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I have a Shimano RD-TY20 derailleur with a date code of 1989. It is mounted on a frame which is marked as 1984. This frame is made of steel, and the derailleur hanger is part of the frame.

I want to modernize the drivetrain (Please reserve your judgement on whether this makes sense: It does not.), but I'm having doubts about whether I will be able to mount more modern RDs. Here is an exploded view of RD-TY20 showing how the RD is attached to the frame (see elements 18 and 19 under "Direct Attachment Type"):

enter image description here

(Image source: https://manualzz.com/doc/53870261/shimano-rd-ty20-pemindah-gigi-belakang-exploded-view )

A bolt is stuck through the RD, which is then attached to the frame's hanger with a nut. The bolt is narrower than the M10 bolts built into modern RDs, but the nut that secures it to the frame seems to be about the same width.

What is this kind of attachment style called? Where can I get more modern parts with this attachment style, if at all?

Googling for "Direct Attachment derailleur" returns some relatively recent innovation and is of no help.

Of note, perhaps, is that the integrated hanger on this frame does seem to have some threading in the hole, but I don't have any way to check if it would accept an M10 bolt.

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The frame almost certainly uses an M10x1 thread and standard hanger/dropout shape that most new RDs will mount to. By 1984, if there were any frames anywhere being produced using previous standards (Simplex etc) they were an extreme rarity. (Many bikes around the world continued in this time and up to today to just not have a derailleur hanger and instead take claw-style rear derailleurs. But as far as dropouts with integral derailleur mounting, by this time the Campagnolo-derived standard we have today had basically won out).

I've handled the Tourney models like you have. Using the sleeve nut to mount the derailleur allows them to play a trick that other designs can't: the nut shoulder is pinching the dropout, such that you can manually set the angle of the parallelogram to be whatever you want. Note yours doesn't have a b-screw, which most designs use in conjunction with the stop tooth on the hanger to do the same thing.

I don't totally understand the logic of why they were given this feature. It might have had something to do with allowing it to work as a repair part for bikes with hangers that didn't have the stop tooth or had something else nonstandard about the hanger (such as Simplex). More bikes like this were still around at the time. It may also have just been a way of giving maximum freedom to dial in this adjustment to help work around the limitations of being a non-slant-parallelogram RD.

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  • I've ordered the new derailleur. I'll give updates (& accept answer) when it arrives, hopefully you are correct haha. The frame in question is (almost certainly) made by Favorit, a Czechoslovakian company. The RD hanger does have a stop tooth, but I sourced the frame and RD from different bins so who knows what was on there originally. In this region, from comparable eras, there were many strange designs, with "hooked" RDs still being somewhat popular. Simplex, as you say, is present on many of these bicycles.
    – jayded-bee
    Oct 27, 2022 at 10:53
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    It lives! Thanks for the vote of confidence. I am now running a 9 speed chain+cassette with a Claris 2000 RD with downtube friction shifters on this frame. Can't believe what a world of difference this makes.
    – jayded-bee
    Nov 6, 2022 at 17:22

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