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  1. #1
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    Strange Shimano disk brakes problems

    I have a mountain bike with Shimano XTR hydraulic brakes.

    I developed some sort of problem with my front brake whereby it became very noisy and very ineffective.

    I have tried several things including:-

    lightly sanding the pads
    cleaning the rotors with brake cleaning alchohol
    fitting new pads
    bleeding the system
    ..and even a new Shimano rotor on the advice of my local shop.

    There is plenty of pressure and no sign of any leaks.

    After replacing the rotor, things did seem better at first - but then quickly deteriorated back to being very poor and very noisy.

    I then tried swapping the pads from front to rear. Again, this seemed better at first, but again, things soon went back to the original problem, except now I have bad brakes on the front and the rear.

    Strangely, I have noticed that when the brakes are wet, they a very good and perform as I would expect them to!

    I'm desperate, can someone please tell me where I am going wrong.

    Thanks

    John

  2. #2
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    Sounds like a leak to me. Check the piston seals.

  3. #3
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    But the levers are both firm, I'm not losing any pressure and there are no obvious signs of leaks.

    Also the problem transferred to the back brake after I swapped pads between front & rear.

  4. #4
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    When you swapped pads front to rear, you said the rear started having problems, then the front quickly deteriorated as well, right?

    If so, then something is causing the front pads to be contaminated. It's gotta be some sort of leak. Might be a small one. Small enough to not be easily detected. It doesn't take much to ruin pads.

  5. #5
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    In my guest that oil leak!!!!!! it the same problem that i saw. my ride gang use XTR trail in 3 bikes and saw this problem in all bike i ve lucky cos my mojo is only front brake, but another seem to be bad luck cos they have problem all (rear+front) you need to replace hydrolic cable
    (it must be free!!) why shimano fail to QC they top line product
    check my photo


  6. #6
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    and i grill my oily pad to drain many oil out and it work

  7. #7
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    It's also possible that oil from the fork is getting onto the rotor and contaminating the pads.

    As hinted at above, some have had luck restoring contaminated pads by baking or boiling them.
    I can barely get my mouth around it.

  8. #8
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    I've just looked again really closely for any signs of leaks around the caliper or from the forks - everything looks really dry. No signs of oil anywhere.

    If the brake fluid was leaking, there would be some sort of pressure loss and the lever would start to feel spongy, right?

    Also, as I said earlier, when the brakes are wet, they still work very well. If the pads were getting contaminated, wouldn't they be degraded in the wet as well as when they are dry?

  9. #9
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    If it's not a leak then you may possibly riding through some contaminated liquid (such as water) that leaves a residue on your brakes after it dries. But the fact that it is only the front brake that has issues leads to a leak somewhere.
    fee-fy-fo-fum...

  10. #10
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    Quote Originally Posted by johna7770
    I've just looked again really closely for any signs of leaks around the caliper or from the forks - everything looks really dry. No signs of oil anywhere.

    If the brake fluid was leaking, there would be some sort of pressure loss and the lever would start to feel spongy, right?

    Also, as I said earlier, when the brakes are wet, they still work very well. If the pads were getting contaminated, wouldn't they be degraded in the wet as well as when they are dry?

    Try a different type of pad....

  11. #11
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    I live in a very dry country, so I can guarantee that I haven't ridden through any liquid (not even rain!). The only time the bike gets wet is when I hose the dust off!

    It was after I washed the bike that I noticed the brakes were greatly improved.

  12. #12
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    Quote Originally Posted by jeffscott
    Try a different type of pad....
    First time I replaced the pads, I used Shimano ones. The second time I replaced them, I used 3rd party resin pads. Both suffered the same problems.

  13. #13
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    Quote Originally Posted by johna7770
    I've just looked again really closely for any signs of leaks around the caliper or from the forks - everything looks really dry. No signs of oil anywhere.

    If the brake fluid was leaking, there would be some sort of pressure loss and the lever would start to feel spongy, right?

    Also, as I said earlier, when the brakes are wet, they still work very well. If the pads were getting contaminated, wouldn't they be degraded in the wet as well as when they are dry?
    in my case oil are leak but brake still fully functional!!! but if you rebleeding you will find loss some fluid (approx 1-2 cc.) pls. recheck your brake with my method first clean the caliper then fully squeeze the lever many time and wait for 6-12 hr. to check out if found some oil you need to go to replace cable but if not any sign of leak change your pad


    in another case try to tighten bleeding screw
    Last edited by wiwit_we; 03-08-2011 at 05:46 PM.

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