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Replaced front OEM Grip Shift SH-F3 barrel shifter with Twist Grip M25-7 shifter on Vintage consumer-type bike w Shimano GS100 and 3 chainrings (x7 cassette).

Mounting went fine, cable run is clean and clear. Backed off barrel a few turns and with shifter on “1” and slack taken out connected the cable to the derailleur. Minimal adjustment needed to the L limit. But the shift from “1” to “2” skips the middle chainring completely and takes the cage all the way to the largest, and there’s no apparent index adjustment - nor instructions or even a product listing on the website (it was an amazon purchase of a “Shimano-compatible” - please limit the chastising). I’ve reached out to MicroShift for support but no response.

I do find it interesting that the new shifter 1-2-3 markings are not equidistant - there is greater spacing between 1-2 than 2-3 which I don’t get. For what it’s worth no amazon comments similar to my problem.

In my understanding Shimano have massive market share and that the mass-consumer bike market is highly standardized in components, altogether suggesting I’ve done something wrong - that’s where you come in - even though the mechanics of these things aren’t rocket science.

Any advice would be appreciated.

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  • Most grip-twist shifters not indexed in the front. That's to say, one click upon twisting doesn't equal one shift. It typically takes 2-3 clicks to get the chain to move to the next chainwheel. Essentially they are friction shifters with detents built in. I realize this isn't your problem but it's related because I'd like to know how far you turn the shifter when the derailleur does the 1 to 3. Typically it means the cable has too much initial tension, or that you may not be in the low position on the shifter to begin with
    – Jeff
    Jul 31 '20 at 22:53
  • These particular shifters seem to have indexed front shifting as well as rear. These are very low end shifters and so I might suspect poor build quality or some cable misrouting inside the shifter. The different marker spacing also occurs in shifters from other brands, for example SRAM's MRX Comp 3x7 speed shifters.
    – Armand
    Aug 1 '20 at 1:42
  • Jeff, you’re right - I’ve misused “index” and detents is more accurate; we took apart the old to troubleshoot and that’s clearly the design. I should have added that info and that the old unit had equally-spaced detents. @Armand also from the beginning suspected some incompatibility but also couldn’t figure why anyone would make one with such a huge throw - rationalizing that with Shimano share spacing standard for consumer bikes would have been established long ago. We’ll shift focus to a new brand. Probably another thread on it somewhere, but any trusted aftermarket names or marketplaces? Aug 1 '20 at 12:49
  • @TRR I've used the MRX Comp 3x7 in the past; it's not high-end, but functioned fine. I believe Shimano Revo shifters are available in 3x7 as well. I have had poor quality and/or counterfeit item problems with items that were shipped to me from China so I personally try to buy from the usual US mountain bike parts places or US vendors on ebay or Amazon. If you buy from a local bike shop or someplace like an REI store you can have them install it as well.
    – Armand
    Aug 2 '20 at 2:29
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My first thought is that the new shifter isn't compatible with the chainring spacing, but unless this group has a super-narrow profile I can't think of one that would be as wide as a typical first-to-third chainring spacing.

In my experience, the markings on twist-type shifters are not always equidistant, and may be due to non-linear throw of the derailleur or non-linear take-up of cable in the shifter. Check that the cable is properly routed through the shifter as well as to the derailleur pinch bolt. I have seen the latter cause this issue.

If you have an alternate derailleur (top swing vs. bottom swing) you can try that if space allows.

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