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Thread: xt m775 issues

  1. #1
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    xt m775 issues

    Hi! I just installed a new set of m775 xt brakes on my rig and have had nothing but headaches with them and was hoping for some insight. I seem to be having two separate issues with my rear setup.

    Issue 1: upon braking there is very little power (to be expected as they are brand new) but as apply more pressure the brakes start to grind and squeal culminating on a very deep vibration as the brakes finally grab. I've already bled the brakes (had to switch the lines as they came pre-assembled backwards), I've checked all of the rotor bolts, and re-aligned the caliper a million times. Any ideas what else to try/redo/look into?

    Issue two: on the lever it seems that the actuation piston is somewhat sloppy compared to the other lever. The brass bushing on the bottom in the guide channel is able to click to the very end of the channel (god I hope that makes sense). Is this a legit situation or something menacing? To answer the obvious question... No, the brakes haven't been crashed on.

    Thanks the insight.

  2. #2
    DGB
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    Another couple of things to check for issue #1 (and you may have done this already, so don't take offence).
    From reading your previous posts, I see you are not a newb so I'll presume you know how to bed-in pads.

    What I've found is that anytime I get squealing from my M775s is when I've got some sort of contaminant on either the pads and/or the rotors.
    You may have inadvertently gotten some mineral oil on either the pads and/or the rotors when you were swapping over the brake lines or bleeding. I'd clean the rotors thoroughly with some alcohol and flame the pads over a gas burner until they get good and hot to burn off any contaminants, which you will see as smoke.
    Repeat the bed-in process and you should be good to go.
    Failing that, check that the rotors are installed with the correct rotation.

    As for issue #2, I know what you mean. (I'm currently looking at a broken MC in my hand). If you push the lever away from the bar this brass bushing also moves further to the front of the "channel". This is normal and happens in all of the M775 levers I've seen.

    This brass bushing is adjusted by means of the free-stroke adjustment screw. If you turn the free-stroke adjustment screw out (anti-clockwise), the brass bushing moves further to the front of the "channel" that you mention and vice-versa when you go clockwise.

    I hope this helps.

  3. #3
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    ...twanged rotor...

    Say Folks, does anyone have a trick way to straighten slightly bent disc brake rotor? I have my way of doing this (rubber mallet/visible correction after marking) but it is time consuming. I do this process right on the bike using the caliper as a "truing stand". any better idea"s...big and tall

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    DGB,

    Thanks for the ideas, I did bed the brakes in properly so that is at least one thing off the check list. I verified rotor orientation this morning all is well there. Also, while bleeding I removed the pads and installed the supplied bleeding spacer. I am quite certain I did not get any mineral oil on the pads during these processes. BUT, this does not mean that during the shipping/factory assembly and bleeding process something didn't get splashed on the pads. I will go ahead and torch them tonight when I get home from the office and see if that helps correct the situation.

    (issue #2) good to hear its somewhat normal, I was just concerned as one lever did it and the other did not... maybe its just a matter of time before the other one joins the club.

  5. #5
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    Quote Originally Posted by big and tall
    Say Folks, does anyone have a trick way to straighten slightly bent disc brake rotor? I have my way of doing this (rubber mallet/visible correction after marking) but it is time consuming. I do this process right on the bike using the caliper as a "truing stand". any better idea"s...big and tall
    Truing rotors are better done with a truing fork OR a crescent wrench dialed into the thickness of the brake rotor. find the area that's out of true and bend accordingly. I would steer away from using the rubber mallet method as there is no guarantee of accuracy and you may be able to damage the rotor.

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    ...truing rotors 2.0...

    Thanks for the input markjk4, the cresent wrench method does seem to be a better Idea. I"m going to true the rotor up on my Hanebrink Extreme Terrain that way asap. Should quiet my Avid Juicy 3.5 "s down nicely...big and tall

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    Quote Originally Posted by markj2k4
    DGB,

    Thanks for the ideas, I did bed the brakes in properly so that is at least one thing off the check list. I verified rotor orientation this morning all is well there. Also, while bleeding I removed the pads and installed the supplied bleeding spacer. I am quite certain I did not get any mineral oil on the pads during these processes. BUT, this does not mean that during the shipping/factory assembly and bleeding process something didn't get splashed on the pads. I will go ahead and torch them tonight when I get home from the office and see if that helps correct the situation.

    (issue #2) good to hear its somewhat normal, I was just concerned as one lever did it and the other did not... maybe its just a matter of time before the other one joins the club.

    Try greasing the rotor where in contacts the hub, or splines if it is centerlock.

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    Quote Originally Posted by jeffscott
    Try greasing the rotor where in contacts the hub, or splines if it is centerlock.
    Im going to degrease the whole rear end (rotor, contact points, caliper etc.) and torch the pads, I would love it if it was just contaminated parts.

  9. #9
    DGB
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    Quote Originally Posted by markj2k4
    Also, while bleeding I removed the pads and installed the supplied bleeding spacer.

    (issue #2) good to hear its somewhat normal, I was just concerned as one lever did it and the other did not... maybe its just a matter of time before the other one joins the club.
    You might have got some oil on the rotors, maybe. So give them a quick clean, just to be sure.
    Adjusting the free-stroke screw should sort even out the lever differences.

  10. #10
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    Quote Originally Posted by markj2k4
    Im going to degrease the whole rear end (rotor, contact points, caliper etc.) and torch the pads, I would love it if it was just contaminated parts.

    Thats fine but three things

    Apply grease on the contact points to help damp vibrations...

    And I find heating the pads in a fry pan on medium heat works better than a torch.

    If you are going that far you should very lightly sand the pads after heating,

    sand the rotor once the wheel is back on the bike, to break and glaze.

    Just spin the wheel, with a piece of sand paper between your fingers squeezing the rotor.

  11. #11
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    yea... absolutely no dice with any attempt at stifling the resonance. Here's what has taken place:

    torching pads
    sanding and cleaning rotors
    lightly greasing the hub contact point on rotor
    adjustment of caliper alignment (several times)
    greasing of the dropouts
    tightening of the dropouts
    alignment of the dropouts

    nothing.

    I am wondering if it will eventually just fade away and I am just experiencing the brakes hitting a perfect frequency to resonate the frame. I can feel the vibrations substantially in the seat and handle bars.

    for reference frame is a voodoo d-jab (titanium with sliding dropouts) setup as a single speed with king hubs.

  12. #12
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    Quote Originally Posted by markj2k4
    yea... absolutely no dice with any attempt at stifling the resonance. Here's what has taken place:

    torching pads
    sanding and cleaning rotors
    lightly greasing the hub contact point on rotor
    adjustment of caliper alignment (several times)
    greasing of the dropouts
    tightening of the dropouts
    alignment of the dropouts

    nothing.

    I am wondering if it will eventually just fade away and I am just experiencing the brakes hitting a perfect frequency to resonate the frame. I can feel the vibrations substantially in the seat and handle bars.

    for reference frame is a voodoo d-jab (titanium with sliding dropouts) setup as a single speed with king hubs.
    I had the same issue with brand new XT M775's as well. Tried everything you did.
    I sold them on ebay...

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    Yea, I am hoping to get it sorted, the brakes are pretty nice otherwise. If wearing them in does not work, I will try new pads (oe or non-oe) and see if that helps. If not I may have to pass them on as well and try something else.

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    crap, did you order these from ribble? I just ordered some from there, I hope they dont have the same issue.

    I <3 the m775 brakes that came with my anthem......

  15. #15
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    Ordered from merlincycles... I am sure you should be just fine. I doubt its anything really major anyways, there's so many other factors that can cause problems besides the obvious problems with the brakes... e.g., loose hub, unfaced frame, contaminated parts etc. If it's any consolation (for me) braking power has exponentially increased but most of the irritatingly loud vibration is still present. It's more embarrassing than problematic anyways...

  16. #16
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    are you using the resin or sintered pads?
    Ive had alot of issues with the sintered

    also make sure the pistons are comming out evenly, if not you need to re center the pistons

  17. #17
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    Quote Originally Posted by dan0
    are you using the resin or sintered pads?
    Ive had alot of issues with the sintered
    They came equipped with sintered pads... I may switch to organic pads, still up in the air. I do ride the entire rain season here (San Francisco) and prefer sintered's abilities to withstand wet riding, but much rather have the peace and quiet of organic if it came down to it.

  18. #18
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    I found that the sintered pads that came with the m775 were unbelievably loud and jittery, but stopped okay. I switched to Fibrax metallic pads and they stop just as well, but without the noise and vibration. I haven't used organic pads for a while, so I can't say much about them.

  19. #19
    DGB
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    Quote Originally Posted by markj2k4
    They came equipped with sintered pads... I may switch to organic pads, still up in the air. I do ride the entire rain season here (San Francisco) and prefer sintered's abilities to withstand wet riding, but much rather have the peace and quiet of organic if it came down to it.
    If you're riding in the wet, IMO, you're better off to stick with the metal pads. The resin ones don't last at all in wet n' gritty conditions and I've found that their braking performance is not up to the level of the metal pads in those conditions.

    I'm wondering is there an issue with the sliding dropouts on your frame causing the resonance - ensure they're tightened to the correct torque and I'd use some threadlock to prevent them from loosening. This might help with the noise.
    Is the noise as bad from the front brake as the rear?

  20. #20
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    Quote Originally Posted by DGB
    If you're riding in the wet, IMO, you're better off to stick with the metal pads. The resin ones don't last at all in wet n' gritty conditions and I've found that their braking performance is not up to the level of the metal pads in those conditions.

    I'm wondering is there an issue with the sliding dropouts on your frame causing the resonance - ensure they're tightened to the correct torque and I'd use some threadlock to prevent them from loosening. This might help with the noise.
    Is the noise as bad from the front brake as the rear?
    Yea, I totally know about the wet stuff and resin pads.

    in referencing the front brake it's like night and day. While it isn't silent, it is as quiet as it should be, hardly making more than a slight squeeky chant under hard braking. The rear sounds like a tuba in comparison. I think I might pull the rear end apart again, clean the drop out channels then apply a liberal amount of fiber-grip to both dropout and re-install. Metal on metal contact can sometimes do naughty things.

  21. #21
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    Quote Originally Posted by markj2k4
    Yea, I totally know about the wet stuff and resin pads.

    in referencing the front brake it's like night and day. While it isn't silent, it is as quiet as it should be, hardly making more than a slight squeeky chant under hard braking. The rear sounds like a tuba in comparison. I think I might pull the rear end apart again, clean the drop out channels then apply a liberal amount of fiber-grip to both dropout and re-install. Metal on metal contact can sometimes do naughty things.

    try swapping the pads from front to rear, that will eliminate one possibility

    Im now to the point of trying a different rotor, Ive done everything else

  22. #22
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    Quote Originally Posted by dan0
    try swapping the pads from front to rear, that will eliminate one possibility

    Im now to the point of trying a different rotor, Ive done everything else

    Well sir, there was a factor that I never really considered... two entirely different pads (fronts were organic and quiet and the rears were sintered). now I have a some what squeeky front end (not nearly as bad as the resonance I got from the rear) and a silent rear. I do have a larger rotor on the front so I will rebed in the front brakes and roll it with the sintered for a few rides and see if it quiets down. If not I would be willing to take suggestions as to quieter metallic/semi-metallic pads for the winter. I do prefer low noise as sometimes adventures take me into areas where I rather not stir up wildlife or areas where boundaries are questionable.

  23. #23
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    I hear ya
    I also tried goodridge sintered, loud as well. maybe a different brand of rotor might work?
    I have an avid rotor on my other bike, Ill swap it and see, more tomorrow

  24. #24
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    Shimano Sintered pads made a hell of a racket, Clark's organics solved all of my noise issues, though I used the noise as an excuse for some Alligator Serration rotors and love them.

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    ...brake pads...

    I"ve had good results using the pads that came with my Avid Juicy 3.5"s. Does anyone know what the part number is for these units? I"ve never had to take them out of the calipers (new bike) and i want to order a spare set for future use...big and tall

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