CDL Doubles/Triples study guide
CDL Doubles/Triples · Work through your exam, one topic at a time.
The Doubles/Triples (T) endorsement is added to a Commercial Driver's License to authorize operating a combination of two or three trailers - the configuration used by less-than-truckload carriers, package and parcel linehaul runs, and fuel or beverage operations that pull pup trailers. It is a knowledge endorsement, not a separate license: you must already hold (or be working toward) a CDL, and your state licensing agency determines what else it wants to see before the endorsement appears on your record. The CDL Doubles/Triples study guide has 5 sections and about 1,737 words.
01Pulling Double/Triple Trailers: Converter Dollies, Couplers, and Air Supply
A double or triple carries its extra trailers on converter dollies . A converter dolly is a small frame with a fifth wheel, one or two axles, and a drawbar ending in a pintle eye (lunette) that drops over the pintle hook on the rear of the trailer ahead.
364 words, about 2 min02Coupling and Uncoupling Doubles and Triples
Inspect the fifth wheel first: jaws open, plate greased, mounting bolts tight, kingpin and apron undamaged. Set the trailer spring brakes (or chock the wheels) and line up squarely.
351 words, about 2 min03Inspecting Doubles and Triples
Doubles and triples need everything a single trailer needs, plus an inspection of every coupling point and every converter dolly . Walk the whole combination in one direction so no joint is skipped.
339 words, about 2 min04Checking Air Brakes on a Double or Triple
Test the air system with the whole combination connected , because every extra glad hand, hose, and dolly is another place to leak. Build-up: with the engine at fast idle, pressure should rise from 85 to 100 psi within 45 seconds in a combination vehicle.
327 words, about 2 min05Driving Doubles and Triples
Every trailer's wheels track inside the path of the unit ahead - off-tracking. With two or three trailers the cut is cumulative, so the last trailer can be several feet inside your turn.
356 words, about 2 min