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Bought a set of used m785 brakes a while back from here and only just got round to trying them. Rear hose was tiny so replaced it with a BH90 hose kit. Trying to bleed the rear using the gravity method which ive used before with my other xt's but these won't bleed.
Yesterday i tried and ran 4 funnels full of fluid through them and it was not stop air, I gave up and just had another go at bleeding them. fluid is coming though now with no air bubbles, I nip up the bleed screw and remove the funnel and on pressing the lever there's no movement in the pistons as like there's not enough fluid in there.
Not sure if the the brakes had it or not? Anyone any ideas what the problem could be?
Thanks
I'd fill from the bottom up first, then bleed after.
Follow the Shimano instructions, if it doesn't work, follow them more closely.
They work every time, if you follow the instructions.
You don't say, but I'm assuming the lever does move and the pistons don't.
There will be air somewhere. Either that or fluid p1ssing everywhere.
Bleed them again, pump levers, keep caliper low and levers high, unbolt the caliper so it is definitely at the lowest point of the system. Basically you need to persuade the air to migrate up to the lever and then be replaced with fluid from the master cylinder in the lever, however you do that. e.g. look at this https://www.pinkbike.com/news/video-marshy-attempts-to-teach-greg-minnaar-how-to-bleed-brakes.html
Personally I'd split the caliper and pop out the pistons and seals. Clean the seal grooves, lubricate everything and reassemble. Easy job and quick job that will have it working like new.
Thanks guys , Yeah lever went to the bars  but pistons didn't move.
I have finally managed to bleed the things after nearly throwing them out. Tried yesterday pushing fluid up but nothing came through the funnel and went back to the gravity method which ive always used.
Just tried again now with the syringe pushing up, fluid was p1ssing everywhere but finally unblocked the blockage as a load of black gunk went into the funnel and now i can bleed them fine and the brakes feel good.
Is there resistance at the lever?
Follow the Shimano instructions, if it doesn’t work, follow them more closely.
They work every time, if you follow the instructions.
+1