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Was bleeding my brakes last night after returning from a trip to the Alps and noticed a strange issue with my rear XT lever. I had done an initial gravity bleed, but then just to check there was no air left in the calliper I was pressurising the system by squeezing the lever and then undoing the calliper bleed nipple.
However strangely, each time I did this the lever then refused to pump up again (with the nipple closed). Subsequent pulls seemed to move the pistons slightly, but the lever came back to the bar. It was like the lever wasn't pulling in fluid from the bleed bucket. The only solution I could find was to quickly flick the lever and it would then start to pump up again.
I had previously done the same technique with the front brake and had no problems at all. Does it sound like there's something wrong with the lever? The reason I ask is I have a spare, and was wondering if it's worth swapping them over now while I have the wheels out etc.
Most likely, the piston is just sticking in the master cylinder. The piston has to return all the way back so that the transfer port between the reservoir and master cylinder opens. If it sticks, fluid cannot transfer into the master cylinder and you will have exactly those symptoms.
I had done an initial gravity bleed
when was the last time you did a full bleed?
thols
Most likely, the piston is just sticking in the master cylinder. The piston has to return all the way back so that the transfer port between the reservoir and master cylinder opens. If it sticks, fluid cannot transfer into the master cylinder and you will have exactly those symptoms.
Exactly this but I've only ever seen this happen by people who don't do regular full bleeds.
I had a mate decided to do it a couple of months ago day before a race... asked me to come over and the oil coming out was not only black but full of clumps of dirt...
Sadly its a rather time intensive fix...
Full bleed was probably this time last year, and the bike didn't see much use over winter. The oil that came out was fairly dark, certainly not too bad though.
So, do we think it's worth changing the lever with my spare (new)? Or is this something I can fix relatively easy?
So, do we think it’s worth changing the lever with my spare (new)? Or is this something I can fix relatively easy?
It's a finicky disassemble and taking the master cylinder out... you can use any shimano lever compatible with your shifter mount. If it was me I'd swap the spare on first then set about disassembling
Hmm, just went back and checked - the issue seems to occur when the lever is fully pulled (back to the bars). You're right in that the piston doesn't fully return in this case. Pushing the lever forward seems to help it come back.
What potential issues are there if I leave it? Guessing the lever is never likely to be fully pulled due to pads being in place?
If I did swap levers would I be ok to keep the olive etc on the hose, or do I need to cut and add a new olive/barb?
What potential issues are there if I leave it? Guessing the lever is never likely to be fully pulled due to pads being in place?
It will get worse and stick in place... possibly less serious with the rear than front ??
If I did swap levers would I be ok to keep the olive etc on the hose, or do I need to cut and add a new olive/barb?
Can't really say unless I saw it. You often can especially once... it depends how much the olive is squashed... a decent guide is how many screw threads are left on the tighting bolt thingy that pushes the olive and barb in but ultimately you need to see the olive and check its not too squashed/deformed (sort of thing I would have a spare ready just in case)
Dismantled the lever last night and you guys were right, the piston is a little sticky so will replace with the new one.
Discovered something a little odd though - there was a slight difference between the two levers. The old one had a completely metal port interface (where the barb connects to the lever body), however the other one seems to have a piece of plastic in there with a smaller diameter hole for the fluid to pass through.
The levers are about the same age, one was a replacement for the other while being warrantied for a bad olive fitting. The only difference between them is one was from a Shimano pre fluid filled set, and the other was just the lever in the box. It was the lever from the pre fluid filled set which had the piece of plastic in there.