CDL Doubles/Triples flashcards
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32 cards. Read the term and the definition here. The deck at the top of this page is optional.
- Converter dolly
- A separate frame with its own fifth wheel and drawbar that couples to the rear of a lead trailer so that trailer can pull a second trailer.
- Pintle hook
- The coupling on the rear of a lead trailer that the converter dolly's drawbar eye attaches to; its latch must be closed with the safety pin in.
- Dolly safety chains
- Two chains connecting the converter dolly to the lead trailer; they must be crossed under the drawbar to catch the dolly if the pintle hook fails.
- Shut-off valves
- Valves at the rear of a trailer that control air flow to a following unit; open on trailers that supply air, closed at the rear of the last trailer.
- Blue glad hand
- The coupler for the service air line; it carries the air pressure that applies the trailer brakes when the brake pedal is pressed.
- Red glad hand
- The coupler for the emergency or supply line; it charges the trailer air tanks and applies the trailer spring brakes if the line separates.
- Dolly spring brakes
- Converter dollies built on or after March 1, 1998 must have spring brakes that apply automatically whenever air pressure is lost.
- Tug test
- After coupling, pull forward gently twice against the trailer; if the trailer moves with the tractor, the fifth wheel jaws are locked.
- Fifth wheel jaws
- The locking mechanism that grips the trailer kingpin; check that they are open before coupling and fully closed after.
- Trailer kingpin
- The vertical pin under the trailer nose that locks into the fifth wheel; inspect it for damage, wear, and a missing or loose mounting.
- Landing gear
- The support legs under the trailer nose; raise them fully after coupling and lower them to firm ground before uncoupling.
- Fifth wheel release handle
- The lever that opens the fifth wheel jaws to release the kingpin; pull it only after the landing gear is down and air lines are off.
- Fifth wheel gap
- A visible space between the trailer apron and the fifth wheel after coupling; it means the kingpin is not locked and must be corrected.
- Coupling air leak check
- After connecting the lines, charge the trailer air system, shut off the engine, and listen for leaks before moving the vehicle.
- Fifth wheel inspection
- Check jaws closed, locking lever secured, no gap between apron and fifth wheel, mounting bolts tight, and the plate properly greased.
- Glad hand seals
- Rubber seals inside glad hands prevent air leaks; check that they are present, not cracked, and that the couplers are fully seated.
- Crossed air lines
- When the service and emergency lines are swapped between units; the trailer brakes may fail to release or may drag while driving.
- Dolly walk-around check
- Check the converter dolly's tires, wheels, lug nuts, lights, mud flaps, brakes, and spring brake condition during the pre-trip inspection.
- Last trailer rear check
- Inspect the rear of the final trailer for working lights, secured lines, closed shut-off valves, and an undamaged bumper or ICC bar.
- Pintle hook wear
- Excessive wear in the pintle hook or drawbar eye can let the dolly separate; check the latch, safety pin, and hook opening.
- Leak rate rule
- With the engine off and brakes released, air loss must not exceed 3 psi per minute for a single vehicle or 4 psi per minute for a combination.
- Low air warning
- A warning buzzer or light must activate before air pressure drops below 60 psi, giving the driver time to stop safely.
- Tractor protection valve
- A valve that closes the tractor's air supply to the trailer when pressure falls to about 20-45 psi, protecting the tractor's brakes.
- Trailer air supply knob
- The dash valve that charges or shuts off the trailer emergency line; pulling it out applies the trailer spring brakes.
- Applied leak test
- Hold the brake pedal down with the engine off; air loss must not exceed 3 psi per minute for a single or 4 psi per minute for a combination.
- Governor cut-out
- The pressure at which the compressor stops pumping, usually about 120-140 psi; confirm it cuts out and later cuts back in correctly.
- Off-tracking
- The tendency of the rear wheels of the last trailer to follow a path inside the tractor's path, so turns must be made wider.
- Crack-the-whip effect
- The outward swing of the rear trailer during turns and stops; it can strike nearby objects, so drive slowly and watch the mirrors.
- Following distance rule
- Below 40 mph, allow one second per 10 feet of vehicle length plus one second; add extra time for doubles/triples and bad weather.
- Backing doubles/triples
- Backing a multi-trailer combination is unstable; avoid it, and if necessary back only in a straight line with a spotter.
- Crosswind handling
- Crosswinds push the rear trailer most; slow down, make gentle steering corrections, and avoid sudden lane changes.
- Hand valve caution
- The trailer hand valve applies only the trailer brakes and can cause a jackknife; use it for testing only, never while driving.