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I have a Microshift Marvo XE rear mech, 9 speed, on a little recumbent I made. It's been a decent derailleur, but recently, when in the smallest cog (11-32 cassette back there) it does the "clunk-clunk-clunk" thing as I pedal. Upon close inspection, when it's shifted all the way to the smallest cog, you can see that the teeth grab/push the chain plates on the outboard side about once per rotation. As the chain revolves around toward the top, the tension pulls it and seats it, so the clunking is just the slack being taken up. Normally it's just a fairly annoying noise, but it can morph into some skipping when it's really acting up.

This sounds like a simple limit screw issue -- back out the H screw a touch so the cage moves outboard a little more, and it should be all good. But that's not it.

After much testing, I figured out that the limit screw (and cable tension) are fine. It shifts very well across the entire range, except for not seating all the way in the smallest cog position on its own. BUT, If I push the derailleur parallelogram outboard with my finger after making the shift to the smallest cog, it moves about 1mm more (or less, its barely perceptible), and it's silent and smooth from there on out. However, shifted down with the shifter alone, it never reaches that position, always hesitating about that 1mm inboard.

There's nothing impeding the movement in any way, and the push required to do it manually is very slight. The spring just doesn't seem to get it done. (I could easily reach this with my hand while riding and adjust it caveman style, but I don't like sticking my fingers in a wheel spinning at the >=18 mph that this one would be for this shift! And they're small wheels, so they're spinning a lot faster than 622s would)

I tried messing with the C screw a little to see if that would free it up or change the angle enough to make it go away, but it didn't help, and shifting got worse, so I put it back to the original spot I had it. The mech wasn't too dirty, but it got a wash today then I lubed every pivot I could find. No luck yet.

I'll probably toss a Sora 9 speed on there since they're cheap, and I have one on the nearly identical wife's bike, and it doesn't have this problem, however that mech gives up a couple of links of capacity on the drive train, causing some potential issues with the setup I've got, which needs, IIRC 1-3 more links of capacity than the Sora's got (43).

Anyone else seen this in a rear derailleur and have ideas to coax the thing into moving all the way back on its own?

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  • I wonder if the mech is very slightly bent? Start by completely disassembling and cleaning it, then lube on reassembly.
    – Criggie
    Jul 14, 2022 at 9:21
  • This might be due to a worn chain or cog assembly. Jul 14, 2022 at 12:25
  • I thought that at first, but chain has <1,500 miles on it, clean riding, lubed, ditto the cassette. Mech is straight (checked against steel ruler edge). I'm leaning toward overstretched spring at this point, maybe from a hit. Small wheels mean it's down low. There are a couple minor scratches down there, but may have been enough.
    – user36575
    Jul 14, 2022 at 19:49

3 Answers 3

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If noone else’s suggestion works, and nothing is bent, put a 1mm M10 washer on the derailleur bolt, between it and the frame. That will buy you some time.

The cable adjustment and limit screws will need re-setting accordingly.

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  • That would of course require adjusting the whole setup accordingly, else all the other gears will have problems. It might solve the smallest-cog problem, if it's something to do with the derailleur itself, but if it's cable friction then you might end up having the same problem again in the end. If we're going to use hacks I'd rather try to somehow aid the spring, perhaps with some rubber bands. Jul 14, 2022 at 12:45
  • @leftaroundabout I would consider elastic bands a horrible hack. They are not very durable. We used to use the washer trick on older generation SRAM derailleurs that wouldn't find the small sprocket on some frames. Obviously we eliminate cable and alignment problems before moving onto this modification!
    – Noise
    Jul 14, 2022 at 18:20
  • I may try a 1mm spacer there. I can 3d print one easily enough. That way, if it's just a matter of its being at the end of the spring pull where the strength just isn't there, it might get the job done. Should only require adjustment of the limit screws, really. I can usually get one of these installed and shifting smooth in <5 minutes.
    – user36575
    Jul 14, 2022 at 19:40
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    Spacer solved it. I thought maybe this is a result of my hand-made dropout material thickness (1/4" or 6.35mm) being just a little slimmer than what many bike dropouts are, but I've made 4 bikes with this, and tested 2 of the others just now (one with a Shimano Sora, other with a Microshift Mezzo) and they are both fine w/o spacers. I suspect I damage the spring in mine and it doesn't have the power it did before when it's nearly compressed. Taking up the slack physically puts the shift movement into the zone where it's still got enough oomph. I'll replace it & set this one aside as a spare.
    – user36575
    Jul 14, 2022 at 20:31
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    I had to adjust the limit screws and also the tension about 4 clicks tighter, and it was all good.
    – user36575
    Jul 14, 2022 at 20:33
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The problem is likely to be too much friction somewhere.

This could be in the cables. Some would replace them immediately, I'd inspect, clean and possibly add a bit of grease or even oil.

Even if you've cleaned it, there's a chance the friction is from something in the derailleur - either a bit of grit or gummy grease. I've had to take mine off to soak and scrub it.

Recheck your limit screw on the stand after either of these, to avoid the chance of dropping the chain between cog and dropout on a test ride

If you've used it really hard, there's a chance it's actually weaker than it was, perhaps the spring stretching or a bit of looseness causing the parallelogram to sit wrong and need extra travel. In that case you'd need a new derailleur, because replacing the springs isn't normally meant to be possible.

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  • Cables and housing are pretty new, clean, and as mentioned, derailleur was cleaned and thoroughly lubed in order to try to remedy. I wonder though if I didn't ding it at some point and stretch (and weaken) the spring. Parallelogram is still nice and straight, so nothing obvious there, but clearly something's keeping it from moving that last mm.
    – user36575
    Jul 14, 2022 at 19:42
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    Missed the chance to say "There's a fraction too much friction"
    – Criggie
    Jul 14, 2022 at 21:05
  • @WPNoviceCoder Where does the derailleur sit if you undo the inner cable's pinch bolt? In theory it should drop to the highest gear exactly. This would help show if the cause is cabling and above, or if its in the derailleur mech/mount itself.
    – Criggie
    Jul 14, 2022 at 21:06
  • It sits in the same spot -- just inboard of the true stop. (I determined that before posting the Q.) As mentioned in OP, the spring action could only seat the DR within about 1mm of final rest against limit screw. Spacing it outward as described above put it back in the zone where the spring could still seat it entirely against the limit screw. That's why I suspect a physical hit overstretched the spring -- weakening it a bit in its near-compressed state, in effect lengthening it a tiny bit.
    – user36575
    Jul 15, 2022 at 14:06
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Derailleurs do wear out over time. Especially with a hard life, in bad weather, the bushings in the pivots eventually have too much play and result in various symptoms of poor shifting. Not puling enough tension to return the derailleur to its most outboard position is one of these symptoms.

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  • Hi, welcome to bicycles. If your answer is "it's worn out and needs replacing" you should clearly state that.
    – DavidW
    Jul 11, 2023 at 3:07

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