Tender derailing

[CG04]

A little background first.  I got my first HO train set about 20 years ago and found it in my mother's garage about a month ago.  It had never been opened.  The name on the box is AHM.  Anyway, I decided it was time to try it out.  It works like a charm.  Several weeks ago I acquired a 4-8-4 steam locomotive but the rear drive wheels kept coming apart.  I sent it to Bachmann for repairs and they sent me a brand new one with DCC on Board.  NOW FOR THE PROBLEM I'M HAVING....As soon as the tender hits the first curved track, it derails.  Is this because the curves are too sharp???
What are my options?  Am I stuck with something that will not work on my layout?  I have it set up on a 4X8 sheet of plywood.

Needing help here.......

[Jake]

It depends, what roadname is it? Bachmann Northerns are sold in ATSF, New York Central, Southern Pacific, and I think that's it. I'm not sure what to do in the case of the any of them as I did not ever have the NYC, or Esspee though I DID have the ATSF and never got any problems on curves down to 18" radius.

[SteamGene]

Check the tender wheels to make sure they are in gauge.  It could also be that the truck is too tight. 
Gene

[kevin2083]

also check the wires from the tender to the loco and make sure they can flex freely

[CG04]

A little background first.  I got my first HO train set about 20 years ago and found it in my mother's garage about a month ago.  It had never been opened.  The name on the box is AHM.  Anyway, I decided it was time to try it out.  It works like a charm.  Several weeks ago I acquired a 4-8-4 steam locomotive but the rear drive wheels kept coming apart.  I sent it to Bachmann for repairs and they sent me a brand new one with DCC on Board.  NOW FOR THE PROBLEM I'M HAVING....As soon as the tender hits the first curved track, it derails.  Is this because the curves are too sharp???
What are my options?  Am I stuck with something that will not work on my layout?  I have it set up on a 4X8 sheet of plywood.

Needing help here.......

[Stephen D. Richards]

I had the same problem with a 4-8-2.  Seems the wires from the Tender to the Engine were not flexible enough and were literally throwing the Tender of the tracks anytime the loco went through a turn.  Stephen

[ebtnut]

DCC ready locos, with all those wires between the loco and tender, do tend to derail the tender, especially on the smaller locos.  Make sure there is as much flex as possible.  Also, it often helps to put some added weight inside the tender.  Just make sure the weight doesn't touch or interfere with any of the electronics.  Your Bachmann instruction sheet will show you how to take the tender body apart.