MCI Drive Shaft Safety Loop Failures
In the fall of 2011, network contacts made ODI aware of four (4) incidents of drive shaft failure on the subject buses involving a loss of vehicle control.Two of the incidents were relatively low speed non-crash events; and two resulted in motor coach rollovers.All four events showed signs of a common failure mode.The incidents and crashes studied during this investigation all resulted from a series of complex events that began with the the yoke journal ears on the drive shafts fracturing.Once the drive shaft failed. it was not adequately contained by a drive shaft safety loop or structure.The spinning and unrestrained drive shaft caused severe damage to components on the steerable tag axle at the rear of the vehicle and created a forced steering condition.Once the rear of the bus was being forcibly steered by the tag axle, the driver lost control of the vehicle.These conclusions are based on the forensics evidence and testing conducted by the Vehicle Research and Test Center (VRTC).The VRTC test report is attached to this closing resume that provides details on how the test center was able to conclusively identify the defective components on the buses and demonstrate the sequence of events that caused the buses to crash.Prior to the drive shaft failure events, there were no indications of improper maintenance or that maintenance was required that would have prevented the incidents.Additionally, the U-joints on the incident vehicles were found to be in good working condition at the time of the failure. Finally, records of driver interviews indicated a sudden onset of the failure with no warning.Following the VRTC testing, MCI issued recall 14V-335 involving certain model year 1993-1995 102DL3 motor coaches manufactured November 1992 to January 1995, and 2006 and 2008 D4505 motor coaches manufactured June 2005 to April 2008.The affected buses are equipped with a drive shaft with a compressed length of 30 inches or less (allowing it to escape containment if it fails), a steerable trailing tag axle equipped with a system that changes the axle caster when the vehicle is in reverse travel and no electronic stability control (ESC).Recall 14V-335 addresses the concerns of this investigation.The ODI report cited above can be viewed at www-odi.nhtsa.dot.gov/owners/SearchNHTSAID: ODI Number 10447575.