Anonymous says:

There are several causes for couplers to do what you are seeing. 1) The coupler spring is broken or gone, so it will not center correctly. 2) The coupler spring is pinched between the box it is sitting in and the cover (centering problem again). 3) If the coupler is in its box correctly and does not move freely side to side then the cover may be fastened down too tight and is pinching the coupler. 4) The height of the coupler is too high or too low. The wheel problem you mentioned will also contribute to this. To check these conditions purchase a NMRA Track gauge. The gauge has locations to check the wheel spacing as well as the track spacing and several other features for the gauge/scale (e.g. HO, N etc.) that you are running. Also Kadee products have a wonderful coupler height gauge that I use. As it has been within the last 6 months where I have started to try to run the rolling stock that was my fathers and mine from 40+ years ago and watched the same conditions that you are seeing (cars un-coupling, jumping the track etc. the same as 40 years ago and these were quality box cars not cheap ones) that I am now going through each one and replacing the couplers (with Kadee or similar quality knuckle couplers) and metal wheels (if you do this gauge the wheels before installing them they are not always correct out of the box). The first 10 that I have fixed have been fantastic no more problems (forward or backward). Lastly also check the track for wide or narrow spots and clearances at guard rails. I Hope this helps.