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I recently bought a bicycle that came with a 7-speed microshift-M21 rear derailleur for which they have used a microSHIFT TS38 Thumb Tap Shifter. I observed that the rear gear shifting is not accurate which on further observation looks like the LOWER LEVER on the shifter is making more clicks (step increments) than it should. I believe it should make only one step of gear change on either of the lower or upper lever presses.

So what exactly I observed is that when I press the LOWER lever on the shifter to its full range (till where max it can go), it makes a total of 3 clicks (step-changes) while pressing the upper lever correctly makes only one step change.

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Any idea if this is a normal behavior of these microSHIFT-TS38 Thumb Tap Shifters? I checked everything else like the cable tension and L/H screws on the derailleur which are fine. Nowhere on their website is it written as a feature that it supports more than one shift using the same lever press in extended press.

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    I don't have any experience with this particular shifter, but it's extremely common to have the multiple-downshift capability. On the other hand, wonky derailleur action can be caused by a multitude of factors other than the shifter itself, such as an out-of-alignment derailleur hanger, too-tight cable routing, or contaminated cables. I'd seriously expect one of those things to be the culprit rather than a faulty shifter.
    – Paweł
    Commented Feb 12, 2023 at 9:06
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    @Paweł consider adding that as an answer; it's indeed a common thing in MTB and road shifters.
    – Weiwen Ng
    Commented Feb 12, 2023 at 13:00

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While I don't have any experience with this particular shifter, multiple-downshift capability is a very common feature in both MTB and road shifters. On the other hand, I highly doubt that this is the culprit of bad shifting, as the multiple-downshift mechanism is not responsible for the indexing action. In my experience, bad shifting is usually caused by:

  • dirt deposition and rusting of shifting cables - this is especially relevant in old or poorly maintained bikes, as well as those ridden in winter
  • improper cable routing - too tight bends significantly increase internal cable friction which can make shifting imprecise or nigh-on impossible
  • improper shifting cable tension
  • bent derailleur hanger - it's very easy to bend the hanger in a crash or by lying the bike on the ground and even a new hanger will most likely not be perfectly straight in a frame due to manufacturing tolerances, therefore it should be straightened with a specialized tool. A bent hanger will make indexing the whole cassette impossible
  • improper lubrication

If the bike was ridden extensively in inclement weather I'd also have taken a look at the rear derailleur to check if the parallelogram is working smoothly and the return spring action is adequate.

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  • I thoroughly checked the rear derailleur cable and found that it had accumulated dirt on the rearmost harness, so I cleaned it properly and voila, the gears are smooth back again :), and yes, I also checked it, my thumb shifter is able to make three downshifts in one extended press of the lower lever, so yes it is a feature.
    – Akay
    Commented Feb 22, 2023 at 12:45

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