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The recessed pivot nut for my front brake calliper (no. 4 in this diagram) has seized inside the fork.

I've managed to remove the brake calliper itself by unscrewing it from the front, but the nut is stuck so tightly that I'm worried I'll round off the socket if I try to extract it with a hex key. I've tried dousing the assembly in GT-85 but it doesn't seem to be helping.

Someone suggested screwing an M6 bolt in from the front and knocking it through with a hammer, but I'm not sure how hard I can safely hit it (my careful attempts so far haven't worked).

Am I likely to damage a carbon fork by doing this?

  • Got to ask. Why do yo need it out? – paparazzo Nov 26 '14 at 14:20
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    @Blam So that I can tighten the calliper properly; at the moment it can rotate slightly and tends to de-centre itself from the rim, despite repeated adjustments of the set-screw. – Will Vousden Nov 26 '14 at 14:25
  • If the recessed pivot nut is rotating slightly a new one might not fix it. More days of penetrating oil is probably not going go fix it a carbon does not rust. – paparazzo Nov 26 '14 at 14:38
  • @Blam The pivot nut isn't rotating. I meant that, since the calliper has to be aligned in a certain direction, I can't fully tighten it against the nut (the nut is positioned such that if I did, the calliper would be pointing the wrong way). I therefore have to leave it not-quite-tight in the nut. If I could release the nut, then I could hold the calliper in the correct orientation while tightening the nut instead. – Will Vousden Nov 26 '14 at 14:43
  • The carbon doesn't rust, but the nut itself is steel I think, so there might still be hope... – Will Vousden Nov 26 '14 at 14:44
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Please don't hammer it from the front. You risk rotating the nut and completely jamming it in the carbon.

Keep at it for a few days with penetrating oil. If that doesn't help:

Try to remove the nut by pulling it out from the rear. I would suggest finding out what size bolt will fit through the entire nut (perhaps M4). Get a long bolt or piece of threaded rod in this size and slide it through the stuck nut. On the front side, thread on two nuts and a washer (the washer goes between the nuts and the stuck nut).Screw both nuts tightly together.

On the rear side, place a small plate of (ply)wood with a 5mm hole in it. Make sure the block is shaped such that it comfortably rests on the rear of the fork legs/fork crown. Take some time to shape the wood, depending on your fork geometry to avoid any damage.

Thread a washer and nut onto the wood block, and thread on two nuts at the end of the rod again. Use a wrench to hold the the nut on the wood block, and another wrench to move the two rear nuts to pull out the whole assembly, including your stuck nut.

  • Thanks – I've ordered some better penetrating oil than GT-85 so I'll try that first. – Will Vousden Nov 26 '14 at 14:36
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The nut is most likely suffering from galvanic corrosion in which case penetrating oil won't work because penetrating oil does nothing to break the chemical bond holding the two parts together. Instead of penetrating oil you can try a mild acid (think lemon juice or vinegar) which might help eat away at the bonds without damaging the finish on your fork. The wood block method descried by biker12 is the safest solution.

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