I'm new at this so if the answer to my problem is posted just 'point' me in the right direction.  I have a large lighted village layout and added two On30 trains this year.  One is a 2-6-0 Christmas train and the second (on a separate track) a DDC 4-6-0 freight train.  The problem is with the tender on the 4-6-0.  The rear trucks derail at various points on the loop...some on curves (22" E-Z track) but also randomly on straights.  There doesn't appear to be a problem with the track and I have rearranged cars to be sure the heaviest are immediately behind the tender.  The rearrangement actually seemed to be the solution.  It ran great for my Christmas party but has started the derail dance again.  I am out of ideas and hope someone here can help.  I have a great looking train that doesn't work.  No problem with the 2-6-0.

Thanks,
Arch