Last year, I bought a pair of DaVinci cable couplers so that I could use single-bike length cables. During the season, I installed the derailleur one, but didn't need to touch the brake, so I left it for this winter's overhaul. Now I find that the brake cable "head" doesn't actually fit inside the coupler. Did I miss something here? I didn't think there were two different kinds/sizes of couplers. I got mine at Tandems East.
Another question: I learned, from experience, that putting one of these in the middle of a long span under the boom tube is a bad idea. I had to put a piece of foam tape to keep it from pinging at every bump. I am planning on putting it close to the rear BB shell to minimize that. Is there an ideal place for these?
The cable couplers on my tandem have 2 rubber donuts around them to keep from hitting the frame. I don't know what kind they are. You might look for couplers with donuts around them.
I have the o-rings as well, but it still makes a pretty solid ping when you have it at mid-span! Sure, it is better than metal on metal, but extremely annoying. I just put it at 4 inches from the captain BB shell. With any cable tension at all, it now cannot get to the frame.