Washington — The National Highway Traffic Safety Administration said Tuesday it is closing an investigation into steering failures in 335,000 heavy duty Ford pickups without seeking a recall.
Last year, NHTSA opened an investigation into 336,667 Ford 2008 F-250 and F-350 Super Duty pickups after receiving five complaints of steering gear failure.
NHTSA has previously investigated steering gear sector shaft cracking in 1.3 million 1999-2001 Ford Super Duty pickups and 2000-01 Ford Excursion SUVs. That investigation, closed in 2003, didn't find any defects after reporting 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 2005 production, "increasing the resistance of the steering gear assembly to torsional overload by approximately 48 percent 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 pickup trucks."
NHTSA reviewed Ford's field return part analysis of failed steering gears from 2005 through 2009 Super Duty trucks that "found evidence of broken sector shaft gear teeth and piston damage consistent with incidents of single event overload."
But NHTSA "found no evidence of fatigue or material property defects in any of the fractures. Analysis of complaint rates by vehicle build month showed no patterns indicating potential manufacturing quality issues and no difference before and after Ford introduced design changes to the input shaft and sector shaft seals in July 2007 to address potential leak concerns."
NHTSA said the complaint rate in the 2008 trucks at 7.1 incidents per 100,000 is lower than the rate in the earlier investigation. NHTSA believes the "steering gear failure was most likely a result of crash forces, rather than the cause of the crash."