NHTSA Preliminary Evaluation PE23004

On March 17, 2023, the Office of Defects Investigation (ODI) opened PE23-004 to investigate instances of drag link separation in model year (MY) 2016-2020 Vision school buses manufactured by Blue Bird Body Company (Blue Bird). Since drag links are serviceable items that can wear out, ODI opened this investigation to understand why two drag links separated at the steering arm end shortly after having passed a routine inspection by multiple qualified entities.Two buses used in the same rural school district, owned and maintained by different bus contractors, had both undergone similar annual and semi-annual inspections prior to the start of the school year.Both failed within a week of each other, approximately a month into the school year. ODI interviewed the bus contractors and surveyed the industry to learn what inspection methods were being used and which ones were best at detecting wear in the components.ODI learned that the failed buses had not been inspected using the most thorough methods. ODI collected the drag links from each of the failed buses. Assisted by the Pennsylvania State Police Motor Carrier Enforcement Division and using best practice inspection methods, ODI identified and collected a pre-separation drag link from a neighboring school district.  The drag links underwent a teardown inspection at the Vehicle Research and Test Center (VRTC) jointly with Blue Bird and THK-Rhythm Automotive, the drag link manufacturer.In all cases, the visual analysis of each drag link end revealed that the grease at the steering arm end was dirty, discolored, and dry in texture, while the pitman arm end was still clean looking and fluid. ODI reviewed the information request data submitted by Blue Bird.No other separations had been reported.ODI contacted additional fleets to determine whether any other separations had occurred that had not been included in the submitted warranty and claim data.None were found. The grease fitting on the steering arm end is obscured by th