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View Full Version : How bad is too bad for a brake piston


matthewb77
18th October 2021, 21:27
I have the piston out of a front brake for a 1980ish honda CB250rs from a wrecker. It appears to have been buried at some point in its life as it was full (even behind the piston) of dirt sand etc. The piston is a bit pitted from where it was sitting in the rubber seal. See the worst of the pitting:
https://i.ibb.co/k4B27mx/IMG-20211018-181748.jpg
https://i.ibb.co/1vyyDWs/IMG-20211018-181804.jpg

Does this look serviceable? I have a CB250N caliper in a bit better nick (not technically mine but close enough) that I could potentially scavenge a piston from, assuming they're the same size? Would rather not have to go through the hassle though.

Anyone know how I can tell if the rubber ring piston seal still alright? I can feel a bit of a ridge when running my finger up the inside of the piston, passing over the seal.
Does filling the pits with superglue work on brake pistons, like you can do with stanchions?

thanks
F5 Dave
19th October 2021, 06:09
Clean carefully with scotchbrite. What lives outside the seal sweep area is not so important. What is real critical is what the bore seal will rub against in action. The outer dust seal is for dust, the bore deal is the square one that must be a good working seal. Those big pits look like they are too low to get into that range. But mock it up with no seal in place, new or old pads, with a sharpie mark how much sweep the piston will cover.

If the pits will travel over the seal then I'd buy new. Try weemoto maybe or of course anaconda.
Hugo Nougo
19th October 2021, 20:46
it's fucked, don't piss around get a new replacement, search originals part number, and work from there.

https://www.ebay.com.au/itm/165005975363
FJRider
19th October 2021, 21:11
... If the pits will travel over the seal then I'd buy new. Try weemoto maybe or of course anaconda.

If ... is not the issue. Just will (0r when) they might. Could have issues ... at a later stage of normal use and wear .... ??

Yes. No ... or maybe .. ??
F5 Dave
20th October 2021, 06:35
. . . But mock it up with no seal in place, new or old pads, with a sharpie mark how much sweep the piston will cover. . . .
Read the post.