Investigation of Truck Brake Failure

A medium duty truck was turning into a construction zone along a curve from one highway to another.  Suddenly, the left front brake locked causing a sharp left turn. The truck impacted with concrete construction barriers.  Six weeks prior, the truck had a complete brake overhaul. Visual and microscopic examination of the left front brake shoes and other debris contained within the truck wheel and brake drum revealed a loose and highly deformed castellated nut and washer.  The brake shoes were visibly damaged and the castellated nut exhibited imbedded brake lining material. Photograph A shows an overall view of the subject brake lining.

Photograph A  Brake shoe from left front wheel
 of subject truck.  Note gouged and eroded
 surface of new brake shoe.

This failure and accident resulted from improper installation of the castellated nut during brake shoe replacement and brake overhaul. The brake lining imbedded castellated nut is shown in Photograph B.

Photograph B  Deformed castellated nut from
 brake shoe assembly showing embedded
 brake lining material.

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