NHTSA Preliminary Evaluation PE13014

The Office of DefectsInvestigation (ODI) opened PE13-014 after identifying five complaints alleging steering gear failure in model year (MY) 2008 Ford F-250 and F-350 Super Duty pick-up trucks and to evaluate the relationship between the design history of the steering gear assembly and the alleged defect.As background, ODI investigated steering gear sector shaft fractures in approximately 1.3 million MY 1999 - 2001 Ford Super Duty pick-up trucks and MY 2000 - 2001 Ford Excursion sport utility vehicles in Engineering Analysis EA01-009.The investigation determined that the sector shaft failures were the result of extraordinary, possibly multiple, impacts and not the result of fatigue.No defect in design, manufacturing or materials was identified in the sector shaft.EA01-009 was closed August 19, 2003 with 169 complaints, resulting in a rate of 12.9 incidents per 100,000 vehicles after approximately one year of service.Ford increased the diameter of the sector shaft from 1.375 inches to 1.625 inches at the start of MY 2005 production, increasing the resistance of the steering gear assembly to torsional overload by approximately 48% and changing the failure mode from sector shaft fracture to cracked or broken sector shaft gear teeth.The redesigned steering gear assembly was used in approximately 1.1 million MY 2005 through 2009 Ford Super Duty pick-up trucks, including the subject vehicles.Figure 1 shows the basic steering system design used in Ford Super Duty trucks investigated in EA01-009 and PE13-014. Figure 2 shows the locations of failures resulting from impact related torsional overloading of the sector shaft for the subject vehicles and the prior generation Ford Super Duty trucks investigated in EA01-009.Figure 3 shows an example of a failed sector shaft investigated in EA01-009 and comparisons of fracture surfaces of sector shafts failing from fatigue loading and from torsional overload.Ford provided field return part analysis of failed steering gears from MY 2