[Closed] Whats up with my XT brakes?

JackHammer
This one?:

that was a very interesting and educational...thanks 😀

@alexh

Yeah I'm leaning towards the worn rotor/pads side of things now.

As far as my understanding of the servowave goes, it allows for wider piston spacing, therefore a bigger gap between pads and rotor so less "shhhhinnngg shhinng" from warped rotors (which was something I always used to get with avids).

This bigger gap is then accommodated for by the "servo" pivot or whatever which instigates more movement at the pistons for the initial lever pull travel (top the bite point).
So it would suggest that this "servo" part of the lever travel is tuned into the width of the rotors and pads, only varying a small amount (ie pad wear). When you add on rotor wear, pad wear and maybe misaligned pistons (not-centered) you get the lever having to go beyond this large movement zone to the "modulation" zone of the lever throw, where there's comparably little movement of the pistons and a spongey feel on initial pull.

As with the elixir brakes the reservoir on the shimanos may not hold enough fluid to push the pistons out far enough to self adjust to the wider spacing, so require a second pull to get the pistons and lever throw servo tuned bit to bite at the right time.

I am not an engineer so sorry for the terrible technical language.

Rotor and pad wear should have no effect on an open brake system - the whole point is that the pistons move out to compensate for the wear using fluid from the reservoir.

Well, mine have never worked like that. On both bikes, as the pad gets low, the throw to biting increases (it's slight, but enough to notice when my pads are low).

The only thing I changed on my bike, were the discs. It went from circa 8mm throw (on the lever) to the pads biting, to about 1mm throw.

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Get out!

years of happy Avid use here too.

What frustrates me is that shimano don't seem to be addressing the issue, which is obviously a big one as so many people are suffering the same/similar issues.

I wonder if it really is 'a big one' [problem] given the number of Shimano brakes out there and the fact that at least some of the issues seem to be down to user maintenance error? I'm not saying it's not annoying or unheard of, just that it may statistically be quite a small problem, even if it's a really annoying one if it happens to you.

Fwiw,, we have seven sets of Shimano hydraulic disc brakes on various bikes and they've all been hassle free. Which conversely doesn't mean there's not a problem, just that the internet tends to amplify frustrated voices. Maybe...

Well i've replaced everything but the rotor and caliper on my dodgy one, and there's a definite a lip from the spider arms to the pad contact strip. So i'll swap the rotor and put some fresh pads in it in the near future and see how it goes.

Well, mine have never worked like that. On both bikes, as the pad gets low, the throw to biting increases (it's slight, but enough to notice when my pads are low).

I know - I have a set that do this too - but this isn't a "feature" of the brakes. Its an indicator of a brake not working correctly for whatever reason.

This is my understanding of how an open brake system SHOULD work....

The caliper seal acts as the spring to return the slave piston to its original starting position after you pull the brake lever. But the seal is also designed to allow the the piston to move a little bit past the seal in the event of the piston moving further than a set distance (i.e. if the lever pulls all the way to the bar).

The result of this is... if you push the pistons all the way back into the caliper and then keep pulling the brake lever, the lever will travel all the way to the bars on the first few pulls but gradually the pistons will move outwards bit by bit until the pads contact the disc. At this point the lever should be biting at the correct point in the lever stroke and the pads should remain a set distance from the disc when the brake is not applied. The size of the gap between the pads and the disc is determined by how springy the caliper seal is (i.e. how far the seal can move outwards with the piston before the piston breaks away and slips past it).

This system is designed to cope with pad wear as the pistons will move out over time to compensate for the loss of pad material while always maintaining a set distance from the disc.

As the pistons move out over time, fluid from the reservoir flows out to compensate for the increased volume of the system...but this can only happen when the lever is not being pulled. When you pull the lever past a certain point the port to the reservoir is closed off in order to allow the brake to powerfully bite down on the disc.

interesting to note the similarities between this thread and that on cable discs the other day.

Ecky-Thump - Member

JackHammer
This one?:

I only had 10 mins last night to have a look at them, but simply following the 3 step process of setting the screw mentioned in that link has all but eliminated the problem I'm having with my XTs immediately - I'll have more time at the weekend to really look at them.

So the seal, which returns the piston also slides along the piston to account for wear? I wonder if mine are not sliding to account for this.

^^^ that's what is generally described as a "sticky piston" alexh.
Take out the pads and cycle the pistons in and out a bit (prizing back before they come out too far and the seal pops out of the end of the bore.

It's a good idea to clean any mud/braking dust off the piston sides before poking them back into the caliper as you'll introduce it into the fluid otherwise. Your enemy's toothbrush is a good tool for this.

I have this exact problem on my XT's M8000 bought on 17/12/15. After reading this thread I've decided to contact the Seller CRC. Here's a copy of my email.!!-----/

After 3 weeks of issues, regretfully i am having to email regarding a warranty issue.

I purchased the above brakes on 17/12/15, fitted a few days later I was experiencing an inconsistent brake feel, the brake bite point pumps up after initial use, especially on steep downhills, and vibrations, thinking it was the fact the rotors were not Shimano I then purchased full Shimano XT front and rear rotors from yourselves.

The initial bite point / pull of the lever is close to the bars (just how i like and set up) then subsequent quick pulls mean the next bite point is half as much away from the bar and this then returns to original pull once I've let off the brakes, say on the flat and then when I next pull the lever the whole things happens over again. There is no brake fade. Please note that when the yellow Blake bleed block in inserted this does not happen, the feel is perfect, it's only when installed on a rotor.

I have since fitted the Shimano rotors and adaptors and the problem continues, I have taken the brakes and bike to my local bike shop thinking the problem was air in the system, but like me they have no air and cannot solve the inconsistent feel, they even returned my money as they were unable to help.

The bike mechanic mentioned something about there being a warranty concern regarding these model of brakes and after further inspection on the Internet and forums I can confirm that this is true. Customers are experiencing the same problem, they have also done what I have done and bled the brakes many times hoping to cure the issue but have eventually contacted their supplier r.e warranty replacement.

I have never had an issue with Shimano goods nor any product from @@@ however I'm afraid to say that these Brakes must have a warranty issue. Not only is the issue frustrating it could also be potentially dangerous.

I'm emailing this evening in the hope to ask for some help and advice and hoping that you can contact your supplier to get them exchanged. Please find a screen print of my most recent purchases.

I'm not expecting a refund for the rotors or adaptor as there is no fault with these, but please can you help with these brakes.

Another job I'll add to the list! Thanks.

Just because no-one complains, doesn't mean all parachutes are perfect.

My M8000s were exhibiting the same issue. Tried multiple bleeds, fiddling with the bite point etc. Earlier today I took out the wheels and gently squeezed the lever a few times until the pads moved closer together (but not too close, obviously!). Put the wheels back in, re-aligned the calipers and the problem seems to have gone. Bite point consistent with no pump up. I'm going to reserve judgement until a proper trail ride in FoD on Saturday morning though.

Are people that are having problems mainly finding that it's the rear brake?
I've got a few sets of slx/xt/zee brakes. Some work perfect some not so much.
I have noticed though that all the front brakes work perfect and it's a couple of rears I have problems with.
I plan on swapping front and rear calipers around to see where the problem goes.
Don't think it's a bleeding problem I'm having as i've bled them all the same way.

Earlier today I took out the wheels and gently squeezed the lever a few times until the pads moved closer together (but not too close, obviously!). Put the wheels back in, re-aligned the calipers and the problem seems to have gone.

SSStu- Rear suggests it's a bleeding issue. Longer, more horizontal hose line will have be trickier to eliminate air from.

Drain system and bleed bottom up - preferably off the bike with caliber vertically below the master cylinder.

Just fitted my m8000's so will see how they go. Was hoping the new ones might be trouble free but the above reports don't give me confidence.... 😐

Hope to produce a powerful 2 pot brake

You mean the v2...

I didn't realise they still made those? Can't find them on the website? Had them on a dh bike several years ago much more simple to work on the pistons than 4 pots and More powerful.

Drain system and bleed bottom up - preferably off the bike with caliber vertically below the master cylinder.

I used to have this problem all the time with Formula Oro K24s. Easily solved by zip-tiing the levers back (i.e. 'on') to the bar in between rides.

This sorts the problem of too much lever travel for the first few braking episodes on a ride but I think the people reporting sudden brake failure mid-ride must have air in the line.

I've been following this thread because my back brake does exactly this. First pull, straight to the bar, then a quick extra one gets it working spot on until I release for more than a few seconds, then back to the bar again. If I do it off the bike I can see the pads going back for a few seconds after releasing the lever. I really don't think bleeding or adding extra fluid, or using thicker discs is the solution.

singlespeedstu I think you are right, but it doesn't explain why most people are having rear brake problems and not front. And if so why is it doing it? Would love to get to the bottom of it, I really do like thread brakes, apart from this. My wife's are spot on.

Well my FRONT SLX does this if that helps

My M8000s were exhibiting the same issue. Tried multiple bleeds, fiddling with the bite point etc. Earlier today I took out the wheels and gently squeezed the lever a few times until the pads moved closer together (but not too close, obviously!). Put the wheels back in, re-aligned the calipers and the problem seems to have gone. Bite point consistent with no pump up. I'm going to reserve judgement until a proper trail ride in FoD on Saturday morning though.

As said above, this only improves the brake for a short while, usually about 1 ride for me. The system seems incapable of self adjusting the pads to keep a consistent bite point.

my girlfriends Kona has the problem in the rear brake, I followed the XT Tech Video on "whispers"the MBR site, and it has helped a lot, although after reading the above posts i do think there is a case for warranty replacment as it is dangerous if you are not aware of it.

as it seams to be a rear brake issue mainly, has anyone tried bleeding the brakes with the bit point adjuster / lever throw dial all the way out to try and 'over fill' the system? would that help?.

again, being a mainly rear caliper issue, is there any millage in better hose's like goodridge or something similar?

This seems to happen to my brakes from time to time and, as folk have been saying, it's also my rear one which goes.

The issue always occurs after a very wet ride at Sherwood Pines....which is odd.

So, rear brake pads wear quicker than front ones, wet rides certainly wear them down a bit. Is Sherwood pines Sandy? This does all point towards the brakes not calibrating themselves for pad wear. Either the pistons aren't pushing past the point where they slip a bit on the seal, which I think is most likely. Or not enough extra fluid is getting pulled out of the reservoir, less likely as two quick pulls gets them working until the brake lever is released implying fluid is being pulled out of the reservoir, but then forced back in again by retracting pads

And me noticing the pads going back over the course of a few seconds could be explained by this as the seals are pulling the pistons back, but having to force the extra fluid back into the reservoir, which is going to take a bit of time, much like when you push the poisons back in to install new pads, there is always a bit of resistance.

So could it be bad quality control on the main piston seal?

Not sure if my understanding of the way they work is correct, or my descriptions make any sense, but...

So, rear brake pads wear quicker than front ones, wet rides certainly wear them down a bit. Is Sherwood pines Sandy? This does all point towards the brakes not calibrating themselves for pad wear. Either the pistons aren't pushing past the point where they slip a bit on the seal, which I think is most likely. Or not enough extra fluid is getting pulled out of the reservoir, less likely as two quick pulls gets them working until the brake lever is released implying fluid is being pulled out of the reservoir, but then forced back in again by retracting pads

And me noticing the pads going back over the course of a few seconds could be explained by this as the seals are pulling the pistons back, but having to force the extra fluid back into the reservoir, which is going to take a bit of time, much like when you push the poisons back in to install new pads, there is always a bit of resistance.

So could it be bad quality control on the main piston seal?

I agree that this is the most likely scenario
I bled my brakes for the 3rd time in succession yesterday evening - even though I don't believe there is air in the system - still exactly the same.

I also tried cleaning and greasing the pistons - while doing so I accidentally popped one all the way out. It seemed a little rougher than expected at the point the seal passes over it and discolored.

Does anyone know if its possible to get replacement pistons and/or seals - mine are xtr trail brakes?

I'm guessing not - this is the major advantage of Hope

You can, it just comes with a new caliper body too. 🙁

Someone on MTBR suggests that the latest XTR brakes are running the older white/cream (ceramic?) pistons. If you have ones with black pistons these are apparently known to have a (tolerance?) problem according to Shimano USA iirc.

Just as I thought 🙁
they are definately...

white/cream (ceramic?)

I don't have Shimano brakes and have no idea why I have just read this whole thread but I'm wondering if there is a common reason why this problem occurs.
I wonder if a short set of questions could throw up a theme.

Has the front brake been bled since new?
Has the rear brake been bled since new?
What fluid was used?
What rotors are being used?
What pads are being used?
Is the problem front and rear or both?

My thoughts are that this reply from from Shimano in the article linked above if true could be an influence.

"The rubber seals in the system have to be specifically designed to interact with a specific brake fluid. If you use a different fluid, the seals will interact differently. Specifically, when you put Magura fluid in Shimano brake, the lever feels spongy and the pad contact point changes because the square edge seal at the calliper is breaking free from the piston at a different time"

Regarding the rear seeming to be more problematic it may be that some frames with internal routing etc. mean that the calliper has to come off to facilitate hose routing and consequently requires bleeding or that front cables are generally about the right length and often don't need shortening but rears nearly always need shortening.
From experience bike shops just use car brake fluid in dot systems (even thought they often have bike branded fluid for sale on the shelf). I wonder how many use genuine Shimano mineral oil?

I wonder how many use genuine Shimano mineral oil?

I don't have a very high regard for bike shops but Id be very surprised if any were quite daft enough to use DOT fluid....and certainly not in all of the cases mentioned in this thread.

I wasn't saying they use dot fluid in mineral systems if you read what I said. I'm saying that I have seen them use car branded fluid in dot systems which is perfectly fine according to the manufacturers in the the article above who use dot fluid in their brakes.
I'm more posing the question of how many shops use genuine Shimano brand mineral fluid every time or do they use something cheaper?

OK but its not that as my little bottle says "Shimano" on it. Not that other mineral oil would behave any differently.

Also I use Motorcycle branded DOT fluid in my hope brakes
Why?
Cos its exactly the same and miles cheaper

How many shops use genuine Shimano brand mineral fluid every time I wonder, or do they use something cheaper?

Probably relatively unlikely as if they have to send them back under warranty and Madison/Shimano find non-shimano oil in them, they won't warranty them.

I have used Halfords/Citroen mineral oil in Shimano brakes before but now use Shimano.

The Halfords/Citroen stuff is noticeably more viscous.

More viscous = harder to bleed.

Probably relatively unlikely as if they have to send them back under warranty and Madison/Shimano find non-shimano oil in them, they won't warranty them.

Good point.

The brakes can have the same issue even if never bled or worked on in any way.

Seem to have achieved a decent bleed on my dodgy front Zee by pumping lever repeatedly and sealing top cap up quickly, but it still squeals like hell and lacks power.

Likely culprit for this is sticky pistons I think. Retailer has agreed to take them back anyway though.

Is this issue more prevalent in the M8000 XT brakes or just Shimano in general? I was thinking of buying some M675 SLX brakes due to how cheap they are now but think I might hold fire considering the amount of horror stories in this thread so far...

I have had a range of shimano brakes do this. Always much worse on the rear. Normally for me it has indicated that the piston seals have started leaking - I have had 1 set of deores and 1 xt warrantied (front and back) for this reason.

The double pull thing is happening at the moment but unusually there [u]doesn't[/u] seem to be any signs of a leak. I had just bought a new calliper rather than being without a bike for a few weeks but I am concerned that I will replace the calliper and find it has made no difference.

FYI I can bleed the working front perfectly every time but the rear rarely stays good for more than a ride or two even if bled hanging from the bars only.

If the problem more frequently occurs in the rear brake then presumably the thing to look for is any difference between front and rear brake. The biggest (only?) difference is the length / angle of the brake hoses - the front being shorter and more vertical. Does anyone else clamp their bike in the frame so the rear hose is as near vertical as possible before bleeding? The few times I've done a bleed with the Epic Bleed kit I do this and give the hose a good tapping all the way up. I don't know if that would help - but probably worth a try and it will do no harm.

The truth is there is no technique or trick for bleeding Shimano brakes that people are missing. In fact lots of people are going way beyond what is required to ensure a great bleed. Sadly Shimano brakes are flawed by having this major issue along with poor bite point control and not being small part fixable. You would think they would have sorted all this out by now.

I agree that bleeding isn't the problem. Air in a brake system just doesn't cause this very specific problem. People are getting them working after a bleed, but it normally involves pushing the pistons to where they should be for the current disc thickness/pad wear and over filling the system, which will work until the pads wear down a tiny bit, then back to square one, the pistons aren't realigning themselves.

Why it is more common on the back than the front who knows. Maybe because they get hotter which pushes fluid out of the system back into the reservoir, which can't then get back into the system properly, doesn't quite seem right because the pads haven't gone any further back. Or maybe because the pads wear quicker it happens more often so is more obvious?

New pads and thicker rotors are just temporarily hiding the problem imho.

Am about to hit 'buy' on a set of Hope X2s, that should solve the problem! 😆

Pads wear quicker on the front though.

[quote=reev ]Is this issue more prevalent in the M8000 XT brakes or just Shimano in general? I was thinking of buying some M675 SLX brakes due to how cheap they are now but think I might hold fire considering the amount of horror stories in this thread so far...
As far as I know, these issues only seems to have started with the 785/985 brakes and are now continuing with the 8000/9000 range.

I can't believe what a minefield I opened up with this thread. I was expecting quite a straight forward answer, not the consensus that this is a widespread problem with no real solution and nobody really knowing exactly what the cause is!!

I'm sending mine back to CRC to see what they say or do and if there's any useful information from this ill post an update.

^edward2000

If only someone from Shimano read this! Madison have been good to take a look at mine and will let you know what they say. The only way they might acknowledge there is an issue (and with this many people having issues i cant believe its just incompentence of bleeding) is if everyone sends them back. I am changing as i just dont feel safe using them currently so I'll see what they say...

In worse conditions (where more mud/grit is being thrown onto the rear disc) or when you're brake dragging rear pads often wear quicker than the front. When it's drier and/or you're braking with better technique the reverse tends to be the case. Also depends on your tyres and rear suspension.

Having exactly same problem as well.

Is this only happening on the "UK" set up ? or a there riders on the continent moaning about their front brakes.. zut alors zis shimano est merde etc etc

Pads wear quicker on the front though.

Depends where you ride and in what weather. I go through rear pads 3x faster than fronts due to a lot of wet riding (puddles as well as in the rain) kicking up the grit and sand onto the rear caliper and disc chewing up the pad. The front doesn't get anywhere near as much crap on it so the pads last a lot longer. In winter I can still get away running softer pads up front (uberbike semi-metallics are my go-to, nearly as good as the Rahox ones but significantly cheaper!) whereas I need to go to sintered on the rear to not have to change then every ride or so. Go through rear discs faster too. Been the same on my Shimano and Hope brakes.

I currently have 3 sets of Shimano brakes (2x Deore, 1 XT) and they all work fine. I did have to bleed the rear XT a few times to get all the air out of it initially (on my 5 so hose off to fit) and found standing the bike upright really helped. One thing I have noticed is that Shimano pads are noticeably thicker than aftermarket ones, could this be a problem? I found the OE ones stopped working once they'd worn down to the end of the chamfered part of the pad so you're not getting any more useable pad depth but maybe the caliper is set up to use thicker pads and this is causing issues? If it is maybe fitting some of the aftermarket fins would space the pistons out further, sort of simulating the thickness of OE pads.

If the XT's show any sign of playing up I will be going back to Hope. Only switched to XT as A: my rear Hope was old and needed upgrading to keep up with the front and B: I was fed up of constantly having the wrong spare pads in my pack (Shimano when riding the bike with Hope and vice versa). It was cheaper to switch one bike from Hope to Shimano (actually made cash 😀 ) than put Hope on the other two bikes!

After reading all this I'm keeping my fingers crossed as we haven't experienced any of the problems and are running eight sets between us.

Well, today I went to swap my rear pads and noticed a stuck piston. My attempts to press it back in resulted in a cracked, leaking piston.

Just got a new 800 caliper and lever from lbs as I need it for tomorrow.

May explain the poor performance on that set.

I can't believe what a minefield I opened up with this thread. I was expecting quite a straight forward answer, not the consensus that this is a widespread problem with no real solution and nobody really knowing exactly what the cause is!!

Errr, perspective required, please. I haven't bothered to count the number of individuals who have posted on this thread, but let's take the number at the top of each page, which says 68. Now, before starting a zombie shimano brakes apocalypse, I wonder how many units have been manufactured in the last 4 years or so? Hundreds of thousands? In percentage terms, possibly acceptably small enough to warranty.

Of course, there is the possibility of death, at which point my perspective plea falls somewhat short and I just hope the tabloids don't get to hear about this epidemic.

Internet eh? 😉

P.S. Stealth edit 😉

OK but its not that as my little bottle says "Shimano" on it. Not that other mineral oil would behave any differently.

Shimano brakes HAVE to have shimano fluid in them. It's a propriety fluid. All 'mineral' fluids are not the same. It affects the seal performance.

Just to add some more food for thought, mine started to do it when I took the wheel out and put the bike in the car on its side.When I put the wheel back in I had to pull the lever a few time before it went hard, which is fairly normal as the piston could have been moved back whilst taking the wheel out. But the other day on very bumpy down hill the lever went to the bar, I did the run again 3 times and everytime on teh same drop it went to the bar!

Maybe it has something to do with the fuild level in the lever. Anyway I have now bleed it and cleaned the pistons, we will see what happens.

Hi all, I had the same issue and sent them back to the online retailer who in turn sent them back to Madison/shimano. the seals on the piston in the lever were dodgy so would release the brake pressure a few seconds after pulling the lever.

They were replaced within two weeks, so I think Madison/shimano know the brakes are poorly manufactured.

The term mineral oil is like engine oil. Loads of different component mixtures, for example cyclo mineral oil is definitely thicker than shimano fluid. In that article on the first page im pretty sure there's a table with a boil point temps on it and shimano claim their BP is a lot high than bog standard mineral oil or even royal blood.

Is it just this/last years Shimano brakes that do this?

Are deore brakes problematic?

I have some Avids that I was going to swap for Shimano...

I have my Hope X2's for sale because I wanted to buy some M8000's.
I've never had a bad set of Shimanos and I've had few sets of Deore/Slx.
Think I'll keep my Hopes now though because aside from the length or shape of the lever they're ok for me and my riding.

I have SLX and no issues, the XTs are not the same. For all those that insist on saying it must be the bleed etc, do be brief - i do nothing different between the slx and xt yet the XTs are so inconsistent they are dangerous. They have gone back to Madison. The latest mbr also refers to inconsistent bite point for a set of XTRs, something is wrong somewhere.

I've had a few sets of Shimano brakes and have generally found it easier to get a good bleed out of my Deore's over the posher ones. My XT's were powerful but I was never ever able to get a good solid lever feel and not where the shop I bought them from. My Zee's are easy to get set up well and seem consistent as we're both pars of Deore brakes that I had. My current XTR's may well be going back because they were pretty inconsistent on Saturday.

I think the new bleed process is more of a ball ache than it was on the early Shimano brakes. They were so easy to bleed and my original Saint brakes always felt great.

How many people are getting filthy black contaminated mineral oil out when they bleed?
When I have had this, it's usually coincided with the onset of inconsistent lever feel.
I can only speculate that this is from a seal that's deteriorated.
As it's evident at the lever end, I suspect it's the piston seal in the lever.

How many people are getting filthy black contaminated mineral oil out when they bleed?
When I have had this, it's usually coincided with the onset of inconsistent lever feel.
I can only speculate that this is from a seal that's deteriorated.
As it's evident at the lever end, I suspect it's the piston seal in the lever.

Yep - totally black after just a few weeks - although I'm voting for caliper seal

sorry to resurrect this thread, but after boldly claiming mine only do this when the pads are soon to die, the rear has been doing on newish pads on every ride for the past couple of weeks, creating a near death moment at wharncliffe today.

the consensus seemed to be that it was mainly a rear bake problem and likely due to the pistons not auto adjusting due to the seals. has anyone swapped a previously dodgy rear caliper with a working fine front caliper on their bike to see if it is a rear specific or a dodgy unit issue?

just trying to eliminate possibilities before i buy a new caliper (will do my usual overfill bleed first, but as that what was done last time not holding out much hope)

Don't know, but that would certainly narrow it down to lever or caliper sofaboy, 2 year warranty you know?

Don't know, but that would certainly narrow it down to lever or caliper sofaboy, 2 year warranty you know?

weren't bought as a complete set. currently saint levers on zee calipers (both under 2 years old) as smashed up the original zee lever assembly in a crash. not sure they would warranty a hyrbid set up, further complicated as bought from different online retailers. frustratingly i can't remember if the original full zee set up suffered from the same issue

very keen to sort out as today was very close to a face tree interface

I have been meaning to swap my front and rear calipers round to see if that moves the problem to the front, but haven't had a chance yet. I have also been meaning to try and send the back off for a warranty job, but that would leave me without a brake, which, as bad as the brake is, it's better than nothing. I could borrow my wife's back brake (xt working fine) but she might notice.

I did try over filling the system, which was fine for a while, but muddy sandy riding meant it wasn't long before enough pad had worn down to bring me back to square one again.

What a pain this all is.

tombon - Member
I have been meaning to swap my front and rear calipers round to see if that moves the problem to the front, but haven't had a chance yet.

if you do, let us know how you get on. i was going to do it myself, but the waters have been muddied by having a hybrid set up (saint levers, zee calipers) and i can't remember what the original set up (zee's at each end of the hose) was like

I've had a set warranted full of green Citroen mineral oil.

Fed up with my rear XT and dropping wheel out to pump pistons out to allow for pad wear! Tried bleeding but still comes back. Just ordered Hope E4s last night!

So far, fingers crossed, my new XT M8000's have been rock solid. Only one ride on them mind...

I had to shorten both font and rear hoses, pumped the pistons out before I did it.
Currently very good and solid but we'll see innit.

For what its worth i have just blead up the rear brake on a Kona process (third time lucky)and seem to have got a much better lever, I put the bike in a upright position so that the lever is at the top and caliper directly below,then i fitted a rockshok blead kit syringe (with o ring) into the lever/resevoir, Yes they fit!,After a while,and by tapping on the hose and moving the lever up and down on the bar small bubbles started to flow into the syringe followed by a bigger one.The lever felt much better straight away,having the rubber O ring on the resevoir is key here as its a visual guide to releasing trapped air.

Try a bit of logic. If it is mostly a problem with rear brakes then you can eliminate anything which front and rear brakes have in common otherwise it would effect both equally. As far as I understand it most of the equipment (seals etc) front and rear is the same. Do rear brakes get more crap and contaminants than front? Possibly but is that enough to account for the difference frequency of rear brake compared to front. It seems to me that the biggest difference is in the length of the hoses and, if brakes are bled in situ, the more horizontal run of the rear compared to the more vertical run of the front and maybe the orientation of the calliper. So orienting the bike so the rear hose is as vertical as possible (or removing to do the same) and giving it all a good tapping is likely to be a good plan. I've never had a problem with XT on two bikes doing this.

I had some XT M8000s. My front was worse than the rear - even from new before hoses were shortened. I bled about 5 times (with Shimano oil) including leaving overnight with lever tied back to bar etc...none of it worked. Have older shimano's on our other bikes which have been bulletproof. Madison warrantied...got a refund ... now have Hopes which are spot on.
Shame...been Shimano fan for over 20 years...hey ho.