XT M8000 Brakes 'pumping up' on descents

udi

udi

swiss cheese
These are actual problems with Shimano brakes that have existed for a long time now, it's good to see that official sources are finally calling them out on it.

It's a shame that the new crop haven't fixed it, and by the sounds made things even worse.

Can only hope that the new Saint/Zee lineups see a substantial internal redesign but it seems unlikely given the poor effort with M8000.
 
single-pivot

single-pivot

Likes Dirt
brakes

I am having same trouble with set zee brakes, 2015 they are woeful symptoms even after LBS bleeding and another go .
lever goes straight to bar first pull then pump up ?
 
big dan

big dan

Likes Dirt
xt brakes agghhhhhh

So, mine are doing this as well. bite point seems to be fine and then all of a sudden changes, mostly during rough sections but not necessarily in sections of prolonged braking. Have bled them twice now and it doesn't seem to improve them at all.

Purchased as part of a groupset from wiggle so i suspect it would be a PITA to send back.
 
wkkie

wkkie

It's Not Easy Being Green
big dan said:
So, mine are doing this as well. bite point seems to be fine and then all of a sudden changes, mostly during rough sections but not necessarily in sections of prolonged braking. Have bled them twice now and it doesn't seem to improve them at all.

Purchased as part of a groupset from wiggle so i suspect it would be a PITA to send back.
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Wiggle have local returns so shoot them an email, shouldn't be too much trouble....
 
wkkie

wkkie

It's Not Easy Being Green
northvanguy said:
Mine were warrantied by CRC.... 8 weeks without brakes though and i was on the verge of snapping with the delays
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Did you get a new set of M8000s? If so was there any difference in the calipers? I think I remember hearing something about that somewhere....
 
carpetrunner

carpetrunner

Likes Dirt
new 9020's - all good!

Just put some new 9020's on the '09 spesh #enduro
Old school external cabling so just bolt on, straight out of the box, with the factory bleed.

Only one short-ish test ride - through the Cascades - they were fantastic!
I tried pumping and all sorts of shenanigans and the bite point was steady.

Shimano must have fixed it?

- carpetrunner
 
The Duckmeister

The Duckmeister

Has a juicy midrange
It's been suggested through the media traps that, thanks to Shimano's trickle-down process, the issues have been resolved with M7000, and the fixes incorporated as a running change to M8000 & M9000 brakes.

Now, I have a supposition as the the issue, and it goes like this. I suspect the issue to not be hydraulic, but mechanical. Which is why repeated bleeding doesn't change anything, because it can't. What I suspect is a return spring imbalance between caliper and lever, possibly the resulot of too much friction in the pistons, poor oil flow through the caliper or just plain not enough spring force in the piston seals to retract them fast enough.

It goes like this: when you're off the brakes for any length of time, either when the bike is parked or you're on an open bit of trail, the pistons have time to retract fully. When you grab the brake, you get a long stroke. But when you release the lever, the return spring on the master piston pushes the lever back nicely, but the pistons in the caliper can't push the fluid back up into the master cylinder at the same rate, so the master cylinder recharges with fluid from the reservoir instead. So when you next grab the brake, if it's not that long after the previous grab, you've got a much shorter contact stroke.
 
link1896

link1896

Mr Greenfield
The Duckmeister said:
It's been suggested through the media traps that, thanks to Shimano's trickle-down process, the issues have been resolved with M7000, and the fixes incorporated as a running change to M8000 & M9000 brakes.

Now, I have a supposition as the the issue, and it goes like this. I suspect the issue to not be hydraulic, but mechanical. Which is why repeated bleeding doesn't change anything, because it can't. What I suspect is a return spring imbalance between caliper and lever, possibly the resulot of too much friction in the pistons, poor oil flow through the caliper or just plain not enough spring force in the piston seals to retract them fast enough.

It goes like this: when you're off the brakes for any length of time, either when the bike is parked or you're on an open bit of trail, the pistons have time to retract fully. When you grab the brake, you get a long stroke. But when you release the lever, the return spring on the master piston pushes the lever back nicely, but the pistons in the caliper can't push the fluid back up into the master cylinder at the same rate, so the master cylinder recharges with fluid from the reservoir instead. So when you next grab the brake, if it's not that long after the previous grab, you've got a much shorter contact stroke.
Click to expand...
Or the redesign has moved the port between master cylinder and reservoir further up the stroke (towards the resting position) to guarantee calliper piston retraction. Time for you to pull both variants apart.
 
S

slimjim1

Fat boomers cloggin' ma leaderboard
Just ordered a set of SLX M675 as a replacement. Thought about Guides, lusted after some Hopes, in the end went for the tried and true. Will mate up perfect with the ice-tech rotors and already have some shimano pads as spares.

Wanted the m785 XT but were unavailable on CRC. Meh, the only difference is the useless free stroke adjust and the better pad retaining clips, which I will get my hands on anyway.

I'll probably seek a warranty claim on the XT M8000. Then I will likely flog them off.
 
S

slimjim1

Fat boomers cloggin' ma leaderboard
Cheers Twelve, yea no matching set unfortunately. Same with CRC, had stock but was either wrong colour/wrong side to get the matching set.

I can't believe the M8000 is the most popular brake on CRC but you can get the whole SLX set cheaper...even putting aside the pump issue the performance differences are minuscule.
 
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W

will2

Likes Dirt
M9020's here.

Got a new set this week, I regularly get mine hot long steep descents of a few minutes or so.
Will see how they fair over the next few.
 
Tubeless

Tubeless

Likes Bikes and Dirt
slimjim1 said:
Cheers Twelve, yea no matching set unfortunately. Same with CRC, had stock but was either wrong colour/wrong side to get the matching set.

I can't believe the M8000 is the most popular brake on CRC but you can get the whole SLX set cheaper...even putting aside the pump issue the performance differences are minuscule.
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Same with all the online stores I've looked at - only odds n sods are left over.
 
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