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Never seen this before... my son’s ride-to-school bike, back brake has gone stiff, hardly any travel in the lever. I thought seized pistons, so cleaned and greased round them, gave it a bleed (loads of bubbles!).
Squeezed the lever after and it felt normal, but after a few more squeezes went back to being stiff. Works ok, just feels odd.
(Not sure if I described that very well - so the lever works fine, pulls in and returns ok, just feels kind of solid, like the pistons hardly move before contacting the disc. No feathering at all).
Any ideas?
How worn are the pads? Down to the metal?
Hardly worn looking really!
And does the same with just the yellow block in the caliper
I've got one out of half a dozen that does just this. Its quite an old one , early 615 id guess. No idea why, but it happened after a bleed IIRC. Not investigated too hard in case it reverts to variable lever travel like the others. It does its job, slows the bike down.
Yeah, but this one has the additional problem of causing a moaning child! 😉
Back brakes not right Dad, need a new bike...
This happened to me with a Formula brake which of course use DOT fluid and not Shimano's mineral oil. All that was needed to cure it was to open the calliper bleed nipple and let out a tiny amount of fluid, being careful not to let any air back in. If you have just bled it there may be too much fluid in the system and they use so little fluid overall that even a very small increase could lead to the problem you describe. On the other hand of course I could be completely wrong! However it is a very quick and easy thing to do to eliminate a possible.
Sounds like an overfilled system to me too. Or something is amiss in the lever.
Sounds like your piston in the master cylinder isn't returning properly, and masking the port that allows fluid to return into the reservoir.
Whats probably happened is the brakes have been bled with the lever adjust set close to the bar for small hands and the bleed has let too much fluid into the system.Try resetting the lever reach adjuster for max hand size and bleeding. Use the yellow bleeding blocks too.
Combination between BillOddie and coatsey's theories, methinks.
I re-bled the lever and it's better, still not completely right, but I'd be happy if my XTs worked like that. (ie. kid'll have to live with it 🙂 )