My caliper rotor push oil back in the STI. All of the sudden mineral oil started leaking.

Do you know SKU of this part?

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  • 1
    If you lift up the rubber "skirt" around the handlebar clamp, there will be a part number embossed into the plastic. This will be the part number for the whole shifter, probably something of the format "ST-7100" Please find that and then we can find maintenance manuals for this specific item. I'm guessing it will be a "ST-7020R" – Criggie Feb 14 at 8:13
  • Also - have you used anything but mineral oil in this brake ? – Criggie Feb 14 at 8:22
  • 2
    Did you try to re-assemble and re-bleed the brakes? Master cylinder should not leak when pistons are fully retracted. The diaphragm from the second photo looks OK and I have hard time imaging how extra pressure would damage it. This is not something I personally experienced, but maybe the system simply had too much brake fluid in it. – Klaster_1 Feb 14 at 8:41
  • @Klaster_1 You can pop them with egregious overfilling, but yea, that doesn’t look to be the case here. – MaplePanda Feb 14 at 8:44
  • The rubber bladder got a hole by resetting the pistons. And that sucks its a super sensitive part of the lever and it's not w replaceable. – Romualdo Ducon Feb 17 at 12:09

According to the ST-7020R exploded diagram at https://dassets.shimano.com/content/dam/global/cg1SHICCycling/final/ev/ev/EV-ST-R7020-4341C.pdf

That part doesn't exist as a removable part, hence why you need to confirm your exact shifter part number.

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For completeness - the dealer manual is at https://si.shimano.com/api/publish/storage/pdf/en/dm/RADBR01/DM-RADBR01-07-ENG.pdf and a browse through shows no mention of removing that plate.


The sad part is. That part is not replaceable. Ots not that tough when you push ur piston. That reservoir will pop and mineral oil start leaking.. i believe that it should be a replaceable. No information what so ever you will need to replace the whole shifter itself

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