The subject vehicles range in age from 4?7 years in service, with average mileages estimated to range from 50 to 100 thousand miles.at these mileages, the subject wheels are likely to have been removed and reinstalled multiple times for various service procedures.ODI is concerned about the high wheel separation rates in the MY 1997-98 Windstar vehicles equipped with aluminum alloy wheels.however, analysis of failure data indicates that most of the incidents in that population of vehicles occur after the vehicles had accumulated 30 thousand miles of service. The factors that increase the risk that inadequate clamp loads may be achieved during service-related wheel installation are not unique to the subject vehicles.testing conducted by Ford and VRTC indicate that the MY 1998 Windstar aluminum wheel fastening system performs similar to the wheel fastening systems on peer minivans.no design or manufacturing defects were identified in the wheel fastening systems of the subject vehicles. Ford will send a mailing to owners of Windstar vehicles with aluminum wheels that have high wheel separation rates that reviews the appropriate wheel fastening procedures and states that the wheel nuts should be tightened to the nominal torque, 100 ft-lbs (136 nm), and re-tightened to the same torque after 500 miles.Ford"S letter also states that it is ?a good practice to be sure that before installing the wheel the aluminum wheel mounting surface, wheel lug nut area, and the mounting flange are free from dirt, debris, and loose rust to ensure the wheel is seated correctly and the wheel lug nuts remain fully tightened." ODI will continue to monitor the incidence of wheel fastener failures in the subject vehicle population.accordingly, this investigation is closed.the closing of this investigation does not constitute a finding by NHTSA that a safety-related defect does not exist.the Agency will take further action if warranted by the circumstances. For additional information, see the attached closing report.
