One of the things that really bothers me when viewing a passenger train is that most of the time one sees a great deal of daylight between coaches. Another issue is that coaches out of the box have couplings that make the coaches way too far apart. I'll discuss simple ways to improve matters.
These are some Mk 1s I improved (well, I think I did).
Making working corridor connections is not difficult, nor does it take a lot of time and you can use materials that are probably already to hand.
Photocopy paper which is on the heavy side
0.020" Evergreen pastic sheet
Take the corridor connection off the coach to be treated and mark the dimensions of this on the paper:
Note there is a half line at the center of the corridor outline.
Cut the connections as shown. Use the back of an Xacto knife to score the fold lines:
Fold each piece and cut the half line in the center. Colour the paper black.
Now thread two connections together to obtain a concertina:
Make end/rubbing plates from the plastic sheet using the original coach corridor as a guide:
Glue the plates to the paper concertinas, and paint black:
The surface of the rubbing plates needs to be smooth since coaches negotiating points and curves have sliding contact at this location and any resistance will cause a derailment. Here's one I did earlier:
I should probably say that you can get the MJT design from Dart Castings. These come with white metal end plates and etched rubbing plates, as shown here.
Now, as to distance between coaches. If your coaches stay in more or less fixed rakes, ie. there is no coach shunting/marshalling on the layout, you can use something I learned from Tony Wright. This method is detailed in BRM's Right Track 4 DVD, "Detailing and Improving RTR". (By the way, these DVDs will play on my DVD player but not on my BlueRay).
The method involves:
1) removing the proprietary coupling system.
2) fixing copper clad strip behind the buffer beam. The surface of the strip should be flush with the buffer beam so will need shimming.
3) 0.45" nickel silver wire is soldered to the copper clad strip. On one end of the coach in a hook shape and on the other a loop.
These pictures illustrate what I mean:
Before painting, you will want to test the coupling on your layout. Check it through curves and points and especially check while propelling. If the coaches are too close for your layout, buffers will lock so its a simple matter of tweaking the distance of the hook from the bufferbeam until all is well. The loop should be in line with the buffer heads. For corridor coaches this is less critical since the working corridor described above will stop the coaches getting too close. For non-corridor coaches you might need to solder a piece of wire across the loop to prevent the buffers from getting too close:
This coupling method works very well and permits propelling. I put Kadees on the ends of coaches that will couple to the locomotive.
One other thing, if the coaches are quite close coupled, as mine are, you may find that there is a lot of pressure on the end plates. Too much pressure will reduce the ability to slide when going round curves and through points causing derailments.
The solution is make the corridor concertina only three corridor widths wide instead of four. When coupled there should be very little rubbing plate pressure while the corridors stay in contact.