaps on the tractor, every trailer, and the dolly.

Confirm the dolly's spring brakes are released when air is charged and will apply automatically if air pressure is lost.

Inspect the rear of the last trailer for working lights, secured air lines and cord, closed shut-off valves, and an undamaged rear bumper or ICC bar.

Static leak test: engine off, brakes released, air loss must not exceed 3 psi per minute for a single vehicle or 4 psi per minute for a combination.

Applied leak test: hold the brake pedal down with the engine off; loss must not exceed 3 psi per minute (single) or 4 psi per minute (combination).

The low air pressure warning (buzzer or light) must activate before pressure falls below 60 psi.

The tractor protection valve closes the tractor's air supply to the trailer at roughly 20-45 psi, protecting the tractor's brakes.

The trailer air supply knob charges the trailer emergency line when pushed in and applies the trailer spring brakes when pulled out.

If the service and emergency lines are crossed, trailer brakes may fail to release or may drag; always match blue to blue and red to red.

Test trailer spring brakes by pulling the trailer air supply knob out and gently tugging; the trailer must not move.

Build pressure to governor cut-out (about 120-140 psi) and confirm the compressor cuts out and later cuts back in at the correct pressure.

Drain the air tanks daily and check the discharge for water or oil, which indicate moisture or compressor problems.

Off-tracking: the rear wheels of the last trailer track inside the tractor's path, so turns must be made wider to keep them off curbs and out of adjacent lanes.

Crack-the-whip: the rear trailer swings outward during turns and stops; drive slowly and watch the last trailer's rear in the mirrors.

Avoid backing doubles/triples; if backing is unavoidable, back only in a straight line, at low speed, with a spotter.

Following distance rule: below 40 mph, allow one second per 10 feet of vehicle length plus one extra second; add more time for doubles/triples and bad weather.

Brake early and smoothly; hard braking can swing the rear trailer out or trigger a jackknife.

Reduce speed in curves, on ramps, and in crosswinds; multi-trailer combinations have a high center of gravity and sway easily.

Crosswinds affect the rear trailer most; slow down and make gentle, small steering corrections.

Never use the hand valve while driving; it applies only the trailer brakes and can cause a jackknife.

At railroad crossings, stop, look, and listen, and make sure the entire combination can clear the tracks before starting across.