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Fitted some used Deore hyd brakes (not sure which model number) to my wifes bike a couple of years ago. She's not used it for a while and when I checked it over on Saturday the rear brake was not working at all.
Checked the resevoir and it was almost empty with some blackish stuff in the bottom.
Filled the resevoir and tried bleeding it but oil is not really being pushed through the hose and lever has full travel and little resistance. Fitted a syringe to the caliper and tried pulling oil through but not much came through.
I'm guessing that a seal has died and fallen apart into the hose. If so I believe there's little you can do in the way of servicing, so is the brake dead?
Try filling a syringe with mineral fluid and pushing it from the caliper to the lever. Is there any evidence of where the fluid had leaked from?
Like Bigyinn said, try pumping oil through from the caliper end.
Also, make sure the pistons aren't stuck in their bores. Take out the pads and lever them with the end of a ring spanner to check they're moving.
Check the hose connections at both the caliper and lever ends for leaks.
If you can't get 'em going don't worry. Just buy a new brake from Rosebikes and stick your old one on Ebay.
Pistons seized.... can't even shift them with compressed air. New brake time I think.
Ae Deore front and rear calipers the same?... think I've got a spare front brake somewhere.
Try giving the pitsons a good soaking in mineral oil for a couple of days. Is there any obvious signs of corrosion on the piston??
You should be able to disassemble the caliper by undoing the two halves of the caliper and bunging them in a pot with fluid in it?
If you can fill the hose with fluid to the lever, you may be able to get them moving then.
Calipers should be the same.
Hoses are different lengths and levers left/right but easy enough to swap over. 🙂
If the calipers are International Standard (IS) then they will be different front and rear, but if they are Post Mount (PM) they will be identical.
If you put a front IS caliper on the rear you will need a +20mm adaptor to get it to fit.