Derailment going backwards on curves

[trainlivebob]

I have a 1950 Lionel 2023 diesel that runs good in forward, at very high and low speeds.  However when I run it backwards (no cars or dummy) it derails on curves (O27) at any speed.

My other 2023 does not have this problem.  Ive looked at both of them to compare and cant find an obvious difference.  The truck springs look good and it turns side to side the same.

The only gut feel I have is that the side to side slop of the rear truck wheels to the track may be bigger on the faulty engine, but I have not measured it.  If that is the case, could the pickup roller fall off the center rail, thus forcing the derailment?

Any suggestions as to what to look for or diagnostic tricks would be appreciated.

Bob

[lionelsoni]

Symptoms on a vertical-motor locomotive that show up only in one direction are often due to a missing or damaged thrust bearing in the motor.

[Leverettrailfan]

I don't have my service manual on me right now, nor do I own a 2023 or other similar model of ALCo FA. That said, what comes to mind for me as a possible culprit is stiff old wiring. I think it's worthwhile to operate your two 2023s with the shells off, so you can observe the behavior of the rear truck and notice if anything seems different between the two. Looking up pictures of the 2023 chassis, it appears that the E-Unit is effectively mounted to the rear truck. With all the wires going to it, I can certainly see how wiring could potentially cause issues. Why it isn't an issue in forwards I can't exactly explain, but it wouldn't shock me if the wires coming out of the E-Unit are causing the truck to want to pivot the wrong way as soon as it gets a chance.
I definitely think you could be onto something with the 'side to side' slop. I think if the locomotive's truck could swivel too much, you could probably get the rollers jammed on the track- iirc the 623 uses the same sort of trucks, and the rollers stick out pretty far from the truck.
Either way, pulling off the shell and inspecting things as you run your engine could definitely help spot the issue. Good luck, eager to hear your findings.

-Ellie

[trainlivebob]

Thanks for the suggestion Bob.  I looked at the armature shaft axial movement on both units and cannot see any difference.  Stiil looking for some difference.

[trainlivebob]

Thanks Ellie.

I looked at the wiring and the unit with the problem has been rewired with flex wiring in a nice manner.  Moving the truck side to side it is totally free to move and compares well with the other loco.  I will try running and watching the units on the track.  Maybe a little video if I can get my assistant to help.

Bob

[trainlivebob]

Well, after some experimentation and observation, I discovered the problem and got it fixed.

The key observation was finding out it only derailed in one direction where the rear truck was turning left.  Going right was no problem.

You were right Ellie, wiring was it.  the new wiring was taut in one direction as it went around the curve.  I could not feel any restriction manually at all but I could see some wires were pulled mostly straight against the horn relay.  I thought I was going to have to add length to the wires, but after rearranging them there was enough slack to correct the problem.  Goes around the O27 track and switches great.

This is a very subtle fix and I can see why.  After watching my slo-mo video, the center rail roller is very near off the rail when it works.  When it doesnt, sparks fly as the roller end up between the rails.  Its a very delicate balancing act so just a minor restriction caused the issue.

Thanks everyone for the help.

Bob

 

[Leverettrailfan]

Bob, glad to hear you got it sorted!! Sometimes the problem is invisible until you can catch it in action. I've certainly been puzzled at times.

-Ellie