In visiting Model Railroad Forums I've seen several post where railroaders have used American Limited Diaphragms with success. As an FYI my mainline minimum radius is 29", the minimum radius in my yard is 18". I only run my Daylight passenger train on my mainline.
I had an old pair of Walthers 933-429 diaphragms on hand and decided to give them a try on my Cary E7 shells rather than toss them. I have to say in just taking them out of the package they look pathetic. Installing them was the pits!!!! Filmsy doesn't even come close to describing them. It took the better part of an afternoon to get them installed, getting them to fit correctly is a real task. I had to remove them four times and start over. The bottom line is they are working and looking pretty good.
The E7s in the foreground are my Cary shells, the two E9As are Proto2000s.
The above picture shows the Walthers diaphragms installed. They work pretty good but I think it's because of the combination of the heavy weight from the cast metal Cary shells and the Athearn SD40-2 frames, there is no way they could derail with all that weight.
I have gone to brass connecting rods between my diesels so the diaphragms can't interfere with coupler action between the A & B units.
The picture above is a pair of my Proto2000 E9As with the stock Proto2000 diaphragms reinstalled for comparison. I tried something new with this pair of E9s by putting a thin layer of white grease on the diaphragm plates. That made the plates of the diaphragms super slippery and at this point they still derail going through 18" radius turnouts in my yard. This pair is also connected together by a brass rod instead of couplers.
This picture shows the Cary E7s with Walthers Diaphragms on Atlas 18" radius Snap Track, tight but working OK.
The Proto 2000 diaphragms with the white grease sill have problems on a 18" radius. The Proto 2000 E series are marginal even without the diaphragms on an 18" radius. The Athearn SD40-2 frame negotiates an 18" radius much better than the Proto 2000s.
I have ordered a pair of American Limited 9500 SP Wide diaphragms and I will add to this post after they arrive. I plan to install one on the Cary B shell and the other on my Athearn Daylight baggage car to see if they will work without problems.
To help prevent problems I have replaced all the Kadee #5 couplers on my Daylight passenger cars with Kadee #119 Shelf Couplers. The Kadee #119 Couplers and the solid brass rod between diesels positively stops all accidental uncoupling.
There is a downside to using Kadee Shelf Couplers, it is very difficult to uncouple anything using them without either a uncoupler magnet between the rails or a Kadee #241 uncoupling tool. The 241 tool isn't easy to use after installing diaphragms, the diaphragms hinder the viewing angle of the couplers.
The combination of shelf couplers and the solid rod between diesels makes it extremely difficult to disconnect the locomotives from the passenger cars without an uncoupler. I find it best to keep a Kadee #322 magnet handy to drop between the rails for easy uncoupling.
Using solid brass coupling rods between diesels also takes care of small differences in motor RPM between powered units, it stops the jerking action.