Possibly a worn out coupler (the little scissor type ones not the articulated ones). I found that over use can make them spread out and that means they wont have the tension to hold the rest of the consist behind the coupler when going round the layout.
I had this between the centre dividing coaches which prevented me running two sets together. However to solve this I took the couplers off the spare power cars and the problem went away.
I prefer ro run mine with the Motorised Car leading so that any problems with derailment means the coaches that suffer are left behind, and there isnt some all might pile up where the power car keeps pushing the train after its crashed.
Still fun to watch if its not your stock! hehe :evil1:
The Shinkansens are better as they use drop pins to hold the coaches together and unless the train gets aerobatic there is no way these will come apart. So the trains can be extended upto 20 coaches quite easily.
