CDL Combination Vehicles

Before backing a tractor under a trailer, where should the trailer be positioned relative to the fifth wheel?

1. ABelow the frame rails so the kingpin drops in freely
2. BAt the exact same height so no lifting occurs
3. CLow enough that the trailer is raised slightly by the tractor as you back under itCorrect
4. DSlightly higher than the fifth wheel so it can slide up as you back

Why: The trailer should be low enough that it is raised slightly when the tractor backs under it. This ensures the fifth wheel makes solid contact and the kingpin seats properly. If the trailer is too low the tractor may hit and damage the nose; too high and it can miss the fifth wheel.

When inspecting the coupling system of a combination vehicle, what should you check about the fifth wheel mounting?

1. AThat it is painted to match the cab
2. BThat mounting bolts and brackets are secure and none are missing or brokenCorrect
3. CThat it is tilted forward
4. DThat the fifth wheel is completely dry

Why: During inspection you must check that the fifth wheel is securely mounted, with no missing or broken mounting bolts, brackets, or welds. A loose or cracked fifth wheel mount can fail under load. This is a critical part of the combination vehicle coupling inspection.