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  1. #1
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    Changing rear tire on MTB--brakes questions

    I'm still quite new to fixing flats on my MTB--have only done it a couple times. I keep running into this issue: I find it challenging, when putting the rear wheel back on the MTB, to not have any rubbing coming from the disc brake.
    The last time, I got so frustrated I took it to my LBS and the guy just sort of magically did it in about 2 seconds in front of me
    So today, I just fixed a rear a flat, and I'm following the steps the LBS mechanic showed me(putting weight on the seat to make sure the wheel is in the dropouts correctly for example), and I still find it hit and miss: I have to unlatch and relatch the quick release over and over until I get it to where there isn't a slight rubbing between the pads and the disc.
    Finally, I've got it now where it doesn't seem to rub if the bike is perfectly vertical, but if I lean it a hair to the side and rotate the rear wheel I notice a little rubbing (this is when I have it up on one of those little stands that holds it up by the seatstay and chainstay). Not during the entire revolution of the wheel, just intermittently as it rotates. My LBS just performed a tuneup on this bike a few days ago, and I'm confident it wasn't rubbing prior to my fixing this flat, so I assume the brakes are otherwise OK.

    Is there any special trick to getting that back wheel on and not having to struggle with the rear brake like this?

    Also, I understand it's bad to flip a bike with hydraulic brakes upside down. Well, I did that briefly today during my rather clumsy tire changing escapade. Aside from the slight rubbing I describe above, the brakes certainly seem to be working fine, so is it safe to assume I didn't do any damage flipping it over?
    2013 Specialized Allez Comp

  2. #2
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    As the shop mechanic showed you, one key is to have the wheel find it's home by gravity. Stand the bike up vertical on a flat area (no need to push on the saddle) and juggler the frame slightly to help the wheel settle past any places where it might bind. Also do this in high gear, which not only makes it easier to remove and replace the wheel past the RD, but also lowers the chain tension so it doesn't try to pull the right side forward

    Once this is done few times to confirm that it's the same each time, then adjust the brake around this position, and you should hit it spot on each time thereafter. Note that if there's any play in the hub'[s bearings, leaning the bike can shift the wheel enough for a bit of rub. If it's only occasional you can live with it, or try to reduce the hub play. Some bikes with rear suspension are also prone to this rub when leaning due to flex and movement in the swingarms.
    FB
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    An ounce of diagnosis is worth a pound of cure.

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  3. #3
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    Quote Originally Posted by FBinNY View Post

    Once this is done few times to confirm that it's the same each time, then adjust the brake around this position, and you should hit it spot on each time thereafter. Note that if there's any play in the hub'[s bearings, leaning the bike can shift the wheel enough for a bit of rub. If it's only occasional you can live with it, or try to reduce the hub play. Some bikes with rear suspension are also prone to this rub when leaning due to flex and movement in the swingarms.
    Thanks for the advice! I'm not quite clear though on what you mean by "adjust the brake around this position", or what follows---how do I adjust the brake and the hub play? This is a hardtail, BTW.
    2013 Specialized Allez Comp

  4. #4
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    You don't need to adjust the hubs unless there is play and the rim can move side to side freely more than 1-2mm. (not talking flex, but free paly). If the hubs need adjusting, the method depends on the hubs, but you can se=arch for tutorials on adjusting hub bearings.

    Likewise with the brake, The adjustment method is specific to the brake, with mechanical brakes (usually) allowing easy adjustment of each shoe independently. Hydraulics require centering the caliper itself. Again, the method is specific to the brake, but there are plenty of tutorials.


    In any case, the key is being able to repeatedly and consistently get the wheel to settle in the same place, and I'd practice that until I had it dialed in before making any adjustments.
    FB
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    An ounce of diagnosis is worth a pound of cure.

    “Never argue with an idiot. He will only bring you down to his level and beat you with experience.”, George Carlin

    “One accurate measurement is worth a thousand expert opinions” - Adm Grace Murray Hopper - USN

    WARNING, I'm from New York. Thin skinned people should maintain safe distance.

  5. #5
    Senior Member zukahn1's Avatar
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    With moderate skill one should be able to swap out a flat rear tube on bike in a matter of minutes it should not be a major choire.

  6. #6
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    Quote Originally Posted by FBinNY View Post
    You don't need to adjust the hubs unless there is play and the rim can move side to side freely more than 1-2mm. (not talking flex, but free paly). If the hubs need adjusting, the method depends on the hubs, but you can se=arch for tutorials on adjusting hub bearings.

    Likewise with the brake, The adjustment method is specific to the brake, with mechanical brakes (usually) allowing easy adjustment of each shoe independently. Hydraulics require centering the caliper itself. Again, the method is specific to the brake, but there are plenty of tutorials.


    In any case, the key is being able to repeatedly and consistently get the wheel to settle in the same place, and I'd practice that until I had it dialed in before making any adjustments.
    Thanks again for helpful reply. The more I do it I'm sure I'll get more dialed in! If nothing else, I'm getting REALLY fast at taking the wheel on/off
    2013 Specialized Allez Comp

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