I recently changed the shifter cable on my bicycle, which has a Shimano 8-speed Alfine internal gear hub, and a twist shifter (Nexus Revo-Shift). Shimano provides PDFs of the dealer manuals, with details on how to install, and uninstall. I thought I would document it for myself, with pictures.
It’s not too complex. I actually did it first without looking at the manuals. It is actually pretty simple. The twist shift mechanism is straightforward, and you can figure it out after opening it up: there is only one screw to remove to get into it.
The first thing to do is to remove the cable at the hub end. You put the shifter into gear 1, release tension on the cable by inserting a small (#2) Allen key into a hole at the hub and rotating the pulley mechanism, then pull the cable fixing bolt off its notch. You may have to use a pair of pliers. Here is the diagram from the dealer manual (DM-SG0003-03-ENG.pdf).
Remove the cable fixing bolt, and put it aside.
Removing the shifter itself is much easier. First, get it off the handle bar. Then, peel back the rubber grip and pull it off. Remove the small screw holding on the cover plate, and take the plate off. Remove the adjustment bolt. Be careful because it’s in three pieces, including a small spring that may fly out or roll away.
To actually remove the cable, I found that it helps to put a right-angle crimp in it near the “nub”. That angles the nub out of the housing allowing you to pull the cable out.
Re-installing is straightforward once you have the new cable and housing in. Follow the manual for torque specs, and detailed adjustment instructions. For adjustment, put the shifter in gear 4, and look at the top of the hub. You should see two yellow line segments. Screw the adjuster to align the segments: they should overlap by more than ⅔ of the width of the lines.
A note about the cable. I got Jagwire Road Elite Sealed Shift cable kit. The week before I had replaced my entire brake system and used the Jagwire Road Elite Sealed Brake cables, and found them to work really well. Very smooth and firm: no hint of sponginess. The Elite Sealed system has a full-length internal plastic (Teflon?) liner, which is pre-lubricated. The cable is “polymer coated” (I think it’s Teflon). This keeps grit and moisture out. The housing is compressionless.
In any case, this shift cable does not seem to work well with the Revo-Shift and the Alfine hub. During a 10 minute test ride over relatively flat ground, I found it tended to stick between 4 and 5, especially shifting down: that is when the tension is being reduced, and the internal hub shifts from a high “register” to low. The hub would be hung up on 5 even when I had shifted down to 1.
All in all, I learnt a lot about my bike and the internal hub system doing this. It was a couple of hours well spent. I will have to put in a different shifter cable, but it will go easier.
UPDATE: The problem was with adjustment. I did not put enough tension on the cable to start with. Adjusting the base tension got rid of the "no shift" issue.