Shimano power problem- Mtbr.com
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  1. #1
    mnt bike laws of physics
    Reputation: yogiprophet's Avatar
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    Shimano power problem

    My M970 brakes have all of a sudden had a major reduction in power. It is very strange.
    When I use them for the first time in a few days, the power is very low until about 1/2 hour into a ride. Then the power is fine for a while.
    What gives?

  2. #2
    mtbr member
    Reputation: mitzikatzi's Avatar
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    Air in the lines? Flush and bleed the brakes with new oil for a start.
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  3. #3
    MEGALOMANIAC
    Reputation: Hawgzilla's Avatar
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    Yup, air in the system. Once the fluid heats up and is circulated around after riding for a little while, it expands and or the air is pushed to a dead spot where it has less of an effect on the system overall.

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  4. #4
    bikeaholic
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    Yea, it most likely just needs a fresh bleed. I would also check to see if there are any kinks in your brake lines. Sometimes even small kinks can push the fluid in-between the inner (main) hose and the outside coating which would cause a loss in power.

  5. #5
    mnt bike laws of physics
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    air?

    I would have never thought air. It just doesn't feel like when I get air in other brakes I have such as Magura. The levers on my Mags just sink into the bar and then they catch, but the power is still there. I suppose since the design is different, air could have a completely different affect. Also, with the shimano brakes, I can ride the bike an hour or even two later and the power is still there...well after the brakes have cooled down. The lever fell is not at all like the typical air squishy feel. The other mystery is that it happened in both brakes at once. I suppose the only thing I can do really is to change the oil.
    Thank you guys very much for your time and help

  6. #6
    ups and downs
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    Look for oil seeping past the piston seals on the calipers.
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  7. #7
    mnt bike laws of physics
    Reputation: yogiprophet's Avatar
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    Quote Originally Posted by rockyuphill
    Look for oil seeping past the piston seals on the calipers.
    I didn't see any.
    I wonder if the Shimano oil could just not work as well after a few years.

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