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I need to replace the pulley wheels on my rd-m3100. The T-pulley is close to worn down (ninja-starry), even though the G-pulley still has some life left. Unfortunately the original replacement part, y5ft98030, is impossible to get hold of in my country, and importing the part from abroad is prohibitively expensive (a new derailleur is cheaper). There is a 105 11T pulley wheel set that in the seller's description supposedly fits other 9/10 speed Shimano derailleurs (but it is not listed as compatible on Shimano's site).

Does anyone have any experience with mixing pulleys that are not strictly compatible according to Shimano's site? The pulleys to be replaced are both 11-tooth bushing-type nylon/plastic(?) pulleys on a 9 speed RD (on a 8-speed bike :) ) There is also a BBB(brand) 11T pulley set for sale, but this is really not made specifically for my derailleur either.

Any experience based advice on what the best option is given the original part is not an option?

EDIT: The 105-pulley set (RD-5701) WP-Y5XH98120 is compatible with rd-m2000 and rd-m3000, and my original pulley (y5ft98030) is also the pulley supplied with these two derailleurs. Isn't it then likely that the 105-set also fits my rd-m3100?

EDIT2: The Y5XH98120 and the y5ft98030 are both approximately 8.2mm wide between the metal covers from my own measurements. The major difference seems to be that the y5ft98030 has less material/is slimmer on the T-pulley towards the circumference of the pulleywheel.

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There are two things that really matter when replacing pulleys on Shimano derailleurs with units not officially compatible:

  • Tooth count
  • Spacing, or in other words total thickness (the dimension that if it were different from original, the two pieces of the cage would be spaced differently)

They name or classify the sets in frustratingly arbitrary ways, in terms of the name that shows up on the package. The way it actually works is that there are a few RDs that need their own very specific pulleys because of tooth count and/or the cage has inset elements rather than being flat, but most aren't like this.

Unfortunately Shimano doesn't publish the key thickness measurement, but there's not actually much variance outside the highly specific ones, so in practice many of the derailleurs have multiple sets that can work. When I've had to go with something not officially compatible, I just measure until I find a hit and usually it's worked out.

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    Another variable can be the ID of the pulley's mounting hole. There's generally a sleeve or bushing provided that can be added or removed to match the other size.
    – Criggie
    Commented Jan 17 at 7:40
  • @Criggie Among Shimano RDs and pulleys is there variance there? Commented Jan 17 at 8:48
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    The RD-m3000 and 3100 actually have the same part-numbers for outer plate, pulley-screws and pulley wheels. So I might just take my chances with the 105 pulley.
    – WornChain
    Commented Jan 17 at 10:52
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I would not bother with trying to find a compatible Shimano part. There are third party replacement pulleys from manufacturers like BBB, Tacx, etc that come with a set of adapter bushings to fit different derailleurs. I have found that these work just as well as low to mid tier original parts.

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  • I think Tacx hasn't been producing pulley wheels for several years since the company was absorbed by others. Not sure about the bottles. Commented Jan 17 at 19:33
  • BBB pulley wheels are indeed available and the OP mentions these in the question "but this is really not made specifically for my derailleur either". Are they compatible? BDP-21 look like they should be, but are needlessly expensive. Perhhaps rather RolerBoys. One advantage of alternative pulley wheels is that they often offer sealed bearings where the original only had bushings prone to dirt ingress. Commented Jan 17 at 19:50
  • @VladimirFГероямслава it's true that the Tacx pulleys haven't been made in years but there seems to be a lot of old stock available for buying. Yes, they are compatible because of the set of adapters that comes with the pulleys. No, they aren't specifically made for that exact derailleur, but if it needs to be the specific part then nothing but y5ft98030 will do and the whole question is moot.
    – ojs
    Commented Jan 17 at 20:00
  • @ojs The ones available are "BBB RollerBoys BDP-02", but in the detailed description they are called BDP-01, and are supposedly compatible with shimano 9/10/11. They are more expensive than the 105 tough. None of these non-original parts have any guarantee at all to fit. And that is why I ask. There is no reason why a non-shimano random pulley with 11T would fit better than the 105 that I at least know have the same screw, and some indication of compatibility from cross-compatibility with other parts. But I do not know, and haven't tried it, hoping others have.
    – WornChain
    Commented Jan 17 at 20:14
  • @WornChain personally I would expect that a third-party pulley that is intended to be compatible between brands and comes with a set of adapters has better chances to fit than one that is made specifically to fit a different model. I think your only chance is to buy all models and try them out one by one.
    – ojs
    Commented Jan 17 at 21:00
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Today I did the swap with no issues. As stated, the mentioned pulleys are the same width of 8.2mm between the two metal covers. They are the same number of teeth, and the fastening bolt is the same for the two pulleys. Below is a picture of the two sets (new vs 10.000km, I rode them for another 600km), G-pulleys on top, T-pulleys bottom. Good luck to anyone in need of this information. The package claimed compatibility with rd-m3000, rd-m3100 was not listed on it.

enter image description here

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    I think the main thing is match the # of teeth, and roughly match # of speeds. More teeth = bigger wheel. That may affect shifting, although often the effect is slight. For # of speeds, that affects thickness, although you should have some leeway. Glad your problem was resolved.
    – Weiwen Ng
    Commented May 17 at 23:02
  • IMO it is strange that Shimano does not list these two parts as compatible. I am guessing the rdm3100 came out after the 3000 and they just forgot to update their compatibility charts given all the facts i've presented. Alternatively, there is some mismatch that Shimano finds unacceptable (the slight thickness difference?) for this RD but not for other similar RDs that use the same original pulleys as my RD did. But yes, glad it worked out.
    – WornChain
    Commented May 18 at 0:42
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I have found that jockey/pulley wheels are almost all compatible, the only thing I had to ensure was that the wheel spun freely once it was refitted back into derailleur cage and everything was tightened up again. I have done this to 6 or more Shimano rear derailleurs.

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    You might have been lucky/ running some common size deraileur. More details to highlight compatibility between parts that are not listed as compatible by shimano would be very helpfull to other people in doubt facing the same issue with difficulty getting the Shimano listed compatbile part. (width between covers is also usefull as this is info Shimano doesn't give on their site).
    – WornChain
    Commented Jun 11 at 10:08

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