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Deore BRM615
Outside piston is sticking in the 'out' position
I've helped the pistons reset with the gentle application of a cone spanner which will stop it rubbing for a few rides I expect.
It's the longer term fix I am after.
Worth a bleed? I flipping hate this job so thought I'd ask here first.
Obviously no rebuild option
Anything to clean pistons/pump out/in routine anyone can recommend?
I usually pump them both out as far as they'll go then clean them with brake cleaner. Tease/force them right back and repeat a few times until both of them are coming out equally. Seems to work ok
Thanks. Any particular cleaner?
I've got some spray car brake cleaner kicking about I assume with the Shimano system being oil based then it ought to be safe on the pistons. If not I probably have some silicone spray lube about the place.
I just use a drop of Shimano brake fluid and work the piston in and out a few times (while clamping the opposite piston).
I lubricate the pistons with hunters silicone lube, you can get it from plumbers merchant, it's for lubricate seals on waste water pipe.
All the above posters have shown that they don't understand how a hydraulic brake works.
The pistons do not move through the seals when you brake. What do you think would make them retract? The pistons move thanks to the flexibility of the seals, which deform under pressure than pull them back when they return to their normal shape. As the pads wear the pistone do slip slowly through the seals to take up the space. The pistons are a extremely tight fit in the seals, which are quite robust rubber.
If the piston isn't slipping though the seal enough and is getting "left behind", cleaning everything might work, otherwise take them apart and fit new seals.