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CDL · Inspecting Combination Vehicles

When inspecting the coupling system on a combination vehicle, what is checked at the fifth wheel?

Reviewed by Jordan Morley, Editorial Lead at 247SimpleTests. Written by the 247SimpleTests Editorial Team from the official source material cited on every question.

Correct answer

Mounting bolts, locking jaws condition, release lever position, fifth wheel skid plate, kingpin engagement, and clearance

  1. A Only the grease level
  2. B Mounting bolts, locking jaws condition, release lever position, fifth wheel skid plate, kingpin engagement, and clearance
  3. C Only the air pressure to the locking mechanism
  4. D Only the visual appearance of the plate

Why this is the answer

The fifth wheel inspection covers: (1) Mounting — bolts tight, brackets not cracked or bent, mounting bracket plates intact; (2) Locking jaws — closed around the kingpin shank, not the kingpin head, no visible space between upper and lower fifth wheel; (3) Release arm — properly seated and safety latch in place; (4) Skid plate — adequately greased, no excessive wear; (5) Kingpin engagement — fully seated in the throat, no high hitch; (6) Clearance — adequate space between the tractor frame and the front of the trailer so they will not contact during turns. Defects in any of these can lead to trailer separation while driving, one of the most catastrophic possible failures.
Source: FMCSA CDL Manual 6.3 Inspecting the Coupling System

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About this topic: Inspecting Combination Vehicles

The combination-vehicle inspection adds fifth wheel, kingpin, glad hands, and trailer-specific items to the standard pre-trip routine. This is one of 13 Combination Vehicles questions on inspecting combination vehicles, each with a full explanation on a single study page.

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