Shimano nexus 3-speed hub gear, yellow dot does not move when adjusting

Question

I have a bike with a Nexus 3 hub gear. Yesterday the shifting got out of whack, when set to gear 2, it was actually in gear 1, gear 3 was 2, and so on.

I looked up how to adjust it, and found that I have to rotate the adjustment knob until the yellow mark is between the lines in gear 2, after loosening the locking nut, as seen f.ex. here:

The problem is that when I rotate the adjustment knob (as in 1:13 in the video above), the yellow mark does not move. The yellow mark stays in the same spot even if the adjustment knob is all the way in or all the way out. So I cannot adjust it to be be between the lines. What could be happening? Am I doing something wrong or is my gear broken?

Answer 1

How dirty is the bike/gearbox? I'd wonder if its jammed up on some road debris or compacted dust.

When I worked on these before, the rear box-thing is removed by backing off a large grub screw, maybe two. This is exactly the same as when you remove the rear wheel for a new tube or tyre.

With the box dangling on the end of your cable, try and flush it with some brake cleaner or WD40/CRC556. You're trying to free the whole thing up.

Also, check the end of your axle, There should be a plunger visible that you can push in with light finger pressure, and it should return outward under spring pressure. This is what actuates the gearbox internally and it should also be easy to press.

You can also change gear at the bars while things are disconnected, without issue. That part of the linkages should also be light and easy to move with minimal effort.

Check those out and see what you find.