NHTSA Preliminary Evaluation PE87015

ANALYSIS:ALLEGEDLY, DURING BRAKE APPLICATION THE DISC BRAKE CALIPERSSEIZE, RESULTING IN EXCESSIVE PULL AND/OR FRONT BRAKE LOCK-UP.SOMEREPORTS CITE A COMPLETE LOSS OF VEHICLE CONTROL RESULTING IN UNFOREWARNEDAND UNAVOIDABLE TRAVEL INTO OPPOSING TRAFFIC LANES.CONSUMERS CLAIM THATSERVICE PERSONNEL HAVE CONSISTENTLY ATTRIBUTED THE PROBLEM TO THE USE OFPHENOLIC PISTONS WHICH OVERHEAT AND SEIZE IN THE CALIPER BORES.INFORMATION PROVIDED BY THE MANUFACTURER DISCLOSED THE COMPLAINT, ACCIDENT,AND INJURY STATISTICS TABULATED ABOVE.OTHER MANUFACTURER-SUPPLIED DATADISCLOSED THAT TWO DESIGN CHANGES WITH POTENTIAL RELEVANCE TO THIS MATTERWERE MADE DURING THE PRODUCTION YEARS IN QUESTION.IN OCTOBER 1981, THESPECIFICATION OF THE MAXIMUM OUTSIDE DIAMETER OF THE PISTON WAS DECREASEDBY 0.0250 MM AND THE MINIMUM INSIDE DIAMETER OF THE CALIPER PISTON BOREINCREASED BY 0.024 MM.THESE CHANGES WERE MADE TO REDUCE THE POSSIBILITYOF PREMATURE WEAR OF THE FRONT DISC BRAKE PADS.A SECOND DESIGN REVISIONWAS MADE IN SEPTEMBER 1986 TO REDUCE INADVERTENT CHIPPING OF THE CALIPERPISTONS DURING BRAKE PAD REPLACEMENT.WARRANTY CLAIM DATA WERE INCONCLUS-IVE IN IDENTIFYING A FAILURE TREND ACCOMPANIED BY RISK OF ACCIDENTS.THE HISTORY OF BRONCO BRAKE PULL/DRIFT COMPLAINTS DISCLOSED THAT FORD HADKNOWLEDGE OF THE PROBLEM.AN AUGUST 1986, FORD TRUCK INTEROFFICE LETTERDISCUSSED THE PHENOMENON AND PROVIDED SUGGESTIONS TO REMEDY THE PROBLEMIN THE FIELD.THE CONDITION WAS DEFINED AS RECESSION STEER, MANIFEST TOTHE VEHICLE OPERATOR AS DRIFT OR PULL UPON BRAKE APPLICATION.IN FACT,THE SENSATION WAS ATTRIBUTED TO A NET STEER TO THE LEFT WHEN THE FRONTSUSPENSION MOVES REARWARD UNDER BRAKING FORCES.CONCLUSION:SEIZURE OF THE FRONT CALIPER PISTONS HAS NOT BEEN IDENTIFIEDAS THE ORIGIN OF THE ALLEGED PROBLEM.ADDITIONALLY, THE HISTORICAL DATAALLEGING LOSS OF VEHICLE CONTROL, ACCIDENTS, AND INJURIES DO NOT IDENTIFYA SAFETY-RELATED DEFECT IN EITHER THE BRAKING OR SUSPENSION SYSTEM OF THESUBJECT VEHICLES.======