XT 8000 brakes, canít get rid of rotor rubbing- Mtbr.com
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  1. #1
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    XT 8000 brakes, canít get rid of rotor rubbing

    Iíve has a lot of Shimano hydro brakesótwo sets of 785, 985, RS785 (road), two RS805 (road), and now 8000. Never had any issues with any of them.

    I build all my bikes so I did the caliper centering, bleeding, etc on all of these but I just canít get rid of rubbing on the 8000ís. Iíve bled the brakes, cleaned the pistons with alcohol so they cycle smoothly and donít stick, new pads, new rotors, and a dozen cycles or pushing the pistons in, loosening caliper bolts, grabbing brake lever, and tightening caliper bolts, the method I gave always used.

    Are these brakes hard to set up? Is there some setup step Iím missing? Iíve gotten it to the point it only rubs after hard braking and everything expands a little but never had it on 6 other sets so why these?

  2. #2
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    Quote Originally Posted by Alias530 View Post
    ...loosening caliper bolts, grabbing brake lever, and tightening caliper bolts, the method I gave always used.
    There is an inherent flaw in that technique. Even though I use it most of the time, the problem is when you get little indentations in your brake mounts and caliper and they become "keyed". So after a while, whenever you do this technique, the caliper will always move to the same place. Also, look at the caliper real closely when tightening the bolts, you'll probably notice it twists a little. At times, I have had to push the caliper with a 3rd hand to keep it aligned while squeezing the lever and tightening.
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  3. #3
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    I prefer to tighten the caliper by looking at the gap between the pads and rotor, if you don't have a warped rotor nor a sticky piston, you can get your rotor dead center between your pads, it never failed me. The method of squeeze your lever and tighten your caliper is always a hit or miss.

  4. #4
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    Quote Originally Posted by Jayem View Post
    There is an inherent flaw in that technique. Even though I use it most of the time, the problem is when you get little indentations in your brake mounts and caliper and they become "keyed". So after a while, whenever you do this technique, the caliper will always move to the same place. Also, look at the caliper real closely when tightening the bolts, you'll probably notice it twists a little. At times, I have had to push the caliper with a 3rd hand to keep it aligned while squeezing the lever and tightening.
    I assumed the twist was because the hose was pulling it to one side and the twist was just centering it. It's always worked in the past but I guess I'll try centering it with my eyes.

  5. #5
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    Quote Originally Posted by Alias530 View Post
    ...loosening caliper bolts, grabbing brake lever, and tightening caliper bolts, the method I gave always used.
    Normally that works for me too, but for some reason I occasionally have to resort to jamming the thickest shims I can in on both sides, squeezing the lever and then tightening the bolts.

    I have a set like this and think I use 0.018 and 0.019"

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  6. #6
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    Quote Originally Posted by Aglo View Post
    I prefer to tighten the caliper by looking at the gap between the pads and rotor, if you don't have a warped rotor nor a sticky piston, you can get your rotor dead center between your pads, it never failed me. The method of squeeze your lever and tighten your caliper is always a hit or miss.
    ^^^ this.
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  7. #7
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    Quote Originally Posted by J_Westy View Post
    Normally that works for me too, but for some reason I occasionally have to resort to jamming the thickest shims I can in on both sides, squeezing the lever and then tightening the bolts.

    I have a set like this and think I use 0.018 and 0.019"

    Click image for larger version. 

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    I imagine a business card or similar would work too. I've thought about trying this but wouldn't the pads just auto adjust inwards to the same position they'd be if you didn't use shims when tightening once you start using them?

  8. #8
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    Quote Originally Posted by Aglo View Post
    I prefer to tighten the caliper by looking at the gap between the pads and rotor, if you don't have a warped rotor nor a sticky piston, you can get your rotor dead center between your pads, it never failed me. The method of squeeze your lever and tighten your caliper is always a hit or miss.
    This, and to help overcome the "keying" that Jayem mentioned, do two things.

    (1) Once the caliper is centered over the rotor, iteratively tighten each bolt, a little at a time, checking for rub as you go, and making any small adjustments. The easiest way to do this is with the bike upside down, with a white or light-coloured background underneath, so that there is high contrast and one can easily see the pad gap.

    Using this technique I can get "keyed" 9 year old Formula brakes to be rub free...the same Formula brakes that have very little pad roll-back and are prone to rub.

    (2) After this, if one ends up with rubbing due to the the pistons being slightly unbalanced, then go back and adjust the alignment to account for this.

  9. #9
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    ^^^
    What Aglo and PD said.
    I find it easiest with my caliper in the shade, and sighting through the rotor/pad gap at a sunny spot on the ground.

  10. #10
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    Flash light helps (shine light through opposite side of caliper) Helps to see the gap on either side of the rotor.

    Watch your fingers!
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  11. #11
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    I use the squeezing the brake while tightening the mount bolts trick to get me close. Then I slightly loosen the bolts and push the caliper over until the pads no longer rub.

  12. #12
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    Quote Originally Posted by Jayem View Post
    There is an inherent flaw in that technique. Even though I use it most of the time, the problem is when you get little indentations in your brake mounts and caliper and they become "keyed". So after a while, whenever you do this technique, the caliper will always move to the same place. Also, look at the caliper real closely when tightening the bolts, you'll probably notice it twists a little. At times, I have had to push the caliper with a 3rd hand to keep it aligned while squeezing the lever and tightening.
    9 times out of 10, this is the problem I see and, I see a ton. Not just Shimano, but any caliper can have this issue. I file down the tabs just enough to get rid of the indents in the coating. Problem solved every time.

  13. #13
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    Quote Originally Posted by mlx john View Post
    Flash light helps (shine light through opposite side of caliper) Helps to see the gap on either side of the rotor.

    Watch your fingers!
    This is the way I do it also but once tightened I make sure the rotor doesn't deflect to either side with the lever pulled, that can definitely happen if one of the pistons is a little lazy. If that's the case I just tighten the rotor so the the pad of the lazier piston is closer to the rotor than the other side until I can do a full brake service.

    Either way, the important part is making sure the rotor doesn't deflect to either side with the levers pulled imho.
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