I've got two sets of Shimano M800 Saint brakes.
Set 1 I've had from new and they've been faultless. I've bled them repeatedly, changed the pads, and they've always been great.
Set 2 I bought second hand a while back. They were a bit dodgy to start with, but managed to sort out the front brake by baking the disc and pads and giving them a bleed.
The rear however has been nothing but trouble. Even after baking the pads and discs, there's a significant lack of power on the brake. One finger braking won't lock the wheel (and it's a struggle with two fingers). Leaving the bike for a week then taking it out and the brake has developed an awful squeal, which only goes away after ~30 seconds of dragging the rear brake on down a hill.
Any ideas what on earth is going on here? I'm almost at the point of taking them to my LBS to look at 8O.
Addendum: I've got a set of the same style XT brakes which work great. I've been considering swapping out parts bit by bit (e.g. swap over the XT caliper onto the Saint lever and hose) to try and identify any parts of the Saint brakeset that are 'bad'. Worth a go?
Nes pads and disks required I guess, they sound containinmated
Big road hill , drag the brake gradually harder and pedal against it, repeat a good few times. And burn the pads in and the gunk off. that and alternating full hard stops from speed
Just don't let the bike come to a stop for a while till the pads cool.
Shimano seem to grime up quite easily, doing this has brought back the brakes to their decent grab feel
You should be able to clean rotors very easily, no need to buy new. Pads on the other hand may hold oil so will need to be replaced.
My money is on leaking piston seals. This happened to me with SLX brakes and no matter what I did the squeel came back and the brake lost power. I traced it back to the piston seal leaking oil onto the pads. Got them refunded under warranty as you can't buy replacement seals and this is a recurring problem if you google.
If theres a lack of power, there is a possiblity of leaky seals. Had similar with a rear XT M765 caliper. After lots of bleeding I noticed it was slightly moist around one of the pistons, seal was weeping allowing fluid out and air in = lack of power.
Another vote for leaking piston seals. If you squirt water on them, and pump the lever, you'll see bubbles around the piston. The water on the ground will have a oil film on it too.
Thanks for the input everyone. I've suspected leaky seals but wasn't sure, but looks like there is a way to check. I'll have a look tonight.
Will I have any luck going for a warranty replacement? Given that they're an old model and second hand I wouldn't have thought I'd be in with a shout. Maybe a discount off a new set of 810s? 🙂