USRA 0-6-0

[deepest]

     I have the above locomotive with short haul tender. It uses a draw bar 'coupler' between the two. The tender derails consistently even on straight stretches. 
     Can I replace the draw bar arrangement with something elso to corect this derailing situation ?
     Thanks for your advice -

     deepest

[on30gn15]

What parts have been looked at closely to see if there is something, such as molding flash, obstructing free movement of the trucks or the drawbar?
What scale the 0-6-0 is can make a difference in what to look for and do - post gives no scale info.

[deepest]

sri, it's HO scale
I'm hoping to replace the coupling completely and eliminate the draw bar arrangement - I have - weighted - the tender as a partial, yet unsatisfactory solution

[on30gn15]

Okay. I have several of them, and I think it is Jonathan who has quite a few 0-6-0.
Before saying anything else, I'd suggest posting this in the HO section, it will get far more attention there.

On all the ones I have, the tender drawbar has a peg which slides side to side in a slot under cab. It moves freely enough that locos will go around curves down to 9 inch radius for me.
See if something is causing peg on end of drawbar to snag on something in slot, or the flat to snag on something under cab rear.

Next thing is to examine the wheels and trucks.
Do you have a NMRA HO standards gauge? NMRA being National Model Railroad Association. It will tell you whether wheels are in gauge. either too close together or too far apart will cause trouble.
So will wheels which are off-center, or not square to the axle.

Weight can help - to a point.

You have heard the phrase, three point suspension?
What a lot of folks do with car and tender trucks is turn one kingpin screw down to where the truck rotates freely but does not rock much if any. The other truck screw is turned down a bit less so as to allow that truck to rock slightly. Doing so helps cars track over irregularities in the rails.

After that, I'm out of ideas for the moment.

[brokenrail]

The weight is probably the last thing you want to do after checking the gauge of the wheels and loosening the truck screws.If you do not have a gauge and the ability to take the tender trucks off and remove the axles you can compare the gauge of the wheels of a known good trouble free car that you have that does not derail by putting  your tender axles/wheel assembly's next to the car wheels  and hold them together side by side and line up the back side of the wheels with a known styrieght edge and then take a look at the other side closely .The backs of the wheels should line up .If not then you make your adjustment by pulling out or pushing in a little on the wheel. It is a crude method that takes some time ,a good eye and a steady hand,but will have good results if you take your time.
Johnny