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Anyone tried to service some XTR M965 disc calipers? Mine have very sticky pistons. Is WD40 (other penetrating sprays are available) safe to use on them, after taking the pads out of course.
Dont use anything other than mineral oil for starters.
What I do once in a while with my shimano calipers is as follows.
Take wheel and pads out, then drip some mineral oil around both pistons and then carefully (slowly) pull the lever pushing the pistons out (not all the way, perhaps 3-4mm max). If one is a bit sticky, hold the opposite one in using a plastic tyre lever (something that wont damage it) and move the sticky one in and out repeatedly, wiping off any dirt that appears using a cotton bud and reapplying more mineral oil. Repeat until the piston is moving freely.
Then do the same on the other piston.
Once done, wipe up all traces of oil from around the pistons and caliper, reinstall pads and wheel and see how it goes.
Giving it a bleed after wouldn't go amiss either.
Will give that a go. Its the inside piston that keeps sticking. Means my brakes keep squeaking 🙁 Really irritating.