Need Help with Mech Disc Brakes- Mtbr.com
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  1. #1
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    Need Help with Mech Disc Brakes

    I'm probably going to post in the Brake forum too, but since it's on a singlespeed I thought I'd try here first.

    I have a relatively new Civilian Luddite (rigid SS 29er) with Avid BB7 mechanical disc brakes. After approximately 4 trail rides, the next time I took it out, the rear brake was giving me trouble. Engaging the lever was not smooth. Best description would be sticky or not fluid.

    I've tried adjusting everything I know to do with the pad alignment, the position of the brake arm / cable, and the barrel adjuster, but no luck. The brake arm seems to work fine when disconnected from cable.

    And one more thing, when I get it adjusted as best I can, I can't lock the rear wheel. I can grab the front lever and can't physically push the bike and make the wheel turn, but when I do the same on the rear, no matter how hard I pull the lever, I can still push the bike and make the rear wheel and rotor turn through the pads.

    Any ideas? I'm clueless on my first bike with disc brakes.

  2. #2
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    Check where it enter/exits the cable housing. You might want to lube there too.

  3. #3
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    It's a cable issue.

  4. #4
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    Cables are basically brand new. So possibly just a lube issue? What type of lube would you guys suggest?

    Any ideas on why it may have malfunctioned? Does water create that kind of problem? Someone did accidentally leave the bike outside in a monsoon before this happened.....

  5. #5
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    Yup, if cables rust inside the housing it can create a world of issues.

    I remove the cable from the housing and run WD40 into the housing until it runs out the other end. Hang vertically for 5 minutes to let the excess run out. Wipe the cable itself with a WD40-soaked rag and re-install.

    Should hopefully solve the issue, unless the cable or housing is damaged or kinked in any way...

    Good luck!

  6. #6
    CB2
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    My guess is the brake cable has a kink in it.

    As far as not stopping the bike, adjust the static pad so it is a click away from just rubbing and the moving pad to engage how ever far out you like your brakes to grab.

  7. #7
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    Good advice guys - I'll check for rust and kinks and report back. Too bad I'm at the office....

  8. #8
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    yeah, definitely sounds like a cable issue. If moisture gets in there, they'll corrode and bind up. I find that a few drops of light chain lube - not waxy stuff - will help smooth things out. I typically use prolink gold. If there's a kink in the housing, you might need to replace it.

  9. #9
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    - Check for burrs at the ends of your cable housing.
    - If you're not using compressionless brake cable housing then I highly recommend you switch to it. It makes a huge difference, especially on the rear brake. To save money ou can buy the Nashbar compressionless brake cables which are just rebranded Jagwire with a cheaper inner cable.
    - Make sure the pads and disc aren't contaminated with oil.
    - Set cable tension with the caliper arm all the way extended, and then bring the pads in.

  10. #10
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    This is what the cable looks like (stock photo).
    Attached Thumbnails Attached Thumbnails Need Help with Mech Disc Brakes-luddite-zoom8.jpg  


  11. #11
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    Quote Originally Posted by ply5013 View Post
    This is what the cable looks like (stock photo).
    You can't tell from the picture, but it's most likely not compressionless.

  12. #12
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    Is there any chance you got oil on the disk? From lubing the chain maybe?
    I had the rustproofing stuff drip out of the frame onto the rear disk and it killed the rear brakes. Brake didn't do anything.
    Cleaned the disk with brake cleaner and steel wool, then brake cleaner again, soaked the pads in brake cleaner and sandpapered them. Almost back to normal but still not as good as they should be. Since it's a rear brake, I can get away with it.

    When you disconnect the cable from the brake, does pulling the lever or the cable feel easy and smooth? I'd pull the cable and housing out, check all the ends that they are flat and look good, the inner housing is good and not pinched and reassemble. A very small amount of grease might help.
    WD-40 should never be used on a bike.

  13. #13
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    Quote Originally Posted by Slash5 View Post
    Is there any chance you got oil on the disk? From lubing the chain maybe?
    I had the rustproofing stuff drip out of the frame onto the rear disk and it killed the rear brakes. Brake didn't do anything.
    Cleaned the disk with brake cleaner and steel wool, then brake cleaner again, soaked the pads in brake cleaner and sandpapered them. Almost back to normal but still not as good as they should be. Since it's a rear brake, I can get away with it.

    When you disconnect the cable from the brake, does pulling the lever or the cable feel easy and smooth? I'd pull the cable and housing out, check all the ends that they are flat and look good, the inner housing is good and not pinched and reassemble. A very small amount of grease might help.
    WD-40 should never be used on a bike.
    There's a chance some cleaner on the pads, but I still get the rough pull when the cable is loose too - just not as much.

  14. #14
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    Must be a defective cable or caliper, I have the same bike and can lock the front or back with one finger.

  15. #15
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    just get hydro disc brakes.

  16. #16
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    Quote Originally Posted by jan_kaspar View Post
    just get hydro disc brakes.
    The BB7 is an excellent disc brake.

  17. #17
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    Quote Originally Posted by jan_kaspar View Post
    just get hydro disc brakes.
    And send me those worthless mechanicals.

  18. #18
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    Quote Originally Posted by Slash5 View Post
    WD-40 should never be used on a bike.
    Let's agree to disagree.

    WD-40 BIKE | A comprehensive line of bicycle care products developed for cyclists and mechanics

  19. #19
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    Quote Originally Posted by divernick View Post
    I remove the cable from the housing and run WD40 into the housing until it runs out the other end...
    what? wd-40? shame! wd-40 did release a bike-specific line of lubes and the first I heard of those was about a month ago. when most people mention wd-40, they are talking about Water Displacement Formula 40, aka Bicycle Killing Substance 40. in general, it has very few uses on a bicycle and lubing cables is not one of them.

    wd-40 might be helpful to clean out any junk that might be in the housing and to clean corrosion off the metal wire of the cable, but it is not a good long-term solution for lubrication. it evaporates quickly and leaves the cable dry and open to corrosion. this is why you don't use wd-40 on chains.

    the best lube for cables is Shimano Special Grease, which might be hard to come by. I usually just use Triflow. nothing will substitute a straight, clean cable, but I like my cables to be in a bath of Triflow at all times.

  20. #20
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    Personally I'm a fan of using teflon coated cables without lube. I've found lube just attracts dirt and makes the problem worse.

  21. #21
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    I' a fan of using no cables: singlespeed with hydraulic brakes are my cup of tea....

  22. #22
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    Update: Haven't had time to work on this (rode a few times with it as is...priorities huh?). My small town has a LBS that doesn't get much business, so I did us both a favor and dropped her off there. They suspect the same problems you guys mentioned here. Will post results.

  23. #23
    HOV
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    I'm sure you already checked this, but the cable end was still fully seated in the lever, right? Cable removal slots staggered?

    Cable could have stretched over the frist few rides, then been bumped out of the intersection of lever and cable housing. I've had that happen a few times.

  24. #24
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    Alright guys, as most of you suspected,there verdict was a kinked cable. Not sure how it happened, but all is well now. Thanks for all the advice.

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