Or you sense a disturbance in the force and figure it’s better to be safe than sorry. Have you been sorry before? Of course! More times than we care to admit.
About the coupler issue, I would do a good diagnosis before trying anything. I would roll two of the offending cars slowly to see what is the difference in height and what could be the cause. It could be many things (slope, track, coupler, wheels, etc.). The height difference might be too high for the couplers you are considering.
Simon
I don’t why this fixed some uncoupling issues, but;
I was experiencing uncoupling issues with Walthers 70 ton hoppers. The hoppers would uncouple at random places on the track. I replaced all the couplers with KDs. I still had problems. I double checked each coupler with a Kadee height gauge. I still had problems. I made sure each coupling jaw on the coupler was free to move. I still had problems. I don’t why I did this, but I put a drop of CRC 2-26 on the head of each coupler. End of uncoupling problems. I can only speculate that the couplings were binding and causing them to uncouple. Maybe the coupling jaws could move further and clamp better? The lubricant let the couplers move around some? It’s a year since I lubricated the couplers and I still don’t have any uncoupling issues.
Might be worth a try before buying all new couplers.
Interesting, I don’t think it fix my issue but worth knowing 
This issue would be true if a modeler was being naughty and not following standard best practices like checking rollinstock coupler height with the good ol Kadee height gauge and making necessary adjustments to all rolling stock. For those of us who grew up with kits, this practice became firmly engrained as part of a check list of getting the model out of the box and on the layout.
But you know what they say about assumptions (Under Siege II).
I agree. I had the exact same problem as you are having and simply loosening the nails and letting the track have less of an abrupt change is the solution, and it is an easy one. I just slipped some match sticks or popsicle sticks under the track at one point and it fixed the problem. I really didn’t do much except relieve the tension on the track and let it make it’s own curve which was more gradual. This is one reason that I always test and retest my track when installing it and I never apply the ballast until I know the track is perfect. Don’t waste your money on couplers just fix your track.
I assume that all of your couplers are at the proper height as compared to the Kadee couple height gauge. If some couplers are low and some are high you will have problems like you are having. If some are high but none are low then that might be acceptable because you can have some margin of error, but it’s better not too. Kadee makes couplers with under shanks and over shanks to correct height problems. Fixing that might be the solution that you need.
All couplers are at the correct height according to my Kadee guage
IMO, it can’t hurt to pick some up pack of Kadee shelf couplers and give’m a try. Likely you have some tank cars that could use the shelf couplers if you don’t end up needing them on the long cars so no waste either way. I still need to change out the stock couplers on my tank cars so I need to order some myself.
BTW, it looks like others have used shelf couplers for exactly the same reason you started this topic [;)]
Here is some comments for the SF type at MB Klein:
http://www.modeltrainstuff.com/Kadee-HO-Metal-SF-Shelf-Coupler-Metal-Mediu-p/kad-118.htm
So I guess I’m earning the moniker I put in my siggy by going against the prevailing advise here. [:P] Or am I just simply being a contrarian in this case?
Just thought I’d round up this discussion by letting you all know that I purchased both 118 & 119 Kadee shelf couplers and installed them on the 2 car racks.
So far they’ve been round the layout more than 50 times and no de-coupling [:)]
thanks everyone
Awesome! [:D]
and Bob’s your uncle!
Thanks for the update.
Glad the solution for you was effective and inexpensive.
Regards, Ed
This is how OP was persuaded to buy the Kadee #118 and #119. Seven years later, someone had the same problem (Atlas Rescue Forum), and I introduced him to this thread. I commented that the shelf couplers and Walthers swing pockets are essential for passing through the tight crossover (scissors) of #6. However, he did not reach the same conclusion.
I admit that my guidance was poor. On the other hand, I feel that the trend in the hobby world has changed. This is because a tendency towards realism, or rather, a tendency to not accept anything that is not faithful to the real thing, has become widespread.
The idea that a model is a scaled-down version of a real rollingstock is wrong. A senior colleague of mine said this 50 years ago, that the real rollingstock is merely a motif for the model. With what little time I have left of my life, I feel strongly that I don’t want to be swayed by the real thing anymore.
O-scale 0-8-0 IHB U-4a Switcher (AHM/Rivarossi 1970)
Yes. No matter how close a model looks like the real thing, it is merely a representation.
I am “modeling” a real railroad, but my goal has always been realism and plausibility rather than accuracy. When a visitor recognized a place without a visible business name, even though the models are compressed and don’t closely match the prototype, I knew that I had achieved that goal.
That’s right. No one cares if Da Vinci painted the Mona Lisa faithfully or not.
SPSF Kodachrome scheme, 50’ boxcar（MDC-Roundhouse 1987）