Weird derailing issue

[BestSnowman]

I've been breaking in a new locomotive (athearn SD40-2 Snoot) and discovered it will de-rail in a very specific situation on only one turnout. The turnout is a bachmann remote turnout.

The locomotive goes through all of my switches forward perfectly, and reverses through all of them perfectly except one. If I turn it around and run it forward through the turnout it runs fine. If I run it backwards and hold the relay switch down while it goes through the turnout it runs through it fine, however if I run it backwards through the turnout the rear truck takes the divergent route (incorrectly) but the front truck takes the non-divergent route (correctly). You can use your imagination as to the chaos that ensues, and this only ever happens on this locomotive. Even my older (20+ year old) rolling stock can navigate this turnout in either direction 99% of the time (and these are old cheap plastic wheelsets)

Suspecting the turnout was at fault I made a mess and ripped up some track and put a different turnout there to the same result. Then I tried changing the order of the wheels/axels on the rear trucks to see if maybe the first wheel set was out of gauge slightly or was picking the turnout (the truck has no problems going through the turnout facing the opposite direction).

This morning I decided to reverse and swap the trucks so at least it could operate facing the correct direction on my layout but I'm still concerned about this turnout. Has anyone else encountered this before? I've got it operational now but my concern is if it pops up again if/when I buy another locomotive.

[pdlethbridge]

Is the coupler hanging too low? Is there anything on the frame that could bump the truck?

[BestSnowman]

Is the coupler hanging too low? Is there anything on the frame that could bump the truck?

Nope, it did it with everything non-essential off. Literally running a frame, motor, and trucks. To make it weirder I reversed and swapped the trucks and I can't reproduce the problem at all.

[pdlethbridge]

So, the problem is solved???

[BestSnowman]

Technically yes, but I'm not sure why which makes me a bit leary as to whether its fixed or I just haven't been able to reproduce it recently.

I'm sure it'll be like all of my other stock, it will run perfectly until I'm showing it to somebody (I've actually stopped showing my Berk in action because it works perfectly until someone else is watching).

[Robertj668]

Bestsnowman
I actually had to video the train several times and catch the problems I was having.  I was great to have instant replay.
Robert

[mf5117]

You didn't really say which turnout it was . I had problems with a bachmann #5 turnout . The turnout had positive camber "a hump" the highest part of the hump was right before the metal frog , and the switch rivets were loose .this made my ho sd-40-2 derail many times . I also had 2 3" straights and a 2" straight together before the turnout which resulted in bad track alignment IE humps and valleys . I also found that my sd-40-2 does not like 18" radius curves . If it is not laid perfect its gonna jump . Also I took a NMRA guage and checked my wheel truck ,flange, guage, and track guage. What really helped was removing the short pcs from the layout , and getting or replacing the turnout , also I just remembered that one of the rail's was loose from the tie's on the grey EZ TRACK road bed .

sd-40-2's don't like crooked or hump or bumpy track ...... just my 3 cents

[mf5117]

you know i use to get so mad . i would show somebody my layout and how cool it was and bingo      "gomez" derail recks the whole 9 yards. then i would get, an un huh sure . lol but i would be running 5 trains at once . and my sloopy track work would bite me in the ying yang . but hey i learned  . jim banner yampa bob , kinda like my old sponcers them yets ain't happened yet

[mf5117]

my #5 EZ TRACK switch was also at the end of the 18" radius . I also could not run the sd40-2 in either direction . would derail coming from the curve into the switch and would run fine coming from the straight mainline over the switch, then into the curve . I changed and remove the switch down one 9" straight from the curve . I have 4 sets in my layout so I can go in either direction . on the 18" and 22" radius parts of the layout .

it was recommended I gauge my couplers check my trucks . get an nmra gauge . flanges wheel sets etc etc but I just had a track problem .   

my 4-8-4 sante fa also would jump and derail in the same place .

[BestSnowman]

I hadn't thought of video taping it,  the only time i could get it to navigate the switch was when it was slow enough I could actually watch it.

It is a #5 turnout but it leads to a small parallel siding for temporary parking of small freight service so my SD40-2 won't ever (intentionally) need to go in it. I had kind of noticed that even my smaller locomotives bounced a bit when traversing turnouts.

I'll have to try some of your ideas.

[Stephen D. Richards]

You could also try a small piece of plexiglass (2x5 inches) with a set of trucks mounted on them and hand push the car over the track.  This is amazing the results you will see from your track.  It is a very good tool for locating track defects.  Micro Mark sells one but very easy to make.  Just a thought.    Stephen