Preliminary Evaluation PE97-001: REAR AXLE SEPARATION FROM VEHICLE

THE SINGLE CONSUMER COMPLAINT RECEIVED BY NHTSA REPORTED AN INCIDENT IN WHICH APPLICATION OF THE SERVICE BRAKES OF THE SUBJECT VEHICLE PRECIPITATED AN UNFOREWARNED LOSS OF VEHICLE CONTROL AS THE LEFT REAR AXLE SEPARATED FROM THE VEHICLE.INSPECTION OF THE VEHICLE FOLLOWING THE INCIDENT DISCLOSED THAT THE LEFT REAR DUAL WHEELS HAD JAMMED INTO THE FENDER WELL AS THE AXLE SEPARATED FROM THE LEFT LEAF SPRING ASSEMBLY.THE NUTS WERE REPORTED MISSING FROM THE TWO U-BOLTS WHICH CLAMP THE REAR AXLE TO THE LEAF SPRINGS.THE INCIDENT OCCURRED ON A VEHICLE WITH A REPORTED ODOMETER READING OF 397 MILES.NO ADDITIONAL CONSUMER COMPLAINTS REGARDING THE ALLEGED DEFECT IN THE SUBJECT VEHICLES WERE RECEIVED BY THIS AGENCY SINCE THIS PE WAS INITIATED.INQUIRY TO THE MANUFACTURER DISCLOSED NO OTHER CONSUMER COMPLAINTS OR FIELD REPORTS OF SIMILAR NATURE, AND THREE WARRANTY CLAIMS WERE IDENTIFIED AS POTENTIALLY RELEVANT.THESE DATA APPLY TO THE 11,499 C/D 30-SERIES VEHICLES SOLD THROUGH MID-FEBRUARY, 1997, FROM THE TOTAL OF 27,385 BUILT AT GM'S FLINT ASSEMBLY PLANT.THE INQUIRY WAS LIMITED TO VEHICLES PRODUCED AT FLINT BECAUSE THE LOW MILEAGE OF THE COMPLAINANT VEHICLE SUGGESTED THAT ASSEMBLY/PRODUCTIION PROCEDURES MIGHT BE A SOURCE OF THE ISSUE.ODI ALSO CONTACTED THE GENERAL SERVICE ADMINISTRATION'S FLEET MANAGEMENT OFFICE AND DISCUSSED THE ISSUE.THEY SENT REQUESTS TO ALL OF THEIR REGIONAL FLEET MANAGERS ACROSS THE UNITED STATES, FOR ANY INFORMATION OR REPORTS OF FAILURES WITHIN THE GSA'S TOTAL FLEET OF SEVERAL HUNDRED TRUCKS. NO INCIDENT REPORTS WERE RECEIVED IN RESPONSE TO THESE INQUIRIES.THE APPLICATION OF PROPER TORQUES ON THE U-BOLT NUTS DURING VEHICLE ASSEMBLY IS ACCOMPLISHED BY AUTOMATED PNEUMATIC TOOLS THAT REQUIRE THE STATION OPERATOR TO ABSERVE AND MARK THE TORQUED ASSEMBLIES ACCORDING TO A COLOR CODE, AND TO NOTE ANY HIGH- OR LOW-TORQUE CONDITIONS ON AN INSPECTION TICKET.STATISTICAL REPORTS FOR THE ASSEMBLY FASTENING SYSTEM ARE PULLED TWICE PER SHIFT AND REVIEWED BY POWER TOOL PERSONNEL TO ENSURE THAT THE TOOL IS BEING USED AND THAT IT IS PERFORMING PROPERLY TO APPLY TORQUES WITHIN SPECIFIED ENGINEERING TOLERANCES.THE SINGLE CONSUMER COMPLAINT REPORTED FAILURE TO HAVE OCCURRED IN DECEMBER 1996. THE THREE WARRANTY CLAIMS WERE FILED IN NOVEMBER 1996, JANUARY 1997 AND FEBRUARY 1997.

THIS TYPE OF FAILURE WOULD LIKELY BE DETECTED AND REPORTED VERY EARLY IN THE SERVICE LIFE OF THE VEHICLE, SO IT IS ALSO LIKELY THAT THE AFFECTED VEHICLES WERE PRODUCED OVER A PERIOD OF SEVERAL WEEKS AS OPPOSED TO A SINGLE PRODUCTION SHIFT, THE LATTER OF WHICH MIGHT INDICATE AN ASSEMBLY TOOL CALIBRATION OF OPERATOR PROBLEM DURING A SPECIFIC PERIOD OF TIME.THE SPREAD OF THE WARRANTY CLAIMS OVER SEVERAL WEEKS, TOGETHER WITH THE SINGLE INCIDENT REPORT, SUGGESTS THAT THESE INCIDENTS WERE OF A RANDOM NATURE, AS OPPOSED TO BEING INDICATORS OF A SYSTEMATIC ERROR IN THE PRODUCTION EQUIPMENT, THE ASSEMBLY PROCESS, OR THE QUALITY CONTROL MEASURES TAKEN.A SAFETY DEFECT TREND HAS NOT BEEN IDENTIFIED, AND THIS PE HAS BEEN CLOSED.THE CLOSING OF THIS INVESTIGATION DOES NOT CONSTITUTE A FINDING BY NHTSA THAT NO SAFETY-RELATED DEFECT EXISTS.THE AGENCY RESERVES THE RIGHT TO TAKE FURTHER ACTION IF WARRANTED BY THE CIRCUMSTANCES.