For those of you who hang on my every word, read every post expecting enlightenment, and dispel my wisdom upon your friends; don't tell me about it. That is creepy. Keep tellin' your friends, but lighten up a bit. If you are one of those, you might remember a problem I experienced with the Nuvinci hub freezing on my hero Byron. A couple of winters ago,it was freezing up and I assumed it was the shift interface unit. Recently a reader commented on that post and said he had experienced a similar problem with the unit and found water freezing in the cable housing. With my usual sense of humility, I dismissed that as irrelevant and then placed a space heater near my cables. Hmm, there was an immediate improvement in, or elimination of, the problem. So I took the time to look at the cable housing, found, what looked like a small crack, removed the cable and housing,
and watched it explode as a mass of corroded braiding.
Obviously that needed attention. I bought some more housing,
a couple of cables and replaced the whole mess.
I recommend following the directions carefully if you do this because the double cable shifter, although a brilliant design, can be confusing and intimidating.
After havimg replaced the cables and the damaged housing, I routed them over rather than under the bottom bracket. That should prevent a low point to collect moisture as well as potential damage from debris and obstructions. I waited a few days, let the bike sit in the cold (>-10 windchill), and guess what? It shifted beautifully, it wasn't the shift interface at all, just water in a housing.
It's hard to believe but, I might have been mistaken in my original hypothesis.