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Pretty tricky fix this morning.
I got some parts from an old guy on CL, including a hardly used RD-7700. He was upfront about why it was cheap--missing a little helicoil that holds the cable pinch bolt (Shimano's design, not on the EV doc but there are forum posts about it). Years ago it had backed out, but he bent it trying to get it reseated. He considered it 'parts only', but for $15 I figured I'd try repairing it.
Difficult because the pinch bolt flange is tiny, and the existing hole is about the largest you can have on there. Because of tight dimensions some easy fixes are out, and I don't have M5 helicoils, couldn't find any that small locally. And I didn't want to pay ~$12-20 online without trying 'the easiest' option first: filing/shaping a stainless M5 nylock nut to fit on the flange backside. Fiddly because the backside isn't flat, there is a height limit (spring), and side limit (inside corner of the parallelogram).
I filed both the top & bottom to reduce the height, gave the bottom a contour to match the flange, the top a contour to match the spring. And 3 of 6 wrench flats were filed round. When in smallest cog, the nut seats near that 'VIA' mark (the blurry glint betrays that I touched the corner with a file, then thought better of it). End result has 3 full steel threads, slightly >1 nylon thread, about the limit of what I would accept. It has a defined orientation, so I marked the side that should be visible, when installing.
Fitting was kind of clever. Very gently insert the bolt starter thread into the nut, then hold the derailer in my hand and squeeze so the inside corner clamps on the nut. There's enough give to 'thread' the cable in, straight-on.
Not much to look at I suppose. Had to use a longer M5, not the fancy Shimano one. I'm not deep into weighing things, but this is 3.5oz lighter than the parts bin derailer I have been using. Went on a test ride and it feels good, works fine, holds adjustment.
