Thanks!!  I'll get at it tonight.

Here's a second on 'thefavoritespot.'  I have purchased quite a bit from them through eBay and they have always been very good both on price and delivery.  Check out their listings; some of the stuff is not for bid, but is Buy It Now.

I finally got to measure the wheel spacing with calipers and the rear truck on the tender is definitely the problem.  The rearmost set of wheels (4 sets on the tender) is just about 1/32 wider than all the others.  Now the question is can the wheel spacing be reduced, and how?

The problem is definitely with the trucks on the tender.  I put another locomotive (4-6-0 like the first one) on the same track with the identical rolling stock and it runs perfectly, very smooth and strong.  A friend has an HO gauge he is going to bring over and we'll get it fixed.  Both front and rear trucks seem to have complete, free motion; I'm thinking of just replacing the entire rear truck assembly.

Thanks for your help.

Thanks guys, I'll be checking things out over the weekend when I'll have time to play.
The drawbar hole I'm using is the one furthest from the loco and the DCC wires seem to be clear although a bit stiff.  I tend to run the loco at slower rather than faster speed, but I have tried a variety to see if it matters and it doesn't seem to be a factor.  Also I have not tried to add weight under the tender.
FYI...When I finished the layout and started running the 4-6-0 it seemed okay for a short time.  Then the tender back truck started to derail just after completing a 22"R 90.  After some quick research and experimentation a rearrangement of cars with the heaviest immediately after the tender 'fixed' the problem.  A couple of days ago, as I was inspecting before running, I discovered that the pin on the tender wasn't engaged with the drawbar and the DCC wires were infact the only connection.  I reconnected the tender through the first or outer hole and started up.  Almost immediately the tender started to derail again for the first time since the 'rearrangement.'  I did try switching holes but that didn't cure the problem.  Running just loco and tender didn't work either.

Thanks Bob, I'll check that.  I have a feeling that the problem is the DDC wires from the loco to the tender, but the wheel problem makes sense too.

Arch

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