NHTSA Complaint #763464 — 1989 CHEVROLET C3500

SEPARATION OF WHEEL, HUB AND AXLE ASSEMBLY FROM VEHICLE WHILE UNDERWAY. INSPECTION OF THE COMPONENTS REVEALED A CRACKED BEARING RETAINING NUT, WHICH ALLOWED THE NUT'S INSIDE DIAMETER TO EXPAND AND SLIDE OFF THE THREADED HUB. RECOVERED PARTS INCLUDE THE NUT, KEY, AND RETAINER RING, ALL OF WHICH APPEAR TO HAVE BEEN PROPERLY ASSEMBLED. ALSO DAMAGED AT THE TIME OF FAILURE WAS THE AXLE SHAFT, WHICH FRACTURED AT THE OUTBOARD EDGE OF THE SPLINE AREA, ABOUT 3 INCHES FROM THE TIP. I COULD NOT DETERMINE IF THE AXLE FRACTURE OCCURRED WHILE THE AXLE WAS IN THE HOUSING OR IF THE DAMAGE WAS THE RESULT OF THE AXLE EXTENDING OUT OF THE HOUSING OR THE SUBSEQUENT TUMBLING OF THE WHEEL/AXLE ASSEMBLY AFTER SEPARATION. THIS IS A NON-POSITRACK REAREND SO THE AXLE FAILURE COULD NOT HAVE OCCURRED VERY LONG BEFORE THE ASSEMBLY SEPERATION. THIS INCIDENT OCCURRED IN A RURAL AREA AND RESULTED IN NO DAMAGE OTHER THAN TO THE REAR AXLE HOUSING AND BRAKE BACKING PLATE. ALL AXLE BEARINGS TURN FREELY. THERE IS NO VISUALLY APPARENT CAUSE FOR THE FRACTURE OF THE BEARING RETAINER NUT. THIS IS NOT A PART NORMALLY SUBJECT TO WEAR OR PREVENTITIVE MAINTENANCE REPLACEMENT.