DRIVER'S SIDE BUCKET SEAT BACK BROKE RESULTING IN SEAT BACK RESTING ON REAR PASSENGER SEAT AND THROWING DRIVER TOWARD REAR OF VEHICLE. BOLTS HOLDING THE SEAT IN PLACE WERE BROKEN OFF, (SHEARED), AS REPORTED BY REPAIRMAN. REPAIRMAN STATES THAT BOLTS AND SEAT FRAME TOTALLY FAILED DUE TO POOR WELDS AND SMALL SEAT BOLTS.