Unit failures are always catastrophic.
One of Fleetpro’s customers took delivery of (239) E 350’s with this transmission and lost (70) transmissions within the first 60,000 miles.
Failure begins with noise and roughness in the driveline then can be detected by a sharp ear and is most noticeable when idling in drive with the wheels suspended to rotate freely. Rotation can be seen as jerky and rough. Noise will be present. Imminent failure at that point is within 3-10 days. Upon failure the driveline is locked up and the driveshaft must be removed in order to tow the vehicle.
The apparent running change at the plant was a change in the size of the T6 thrust bearing, which is integral to the planetary. Subsequent to this change the existing sun gear machining may not have been compatible to the new thrust bearing resulting in premature thrust bearing failure. Ford has redesigned the sun gear machining profile as of early 2012 and the bearing is also under review for revision. Units built at the Livonia plant from October 2010 through January 2012 are potentially subject to this early failure.
Consult your local Ford dealer for details.