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  1. #1
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    Uneven pad wear on Shimano XT system.

    Can anybody tell me why my rear pads would wear differently? The inner pad is almost worn out and the outer is in good shape. This is the first set of pads on the bike and they were centered to start with no rubbing.

  2. #2
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    if they are wearing unevenly, it is likely one pad is reaching the rotor before the other. A piston could be sticky or the caliper could have been a tad loose...

    Do the pads contact the rotor at the same time?

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    They appear to hit at the same time. I'd think for the brakes to work they would each have to see equal pressure of it would be pushing the rotor off to one side. It will probably become more apparent when I put a new set in.

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    Caution;  Merge;  Workers Ahead! Help - how do you reset pistons

    Newb question on Hydraulic brakes. How do you reset the pistons? Like I said above my pads have uneven wear and the inside piston extends much further than the outer. How do you get them back in? Do you have to bleed the system?

    I'm leaving for a week of camping and hopefully MTB tomorrow and most of my LBS are closed. If i can find one that is open I'll grab some new pads but I know they won't fit until the pistons are reset. I've seen reference to it all over this forum but not how.

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    OK, I figured it out. Just apply steady pressure and they eventually go. I got the new pads and they still appear centered with no drag.I'm still not sure what caused one pad to wear so much faster than the other. I'll see how this set does.

  6. #6
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    my xts do that also. They seem to stick on one side from time to time. I have to clean around the pistons with the pads off with a qtip and they work better. It's not really a big deal unless one side won't retract and the rotor just rubs all the time.

    Try this: take the wheel out, push the pads apart a little, and squeeze the lever. If both sides move about the same amount, don't worry about it, if not, take the pads out and clean the pistons.

  7. #7
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    Quote Originally Posted by bedwards1000 View Post
    They appear to hit at the same time. I'd think for the brakes to work they would each have to see equal pressure of it would be pushing the rotor off to one side. It will probably become more apparent when I put a new set in.
    Just because the pads look like they contact at the same time doesn't mean they are centered. Does the rotor flex at all when you squeeze the lever? If the caliper AND the pads are centered (note that a centered caliper does not equate to centered pads), there will be zero flex of the rotor when the lever is squeezed.
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    you either have sticky pistons or the caliper not centered which could easily be fixed by:

    1. loosen the caliper mounting bolt
    2. press on the lever allow it to bite the rotor
    3. while pressing on the lever tighten the bolts slowly making sure that the caliper body doesnt move during the process.

    hth

  9. #9
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    Quote Originally Posted by walangpakealam View Post
    you either have sticky pistons or the caliper not centered which could easily be fixed by:

    1. loosen the caliper mounting bolt
    2. press on the lever allow it to bite the rotor
    3. while pressing on the lever tighten the bolts slowly making sure that the caliper body doesnt move during the process.

    hth
    This is not the correct way to center a caliper. Sure its what Avid uses, and is the cause of the substantial majority of noise/power issues with Avid brakes in my opinion. It does not account for slow/sticky pistons.

    Centering the caliper needs to be done visually without pads in for best results, making sure that the rotor is centered in the brake track. Personally, I go so far as to use feeler gauges to ensure that they are centered. Then drop in the pads and centralize the pads manually.
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    Quote Originally Posted by OO7 View Post
    This is not the correct way to center a caliper. Sure its what Avid uses, and is the cause of the substantial majority of noise/power issues with Avid brakes in my opinion. It does not account for slow/sticky pistons.
    been using this method on my saint, non series and xt brakes for as long as i can remember. regardless of whether its wrong or correct, this method WORKS for me. never had avid brakes so i dont know anything about the noise/power issue. The op said hes using XT brakes.

    Quote Originally Posted by OO7 View Post
    Centering the caliper needs to be done visually without pads in for best results, making sure that the rotor is centered in the brake track. Personally, I go so far as to use feeler gauges to ensure that they are centered. Then drop in the pads and centralize the pads manually.
    how do you account for pistons that dont get pushed out far enough? and how do you exactly "centralize the pads manually" after aligning the caliper with the rotor without pads. im sorry im trying to understand your method, i have one that already works but i know there are more than 1 way to skin a cat.

  11. #11
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    Quote Originally Posted by walangpakealam View Post
    how do you account for pistons that dont get pushed out far enough? and how do you exactly "centralize the pads manually" after aligning the caliper with the rotor without pads. im sorry im trying to understand your method, i have one that already works but i know there are more than 1 way to skin a cat.
    I'm not sure what you mean by "accounting for pistons not getting pushed out far enough" . . . if they aren't getting pushed out far enough then you've got some non-functional brakes. At no point during setup am I pushing the pistons without pads installed.

    I run Hope's and these are their install vid's that show what I'm talking about. I've used this approach with other brakes as well.

    How To Video's - Hope How To Video's

    The problem with the "squeeze the lever and tighten the bolts" method is that you run the risk of having a sticky or slow piston during the "alignment" and then the caliper is positioned off center. While this results in the pads contacting the rotor at the same time, it may not be an equal application of force from both sides. Does it result in functional brakes? Yes, absolutely. However, if one pad is touching the rotor first or has to move farther to reach the rotor than the other, you're not getting the most power out of your brakes.
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  12. #12
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    Quote Originally Posted by walangpakealam View Post
    you either have sticky pistons or the caliper not centered which could easily be fixed by:

    1. loosen the caliper mounting bolt
    2. press on the lever allow it to bite the rotor
    3. while pressing on the lever tighten the bolts slowly making sure that the caliper body doesnt move during the process.

    hth
    This does not always work out so well.....it certainly can work...

    Sticky pistons, crude etc can confuse it...

    Best way

    Take the pads out set the caliper square and true to the rotor....you never have to adjust it unless it moves for some reason....(kinda like the IS mounts rather than post mounts...)

    Then install the pads....bingo they will work unless they are sticky or not moving properly.


    To Bedwards....

    Take the old pads out, and extend the pistons

    Wash the brakes with soapy water and rinse

    Push the pistons all the way in....then pull the lever if they move identically then you are good....if not extend the slow one by holding the faster one in with a pair of pliers....clean again...

    Repeat till they move identically....

    Re-align caliper with the rotor square and true....

    Install new pads....

    Check for absolutely free rotation....

    Then apply brakes and re-check for free rotation....if not then one piston is still sticky...

    When set get up to about 30 km/h and do three or four hard stops to start the bedding process....

    The ride like you stole it.

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    three

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    Are you talking about M775 or M785 XT Brakes? I have never had problems with the M785 sticking, but recall it being a slight issue on the M775. I find there isn't a lot you can do to permanently prevent that. You can try the suggestions others have already made. But if you are using a really true rotor, I believe some stick in a piston is not a big deal. It will still usually move away from the rotor enough to prevent constant rubbing. Are you using Shimano rotors with the alloy spider? I find that those rotors stay super straight, thus pretty much never rub. If you don't have those rotors, do you hear rubbing? If so, that could be your problem.

    If not, then I can think of another scenario that no one has mentioned. When I set up both my sets of M785 brakes, I followed the Shimano instructions for trimming the hose (found here http://www.shimano.com/publish/conte...20Trimming.pdf). But there is a problem with that that method that I believe exists on the M785, because there isn't much space for expansion of the fluid reservoir bladder. When you get to the point where you have cut and reconnected the brake hose, and it is time to push the pistons back into the caliper, you may find that you can push the piston all the way in but it will spring back out partway on its own as soon as you stop putting pressure on it. I believe that this is due to the small amount or air that was introduced to the system at the lever end during the hose trimming process. It has nowhere to go, so when you push the piston in, the air compresses in the fluid reservoir of the lever body, and when you let go, it uncompresses and pushes the piston out a little. To let that air out, just unscrew the torx bolt on the shiny cover you see on your lever. Do this while the lever is turned to keep the cover as level with the ground as possible. Then push the slave pistons in as far as they can go. Some air and some fluid will be pushed out of the cover on your lever, wipe it away. Once the pistons are all the way in, you can reseal the reservoir cover by tightening the torx bolt back up.

    This may not be your problem either but I know for me personally, I did not even have any free stroke on one brake until I did this "extra step." YMMV - has anyone else done the same process as me?

  15. #15
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    Hi All, thanks for all the good info. Good how-to jeffscott The brakes are M775. The new pair of pads did the trick in the short term. The brakes appear to be pretty clean an non-binding, both calipers extend the same distance. I got just about 1000 miles out of this set of pads so I can't complain.

    The outer pad deflects the rotor in slightly but the inner pad wears faster. It looks like if I center it with the brakes released it will rub but I'll see what can be done. I was mostly trying to get it functional for my trip. I'll leave it as-is for an event I have next weekend and then I'll tinker.

  16. #16
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    I don't think sticky pistons can directly cause premature pad wear as pronounced as described by the OP. If the pads were contacting something immovable, then sure, but the rotor is anything but. As the pistons move out and the pads engage the rotor, the rotor will bend sideways to accommodate for any difference in piston travel, thereby distributing the combined clamping power of the two pistons more or less equally to both pads. There will be a minute imbalance in forces between the pads as the bent rotor will push against one of the pads, but this force is almost negligible compared to the forces exerted by the pistons (the deflected rotor will also contact the pads at a slight angle, but this is true for both sides). In fact, most mechanical calipers work by deflecting the rotor into a fixed pad, a bit like a hydraulic caliper with one of the pistons completely stuck. And these mechanical brakes usually show fairly even pad wear.

    If, however, the sticky piston is causing one of the pads to rub, then it is a completely different story. Especially in muddy and gritty conditions pad rub can wreak some serious havoc, even with sintered pads.

    Also note that sometimes one pad just wears out faster than the other. Batch differences or manufacturing tolerances I guess. I've had this happen with one particular set of pads on set of brakes that worked fine prior and have since been used to wear through many sets of pads without any issues or adjustments.

    My suggestion is therefore to wait and see what happens with the new set of pads. Just keep the other, not-as-worn, pad from the first set around as a backup.

  17. #17
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    Same bike, same brakes, new - but maybe related question. I put the new pads on, centered the calipers and have put a few hundred miles on the bike. The back brakes are still not great. When I try to lock up the rear wheel the brakes give a low pitch squeal/vibration and don't lock up without excessive lever force. The rotors appear centered in the calipers and both calipers seem to extend and retract the same amount. I've tried intentionally justifying them to the inside and outside to see if anything changes. Under heavy braking all they do is howl at me.

    What else is there to try? Could it need to be bleed? The lever is still firm and can't be brought all the way to the bars.

  18. #18
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    Quote Originally Posted by bedwards1000 View Post
    Same bike, same brakes, new - but maybe related question. I put the new pads on, centered the calipers and have put a few hundred miles on the bike. The back brakes are still not great. When I try to lock up the rear wheel the brakes give a low pitch squeal/vibration and don't lock up without excessive lever force. The rotors appear centered in the calipers and both calipers seem to extend and retract the same amount. I've tried intentionally justifying them to the inside and outside to see if anything changes. Under heavy braking all they do is howl at me.

    What else is there to try? Could it need to be bleed? The lever is still firm and can't be brought all the way to the bars.
    Sounds like contaminated pads. A little oil or brake fluid on the pads will ruin them. Maybe that was the problem with the original uneven wear. Oil on one pad only. With XT's you should be able to lock it up easily. New pads, but don't put them in until you have cleaned the caliper and checked for leaks. I had a bleed port get loose on me and contaminated my pads. I had a Banjo leak do the same thing, and of course I did plenty of stupid things over the years that ruined my pads before I knew any better.

    Good luck!
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  19. #19
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    I have a new set of pads I can try to see if it fixes the problem. I've got no leaks. I have cleaned the rotors with alcohol and got nothing more than normal road grime off them so I don't think contamination is the problem but it is worth a try.

  20. #20
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    Quote Originally Posted by Prophet Julio View Post
    Sounds like contaminated pads. A little oil or brake fluid on the pads will ruin them. Maybe that was the problem with the original uneven wear. Oil on one pad only. With XT's you should be able to lock it up easily. New pads, but don't put them in until you have cleaned the caliper and checked for leaks. I had a bleed port get loose on me and contaminated my pads. I had a Banjo leak do the same thing, and of course I did plenty of stupid things over the years that ruined my pads before I knew any better.

    Good luck!
    This is definitely a possibility. I'd start by changing pads first . . . if that doesn't do it, time for a good bleed.
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  21. #21
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    Will a system with bubbles cause squeal? The lever seems pretty firm but maybe it could be better. I'm going to tinker this weekend but I won't be able to get my hands on a bleed kit.

  22. #22
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    Quote Originally Posted by bedwards1000 View Post
    Will a system with bubbles cause squeal? The lever seems pretty firm but maybe it could be better. I'm going to tinker this weekend but I won't be able to get my hands on a bleed kit.
    Yes, because the pad is not being pushed against the rotor with the same force as compared to a system without air.
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  23. #23
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    Boom, done, bleed kit and another spare set of pads are ordered. I'm sick of my honky brakes. I'll report back on the progress in a week or so when the kit comes in.

  24. #24
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    In my experience, this is what happens with Hope's when the system needs a bleed. The lever feels every so slightly difference, but the power diminishes quickly and the rear brake starts making lots of noise too.
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  25. #25
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    Going to be follwing this thread now.

    Back in May I ordered new M785's for my Tallboy build. The first few rides were great and the brakes awesome. The fronts have given me no issues whatsoever.

    The rears, however, seem to have developed a loss in power/squeal as described above. I tried lightly sanding pads and rotor on the original pads, which did not help. Fed up, I purchased a set of resin pads and again, lightly sanded the rotor. Boom, good as new, better even(I like the resin better). Now, after each ride, it seems that the symptoms return and I have to repeat the sanding process each time.

    I have kept an eye out for banjo and any other leaks....nothing. Not even any spots where it seems trail dust is collecting due to oil. My hoses have been shortened and levers feel pretty firm.

    two things: Are you saying that the smallest amount of air in the system could cause these issues...??

    And, Has anyone heard of any issues with oil seeping from the pistons on these...?? Sometimes when I take the pads out to sand them, I notice a light ring on the left pad....just barely enough to see where the piston contacts the pad. It isn't enough to even drip. Normal??
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