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  1. #1
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    Help...new to disc brakes.

    I have been riding and working on bikes for a while, but just picked up a used 2008 Stumpjumper Comp Hardtail , so I am a noob to some of the components. Two issues that I need some advice on:
    1. I have zero experience with disc brakes, and this has Avid Juicy 5s. There is some rubbing in the rear caliper. From reading other posts on here, I know that this isn't uncommon on these brakes. What's the best approach to resolving this?
    2. It has a fairly new XT bottom bracket that feels like it has an unusual amount of friction when spinning the cranks forwards or backwards, at least compared to my old one. Any advice on improving this or is the next step replacing the bottom bracket?
    Thanks for any help.

  2. #2
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    1. true the rotor and check to see that the pads are seated firmly.

    2. take it out and clean it, if it's clean there is a break-in period for the bearings. I wouldn't think so but check the bb shell width and installation instructions for the bb and crankset. Perhaps there is an additional plastic ring that results in too much pressure from the crank arm on the bearings. I'm assuming the crankset is a thru axle style. As long as it's not a creaking, popping hard rubbing gritty movement, it probably just needs some riding.
    No fuss with the MUSS

  3. #3
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    Thanks very much for the information. I'll carefully dig into the brakes like you suggested. It's a good chance to get to know my new bike before temperatures rise a bit.

    I can feel the friction in the bottom bracket, but definitely no off-axis movement, roughness, or noise. I'll try just exercising it a bit first.

    Thanks again!

  4. #4
    local trails rider
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    If the brake rubs consistently all around the circle, it could be a simple misalignment in the calliper. Usually that can be corrected by loosening the 2 bolts that hold the calliper to the adapter (that is fixed to the frame), squzzing and holding the brake lever, and retightening the bolts (while holding the lever).

    That doesn't quite always work, and then you may have to go for other ways to align the calliper with the rotor.

    Just having your quick release/axle seated a little different, or at a different tension can lead to a misalignment too, so actually checking your quick release might be the first thing to try with the brake.

    "it IS possible that you are faster or slower than anybody else who is having at least as much if not more or less fun"

  5. #5
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    Disc brake adjustments aren't difficult to do. But they require attention to detail and can be tedious. Avid brakes have these hemispherical washer stacks (CPS washers) that provide a lot of capability for adjustment, but also increase the tedium factor. The basic idea is that you want the rotor centered equally between the pads. There are a few techniques to get this result and you might need to try one or more to get it right.

    My Shimano bb's with external bearing cups have a lot of seal drag compared to the older bb types (square taper, octalink, etc). As long as the bb is smooth and quiet, I wouldn't worry.

  6. #6
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    Thanks very much for the detailed information. I'll leave the bb alone for now and work with the brakes. This site is a wealth of knowledge.

  7. #7
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    Quote Originally Posted by NateHawk View Post
    The basic idea is that you want the rotor centered equally between the pads.
    I thought you wanted the rotor closer to the piston side and not the fixed side, although that is the recommendation for the bb7s. Is this different for hydraulic? Please educate me.
    No fuss with the MUSS

  8. #8
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    Hydraulics don't have a fixed side, both move.

  9. #9
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    Then yes, rotor to the middle please.
    No fuss with the MUSS

  10. #10
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    Quote Originally Posted by canker View Post
    Hydraulics don't have a fixed side, both move.
    some cheap hydros have a fixed side...or at least had. I haven't seen any of those on the market for probably 8-10yrs, but they probably still exist. but yeah, any halfway respectable hydro has dual pistons.

  11. #11
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    If the wheel spins freely and you can just hear it rub once around for a quick zzzt then you may just not want to not worry about it. Yes, you can probably fix it by truing the rotor and/or adjusting the caliper but the fix probably won't last very long. As long as the wheel spins freely I don't consider it worth fixing.

    If the wheel gets noticeably slowed down then a fix is in order as described by others.

  12. #12
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    Thanks again for the help. A quick adjustment to the mounting bolts and she's rub free and I'm loving the brakes. Another question about disc brakes:
    Do wheels have to be retrued more frequently with disc brakes than rim brakes? When braking with disc brakes, the disc/hub want to stop and the rims/tires want to keep their momentum going. It seems that this would put significant torsional strain on the wheels and stress the spokes. Any thoughts from experience? Thanks!

  13. #13
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    In my experience they take less, I don't remember truing a wheel since I started running disc wheels. You should still keep eye on the spokes.

  14. #14
    Fat-tired Roadie
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    Re: Help...new to disc brakes.

    Quote Originally Posted by HTswede View Post
    Thanks again for the help. A quick adjustment to the mounting bolts and she's rub free and I'm loving the brakes. Another question about disc brakes:
    Do wheels have to be retrued more frequently with disc brakes than rim brakes? When braking with disc brakes, the disc/hub want to stop and the rims/tires want to keep their momentum going. It seems that this would put significant torsional strain on the wheels and stress the spokes. Any thoughts from experience? Thanks!
    They do distribute more stress to the spokes. That's why we haven't seen any half-radial wheels for mountain bikes in a while.

    Using a traditional semi-tangent pattern, which is almost all wheels, the load paths are pretty reasonable. I'm not sure how much tension spokes typically have and haven't worked out how much additional tension it would take to stop a bike, but figuring that out (well, I could just look up the spoke tension part) would be my next step.

    I think I spend less effort maintaining my MTB wheels than my road wheels. Road tires don't provide a lot of protection.

    I haven't had a rim brake MTB in many years. I remember truing its wheels a lot but it was a cheaper bike and I wasn't a brilliant mechanic at the time. Of course, I'm a brilliant mechanic now. I'm also very attractive and never break taps.
    "Don't buy upgrades; ride up grades." -Eddy Merckx

  15. #15
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    lol. yeah, I don't do nearly as much wheel maintenance with disc brakes. very subtle wobbles don't matter when your braking surface is a disc. You still want to keep an eye on them because if you develop a more significant wobble, you still want to address it before you start breaking spokes.

    My wife's wheels have been out of service for about a month now because a couple spoke nipples on the back wheel disintegrated over the winter (probably due to improper maintenance in the past - we bought them used, and have recently learned quite a bit about how DT Swiss Tricon wheels are much different than other wheelsets) and one of the flat bladed spokes on the front wheel has twisted. I'm hoping they're ready to go this week.

    I have trued my Mavic CrossTrail wheelset once since I bought them about 9 years ago. They have been so solid that they haven't needed more.

  16. #16
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    Thanks for the thoughts. It is tough to truly compare the effects of the two brake types on the spokes with so many other variables. I am glad to hear that there doesn't seem to be any appreciable ill effect on the spokes. Either way, I certainly need to work on my wheel trying skills.

  17. #17
    Fat-tired Roadie
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    On a mountain bike, the limiting factor on wheel torque tends to be that the tire breaks free. So a quick qualitative thought is that if my wheels survive the torque it takes me to break the tire free by pedaling, which is pretty easy, they'll be okay under braking too.
    "Don't buy upgrades; ride up grades." -Eddy Merckx

  18. #18
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    In the early days of disc brakes before frame design caught up, rather then spoke problems, chainstays seemed to be the weak point of the equation. Wheels always seemd to do fine, but concentrating all that braking force on an inch of frame led to a good few failures.
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  19. #19
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    Interesting. I'm certainly less concerned about my wheels after the early frame failure information. Was is the chain stays themselves or the caliper mounts on the chain stays. Thanks again for the history!

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