Question re 6-wheeled trucks/bogies

[RobertInOntario]

I had a Roco Flat car with 3 axle trucks a few years ago. It had the same problem. I think it originaly had truck mount couplers Which I changed to body mount. I checked wheel gauge and Alignment. Same problem. Took it to LHS he called me and said its fixed. I picked it up and it still wouldn't stay on the track. I have several other cars with 3 axle trucks with no problem. Did you notice the wording in the first line of this reply

Thanks, Lester. I appreciate this info. BTW, not all of these coaches derail but there are 1-2 of them that are problematic. I wasn't sure by what you meant about the wording of the first line though. Thanks again, Rob