Failed Fifth Wheel Investigation
Image of Worn Jaw on 5th Wheel

We performed a forensic investigation on a fifth-wheel failure which caused separation of a trailer from its tractor.

Shown above on the right 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.


O’Donnell Consulting performs Forensic/ Expert Witness Services on trucking accidents – including those involving 5th Wheels.

Give us a call to discuss your technical issues.

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Tom O’Donnell, PE
Links of Engineering Resources

(412) 835-5007

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