Bike had been left unused for a couple of months. When I went to ride it found the rear pads unuseable, no power and squealing like hell. Cleaned the rotor and inspected the calliper seeing no obvious signs of leakage. Changed the disc pads and all was fine. Bike has been left again for about 6 weeks and the same thing has happened, new pads now squealing and no power……Anyone have any ideas what is wrong? It is a Shimano XT disc BTW

Ta

Unfortunately, this sounds very like a leaking piston, which despite many people saying great things about them, is, in my experience, common with Shimano calipers. New calipers required.

R

If it the m785 model your referring to I can sympathise!
Its probably due to leaking around the banjo bolt where the hose is crimped or a piston. Could also be caused by the O ring in the banjo bolt not sitting properly, but reckon that’s quite unlikely.
I’ve got a set away at Maddison at the moment for a warranty repair/replacement as I had the same trouble as you. I fiddled, faffed, swore and finally gave up after multiple attempts to bleed/sort the brakes out.

Leaking from the piston killed my rear pads twice before I looked closer than just changing the pads
Only fix is a new caliper.

Thanks for the replies. It is a M775 caliper. Will take out pads, and replace with spacers and try to see if the pistons have a leak. Cant this be fixed?

If it is leaking from the piston then sadly put it in the bin
Shimano do not sell the spares. Only the bleed nipple is available I believe
But nothing else.

My rear m775 had a leaking piston and was contaminating my pads, new calliper or new brakes, I bought some hopes. Still have a complete front brake with a couple of spare pads if your interested.

I had the same thing with a leak from the hose connector on the caliper, so it’s not necessarily a piston leak. In my case it was fixed by changing the hose.
p.s. it was so small it wasn’t even visible as a leak, but if left for more than a few days contaminated the pads.

Me too- M775 leaked at about 15 months old. Now in bin and replaced with a cheap and cheerful M596 Deore caliper. Don’t realistically expect it to last any longer than the original.

Anyone who’s got a toasted caliper, can I have your old pad retention bolt pleeeaase?

Thanks all for the replies

Shindiggy… May be interested in your front M775 although sounds like I really only need the caliper. PM me and let me know what you are after. I will try and confirm where the leak is over the weekend.

I’ve had Shimano leaking caliper episodes

OR

Do you park this bike with the brakes next to the transmission on another bike? I’m pretty sure that’s what did it to mine twice before I sussed it and put them transmission to transmission before locking them up.

Got the same problem with the same brakes on the wife’s bike.
Driving me mad.