A few of the questions we need answered………..Advertisement
At appx 1:55 in the video, you can hear the “click” of the coupler breaking apart.
Slack action in the coupler is the most likely cause of the knuckle break as well as the draft gear (shock absorber) being overstressed to the point it gives out. Upon starting or stopping a long heavy train, power is distributed to each car successively from the engine to the cars one by one. The draft gear in each coupler takes on the shock of the sudden movement in turn for each car.
In this case, the longer heavier train, along with the longitudinal forces in play with the extra power unit in the middle may have been too much.
Let us know what you think caused the knuckle (coupler) to let go. We would love to hear your opinion!