Forensic Investigation of a Tractor Fifth-Wheel Failure

Failed Fifth Wheel Investigation
Failed Fifth Wheel Investigation
Image of Worn Jaw on 5th Wheel
Image Showing Wear on Kingpin Neck

Forensic Investigation on a Tractor Trailer Fifth-Wheel Failure which involved an Accident due to Separation of the Trailer from its Tractor.

Shown above center is the excessive wear on the ID of the Jaw in contact with the neck of the Kingpin. At the top edge, extruded metal can be seen due to repeated impact. We concluded that it was not possible for the 5th wheel’s jaw to become unhooked while travelling if it was properly hooked up and locked in place initially. Therefore, the jaw had to be only partially hooked up. The excessively thick and dirty grease interfered, and did not allow the jaw to be fully inserted into the lock. 

The partially hooked jaw can become unhooked due to a number of reasons such as:

  • Excessive vibrations due to imbalanced and improperly tied down load
  • Worn out and out of tolerance kingpin and jaw
  • Traveling on winding road, and
  • Carrying heavier load than permitted.

A Fifth Wheel is a crucial component of a semi-truck’s tractor that connects the tractor and the trailer, allowing both to articulate, and steer. It is a flat, non-rotating horseshoe-shaped coupling device installed on the semi-truck tractor, where the trailer’s kingpin engages. The kingpin on the trailer installs into the fifth wheel on the tractor, and the two components rotate against each other with the help of grease to reduce friction. The fifth wheel is designed to spread the trailer’s freight load evenly across the tractor and trailer, enabling safe hauling.


O’Donnell Consulting Performs Forensic / Expert Witness Services on Tractor Trailor / Trucking Accidents. 

We Support Law Firms and Major Insurance Companies in State & Federal Courts – from Simple to Complex issues. As an Independent Forensic Engineering Firm, we Provide Unbiased, Comprehensive Technical Results.

(412) 835-5007

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