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I've listened that it is possible to modify the cage size of a rear derailleur.

For instance reducing a long (SGS) to a medium (GS) or short (SS) cage size.

Is it possible on all brands? Just shimano? Every model or just high specs?

Is possible to buy generic metal cages or you need to reuse a cage from other derailleur?

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    if it bolts on, you can try it
    – Paul H
    Commented Aug 10, 2022 at 14:36

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First of all, what derailleur do you have or do you wish to modify? That information is necessary as the answer is not necessarily "general."

Overall, many cages are detachable (at least those on high-end rear derailleurs), but there will be slight issues. The derailleurs of different capacities aren't just different from the size of the cage; the length of the body is also different. If you were to attach a long cage to a short cage derailleur, it won't hold as many teeth as the original long one.

You can buy a cage of the same series (let's say you are r7000 and you should only buy this instead of r8000 or r4700), or you can just buy the plates of the cage to change them.

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    I was thinking in reducing size for long cases on a Shimano DEORE(7sp), a XT(7sp) or an old Altus A10 (7sp). And would prefer medium GS than short SS
    – Daniel Perez
    Commented Aug 12, 2022 at 10:22
  • That is way too old, I don't think you can get new parts for them. I'd recommend you just buy a second-handed derailleur with your desired cage length. It will be cheap. I think people will want to sell their old derailleurs as a whole thing instead of taking it apart and having to deal with the rest.
    – Zyleyus
    Commented Aug 17, 2022 at 5:04
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The answer is maybe, and you probably won't find enough published information to know until you try to bolt it together.

Even within a single product family and generation, the parts vary:

Both have a total capacity of 41 teeth, with the 1x variant accepting a 10-51T cassette, and the 2x accepting a 10-45T cassette with a chainring difference of up to 10T.

In the expanded view documents, the parts for GS and SGS variants are listed:

The inner plate (closer to the spokes) for SGS is part Y3FA26000 for both 1x and 2x, but the outer plate is Y3FA98080 for for SGS 1x and Y3FB98050 for SGS 2x.

The P-Axle is Y5PV98060 for both, so outer plate might bolt on interchangeably, but the pivot to upper pulley geometry is different so if you swapped the outer plates between 1x and 2x, the upper pulley might sit too close or too far from the cassette, beyond the ability of the B-screw to compensate.

If you're working with older parts, the best approach may be to just buy a variety of derailleurs and try it. If it doesn't work out, clean the parts, reassemble and re-sell, potentially for profit.

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  • very informative, as you say probably the best is to buy cheap 2nd hand derailleurs and test them.
    – Daniel Perez
    Commented Aug 25, 2022 at 20:31

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