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I have a big-box-bike 18 speed that I ride around the neighborhood for exercise. Recently it stopped staying in the rear gear I put it in -- I roll the gear selector where I want it, but as soon as I let go the gear slides back to 6. If I hold the gear I want the bike stays in that gear, but as soon as I let go the spring in the derailleur drags it back to six. I assume there's some sort of a ratcheting mechanism or pawl somewhere that holds the derailleur in the gear I select, I just don't know where it is.

I'd rather just replace the broken part then get a new bike -- but before I order something I thought I'd ask the professionals -- what should I be ordering to fix this problem?

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  • You say you "roll' the shifter. That sounds like some sort of gripshift (example). These are often cheaply made and rather flimsy. I recently had one fail on me; its partner had already died. The failure mode is often a bit of plastic breaking off, and not repairable except by replacing the shifter. But is it a gripshift (aka revoshift etc.)?
    – Chris H
    Commented Aug 3, 2023 at 8:11

3 Answers 3

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Yes, there is a pawl or similar mechanism in every indexed shifter that will not let the derailleur move once you have shifted. Whatever that mechanism is, it seems to have broken in your shifter. Unfortunately, shifters are not generally repairable once their internal mechanisms fail. However, they usually last a long time.

Normally, you would want to seek warranty service if you're in the warranty period. With a big box store, I have a feeling they'd just give you a new bike if they agreed, because they wouldn't be set up to change just one faulty component. If this were a bike bought from a regular store, they would install a new shifter.

Sometimes, shifting problems may be caused by gunk in the shift mechanism. Sometimes this can be remedied with a spray of WD-40. Intuitively, I don't think that this is the cause of your failure, but it's worth mentioning in general.

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    So just to clarify -- it is the shifter (not in the derailleur)? Makes sense that it wouldn't be repairable, but yeah I have no problem buying a replacement shifter. I assume I'd need to get the same number of speeds, because a 7 speed shifter wouldn't work very will on a 6 speed cassette.
    – Sidney
    Commented Aug 2, 2023 at 18:29
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    @Sidney It sounds like the shifter, yes. If it were something in the derailleur, it would need to overcome the resistance provided by the detent in the shifter.
    – Weiwen Ng
    Commented Aug 2, 2023 at 20:21
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    In a twist shifter, it's often a much simpler mechanism - just simple detents feed into plastic and a spring to locate in them. They're like friction shifters with added index points, unlike trigger-style mechanisms.
    – Chris H
    Commented Aug 3, 2023 at 8:14
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    @Sidney Not just the same number of speeds, but also compatible with that particular derailleur. There are some cases where a shifter from brand X will not work correctly with a derailleur from brand Y even if the shifter matches the number of sprockets on the cassette. That said, this may come down to trial and error if the derailleur can’t be positively identified.
    – Austin Hemmelgarn
    Commented Aug 3, 2023 at 13:53
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Indeed, there is usually a mechanism in the shifter that holds a cable in position. That cable keeps the derailleur in the right gear. If this mechanism is broken, the cable slides back to the most slack position, which in your case makes it go to the 6th (smallest) cog. When you say 'roll', I assume you have a twister shifter? Take care that you order one that is compatible with your derailleur brand. I'm not certain for 6 speed, but for many speeds, the derailleurs for one brand will not pull the correct amount of cable for another brands' same speed derailleur.

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  • Yeah, it's a twist-shifter, like the accelerator on a motor cycle. So just to clarify, if the derailleur requires 3 cm of travel from one end of the cassette to another and a twist-shifter's full range of motion was 1.5 cm it wouldn't work out as I'd only be able to get to half the gears? Not that I'd want to do that, just trying to understand the fundamental compatibility problem.
    – Sidney
    Commented Aug 3, 2023 at 18:20
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It's possible that the cable just needs to be tightened. Over time, the cables can stretch. Look for a barrel adjuster like this where the cable exits the shifter, or maybe somewhere else along the cable:

bike cable barrel adjuster

By twisting the slimmer main body you can shorten the effective length of the cable, and then tighten down the collar to lock it in place.

If there isn't enough adjustment left, you may have to adjust the clamp at the end of the cable. Put the shifter in the most relaxed position for its spring, shorten the barrel adjuster, then loosen the clamp, pull through cable with pliers, and tighten the clamp. This is pretty hard. Then use the barrel adjuster to set the final length.

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    How does adjusting cable tension stop the shifter from sliding back to smallest gear?
    – ojs
    Commented Aug 4, 2023 at 18:41
  • I may have misunderstood the question - I thought the bike was slipping back one gear, which can happen when the shifter and derailleur are slightly out of sync.
    – tilde
    Commented Aug 4, 2023 at 20:07
  • The question says "I roll the gear selector where I want it, but as soon as I let go the gear slides back to 6"
    – ojs
    Commented Aug 5, 2023 at 10:21

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