I have lots of passenger cars, and hate the gap on nearly all of them. I’m sure it’s don’t to make them able to negotiate tight curves so I guess I understand.
i posted a want add for a premier Amtrak diesel and ended up buying a F40PH-2 from CentralFan1976. While negotiating I also bought from him a 5 car set of amfleet cars.
First off, great guy. Excellent communicator, excellent packing, and quick shipping. Everything showed up and is absolutely beautiful. Everything is great except for the large gap between the cars. In talking to him, he mentioned he had drawn in CAD closer couplers for them in hopes of bringing them closer together but had yet to have them made and fitted. I have a 3d printer so he sent me the file before the cars even shipped.
That evening I printed a pair of them and instantly realized they wouldn’t couple! Talked to him some more and he explained he had lost the original CAD file and only had the STL. I knew I wanted this to work but my ape brain can barely spell CAD let alone work with any of the fancy programs that are designed to show me how stupid I am.
I ended up spending the day in tinkercad and on YouTube watching tutorials. There’s no way I’m at the level that I could completely redesign it, but I could clearly see the issue. The inside of the coupler was too tight and there was no way to make them slip together. I ended up figuring out how to cut part of the drawing off and placed it out of the way. Then I just started adding boxes to the face I had removed the horn from and then sliding the horn back in place. Took all day but I’m getting close.
Here’s the original car gap and some of the printing progress. 
