WHEEL STUD AND NUT

What NHTSA is examining

In december 1999, ford issued technical service bulletin 99-26-3, entitled increased wheel nut and stud size-service tip,for 2000 model year expedition, navigator, and certain f-150 vehicles, built on or after november 27, 1999.these vehicles have increased wheel stud and nut diameters from 12mm to 14mm.the wheel nut torque was increased from 100 ft-lb. To 150 ft-lb., respectively.odi has received three reports of wheels separating from 2000 model year expedition vehicles, including two crashes.two additional reports allege broken studs and/or loose wheel nuts.loose wheel nuts can allow the wheel to wobble and cause wheel stud breakage.there are no similar odi reports on 2000 model year lincoln navigator vehicles.the failures appear to be attributed to improper wheel nut torque; however, there is no evidence that there are torque quality deficiencies at the assembly plants.due to the mileages the incidents occurred, it is most likely that improper wheel nut torques were applied during servicing, because in all cases when loose wheels were re-torqued to a least 100 ft-lb., there were no failure re-occurrences.

Vehicles under investigation