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This may have been covered before so apologies if it has, I did a search with no luck.
Last 3 or 4 rides, the bite point on my rear XT brake has got closer and closer to the bar as the rides gone on. First couple of times I could pump the lever and reduce travel momentarily, so figured it needed a bleed.
I was lazy and carried out the Epic Bleed 5 minute bleed which seemed to do the trick only for the lever to get closer and closer to the bar during the next rides.
So last weekend, I gave the caliper a good clean, lubed the pistons with some Mineral Oil and bleed it properly. Got a bit of air out at the lever, but once back together the lever pulled to the bar with no bite. So I pumped the piston out a bit and did the Epic Bleed 5 minute trick again and got quite a bit of air out.
Went out again last night, and same issue but pumping the lever made no difference. I’m beginning to think that maybe the pistons aren’t balancing themselves taking into account pad wear? Is this a possibility? Or am I just shit at bleeding brakes??
Oh, and sorry for the wall of text 🙄
Have you tried taking the wheel out, carefully pumping the brake once or twice then replacing the wheel. Should set the pads bit nearer to the rotor. Worked when i had the same issue with mine.
I have, but the issue returns as I continue to ride.
Are there any leaks around the hose at either end? I remember hearing reports of the banjo not being crimped on that well on some of the older M785's, or are you running the M8000's or whatever the new ones are called?
You've got air in the system or a leak.
Much has been written about the easy bleeding of Shimano by Avid haters, but there's a one liner in the destructions that come with the Shimano funnel.
If the brake is persistently turning up air and you can't quire get it right and are sure it's leak free... Open the hose up and drain all the fluid and start again from scratch as if you'd just fitted brand new hose. Open the bite screw while you do this. Should sort it although it's a bit extreme. Brake off the bike and hanging vertically with caliper at top may help too. There are some very hard to shift air traps in ServoWave it seems.
Thanks for the suggestions, I'll look for a leak over the next couple of days. Failing that I'll try and bleed again and if that doesn't work I'll drain the system.
Sometimes the seal in the lever deteriorates resulting in the piston not returning fully, which can block the ports between cylinder and its reservoir.
I've seen this twice on M785 xt brakes.
From personal experience, the indicators appear to be:
1. lever doesn't return to full extent of travel on release
2. resistance (or inability) to bleeding "bottom-up"
3. black seal residue contaminant visible in the fluid at the lever end
Remedy: New lever assy (seals not replaceable)
How worn are your pads?
I have noticed that if the pads are getting low this will start happening on all of the shimano brakes I have (2 x sets XT / 1 x XTR / 1 x saint). I use this as the indicator to change the pads, rather than waiting for them to be completely gone...