While changing my LGB coaches to use my version of Raby's Knuckle coupler (http://www.thingiverse.com/thing:1989545), I found that very old LGB coaches were made with the hook and eye as an integral part of the bogie, and so cannot be easily replaced.
I therefore modified the bogie I had used on the 12 ton wagon, so that it now works with these old LGB coaches. I also redesigned the axle so that it uses 337 mm ball bearings. This should mean that the wheels /bearings have a longer life than the original metal on plastic design. The wheels can press on the brakes if the axles slide sideways, but if this is a problem, some washers on the axles should keep the wheels centred. Or you can imagine the scraping sounds as realistic flange sounds when going around corners!
The bogie is quite difficult to refit, as the back brakes need some very strong "persuasion" to allow the bogie to be fitted in the frame (see photo). However, they are quite strong, and provided that they have no weakness from print faults, they seem to accept the bending and spring right back.
I have found this works much better with PLA, as ABS is too brittle and snaps when you put the ball bearings in.
There is a small "square" part on the "bottom" of the "Peg" that is supposed to help it print better. It is a separate part in the 123 drawing so you can remove it if you like.
The stl also has two "bars" across the bogie that are proud of the rest of the surface and that bear on the LGB coach frame . You may need to make these a little less high to keep the bogie movement smooth when the frame is securely screwed to the coach body. Again, these are separate parts in the 123D drawing, so that they can be easily modified.
Allow the PLA to cool slowly.
I am not sure if this is a "real thing", or if it just happens to fit with my experience, but I found that my first prints, which I removed as soon as they were finished, did snap/break when I put in the bearing. Since then I have improved the bearing hole design, but an similar bogie that I allowed to cool/anneal overnight at about 25 deg c seemed less brittle and did not snap.
Just an Idea, but it may help!.