Backing issues

The nature of the beast. Trains- even real ones- are subject to tension and compression problems.

Even more specifically in the model world, light cars, combined with or less than ideal coupler systems under compression load tend to put high forces in a corner.

Trains are better pulled than pushed in most cases.

While searching to find you pictures, I came across this forum post

https://ogrforum.com/...1#153463017335878531

This photo by @Ray of sunshine  while intended to show a different problem is semi-relevant

You can see how both trucks are "twisting" compared to the straight track and the couplers are not in a straight line parallel with the track. Now imagine this same setup on a curve and the couplers shift and are trying to push the truck right off the track. Fixed couplers attached to the truck that follow and "steer" the truck (or the truck attempts to steer them) VS flexible coupler to truck connection.

In addition to checking coupler alignment/and proper mating as suggested by Vernon, other things to consider that will improve the likelihood of successfully backing the train include:

1. Arranging the cars such that the heaviest ones are at the front just behind the locomotive (and tender if applicable) and the lightest cars are at the rear of the train.
2. Adding weight to cars that are lighter than NMRA recommendations.
3. Backing more slowly.

@El Tejon

Interesting issue, Rick. By comparison, I have all modern Lionel on my Fastrack layout with only 036 curves. My freight cars all have sprung metal trucks and my aluminum passenger cars all have the metal trucks and couplers. There is some sideways movement of the couplers when they back up, especially with the passenger cars' longer-shanked couplers. And while they move way over to either side of the car end, the cars still move backwards without derailing. But then, aluminum passenger cars are heavier cars.

I've backed my trains up at fairly fast speeds on the mainlines (with my finger ready on the halt button), just to see if they could do it, with no derailments of either the freight or passenger trains. I even have a partial S curve on the passenger mainline and they go through it in reverse with no issues. Of course I keep the axles lubed and everything well-maintained. But no derailments from doing that. I have only one Fasttrack switch, but have never had any problems with it, whether the freight cars are going forward or backward.

I'm wondering of your track and older Postwar rolling stock would have anything to do with causing the derailments in reverse, especially on curves or through the switches. Maybe the solution would be to put some weight at the ends of the cars as SteveH suggested.

Thanks for the input. One thing I love about this hobby is you are never finished!