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On my 6-speed Brompton the two-speed gears suddenly stopped working. I still can operate the shifter (and the cable still seems to be under the expected tension), but the two-gear “derailleur” (chain pusher) doesn’t shift anymore.

First thing I did was thoroughly clean the chain tensioner and the chain pusher. (I even took the chain pusher off its mounting to clean the bottom as well.) And now the pusher moves a bit more, but certainly not enough.

I took a video of gearing system while shifting gears up and down and up and down:

Brompton-chain-pusher-even-after-clean-not-moving-fully_IMG_5794.mov on Dropbox

In the video the chain is on the larger sprocket and I hope the video shows clearly that the chain pusher for some reason doesn’t turn fully to the end of the stop screw and, as a consequence, canot shift the chain on the smaller sprocket.

Please note: The bike is in the video upside down. Also, the chain is not moving. However, the issue remains even when I turn the bike around and move the chain by pedalling.

Any idea how to fix this? Is it an issue with the inner cable?

Many thanks for any pointers!

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  • How do you know the cable is "under the expected tension"?
    – Michael come lately
    Commented Jun 11 at 13:27
  • I never worked on a brompton, but to me, it seems that the part of you derailleur that should be moving sideways does so reluctantly. Unless the manual says other, i suggest you apply more oil and try to move it (via the sift lever or by hand, if possible), and see if that improves things. if yes, repeat until all is well, then wipe off excess oil.
    – Burki
    Commented Jun 11 at 14:07
  • @Michaelcomelately When using the shifter the cable moves as I would expect (see video).
    – halloleo
    Commented Jun 12 at 2:50
  • It's clearly under some tension, but lining up the gear indexing requires the right tension. Since you only have two gears, the other stop screw might be doing the limiting on the other end, and the cable has too much (or too little) tension.
    – Michael come lately
    Commented Jun 12 at 15:35

1 Answer 1

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@Michaelcomelately's comment and the ideas from the wonderful people on the BromptonTalk mailing list got me to the solution:

I needed to give the gears a little more cable — just by screwing in the hollow cable screw on the shifter!

Background: I remember that -- before the clean -- I had screwed this screw out to make the chain pusher move the chain up onto the larger sprocket despite all the dirt in the system. Then, when I had cleaned everything, the cable was too tight to let the chain down on the smaller sprocket completely independent of the stopper screw in the chain pusher.

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