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  1. #26
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    Whoops!

    I had the calipers off and was extending the pistons all the way to make sure they were good and clean and I went too far. I heard it "burp" and now I am definitely waiting for the bleed kit.

  2. #27
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    Summary

    I think I got the brakes working to an acceptable level. I did everything suggested in this thread and he brakes still howled and had really low power. Out of frustration I went out and repeatedly braked as hard as I could past the point of the squeal and they improved significantly.

    Here's a timeline to help anybody else troubleshoot brake problems.
    - The brakes were squealing and had low power.
    - One of the pads was warn down to almost nothing and the other was only about 50%
    - Replacing the pads seemed to help - i was headed on a vaca with the bike so I was living with it.
    - Not too many miles later the back brakes are still much worse than the front.
    - Came back to this thread.
    - Adjusted the calipers every which way - No improvement
    - Extended the pistons all the way to clean them (they seemed clean to start but nothing else was working) - No improvement
    - Extended the pistons too far and got air in the system
    - Bled the system. - no improvement
    - Put on a fresh set of pads - No improvement
    - Went out and did about 10 hard stops - Success!

    While I was wearing in the pads the back wheel was chattering and squealing loudly but by the end I cold modulate right up to a skid. I'm guessing that my old pads are OK but it's working now so I'm not going to touch it.

    I'm hoping the problem doesn't return like HalFliP but if it does I'm hoping the fix is some good hard stops.

  3. #28
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    I'm just curious, when you dropped in a new set of pads, did you ever bed them in?
    Alcohol may lead nowhere, but it sure is the scenic route!

  4. #29
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    Quote Originally Posted by HalFliP View Post
    Going to be follwing this thread now.

    Back in May I ordered new M785's for my Tallboy build. The first few rides were great and the brakes awesome. The fronts have given me no issues whatsoever.

    The rears, however, seem to have developed a loss in power/squeal as described above. I tried lightly sanding pads and rotor on the original pads, which did not help. Fed up, I purchased a set of resin pads and again, lightly sanded the rotor. Boom, good as new, better even(I like the resin better). Now, after each ride, it seems that the symptoms return and I have to repeat the sanding process each time.

    I have kept an eye out for banjo and any other leaks....nothing. Not even any spots where it seems trail dust is collecting due to oil. My hoses have been shortened and levers feel pretty firm.

    two things: Are you saying that the smallest amount of air in the system could cause these issues...??

    And, Has anyone heard of any issues with oil seeping from the pistons on these...?? Sometimes when I take the pads out to sand them, I notice a light ring on the left pad....just barely enough to see where the piston contacts the pad. It isn't enough to even drip. Normal??
    My xtr shimano brakes will leak fluid when it gets cold below about -12 C....

    Most other shimano brakes will also leak when cold....

    After about 6 months (winter here) I just fill up the reserviors....the pads will generally self clean at that leak rate.

  5. #30
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    If you are talking about the pair between the uneven wear and this set. Nope. I'm learning this hydro disk brake thing as I go. Some things I read indicate that the bedding should have happened to the rotors with the first set of pads. The problem that lead me to find the unevenly worn pair was howling brakes with low power. Can then get un-bedded? Should they be bedded every pad change even using like pads?

  6. #31
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    Quote Originally Posted by bedwards1000 View Post
    If you are talking about the pair between the uneven wear and this set. Nope. I'm learning this hydro disk brake thing as I go. Some things I read indicate that the bedding should have happened to the rotors with the first set of pads. The problem that lead me to find the unevenly worn pair was howling brakes with low power. Can then get un-bedded? Should they be bedded every pad change even using like pads?
    Bedding is the process of allowing some of the pad material to coat the rotor...

    It will happen regardless of how you bed them in.....it will just happen faster if you go out and do some hard stops...

    I live on top of a small hill maybe 100 vertical feet....so after I change pads I just ride down the hill and stop hard....I can feel the brake performance improving as I do it....then I just keep riding...

    They can get un-bedded again if you sand the rotor for example....or oil up the pads....but it is pretty hard to do if everything is working right....If the rotor starts to look shiney the bedding as been reduced....(a really long brake resulting in a blue hot rotor can do this).

    So yes bed everytime you change the pads and or sand the rotors or cook the brakes.

  7. #32
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    Wicked good info Jeffscott. I'm not sure why the previous pads didn't bed in with my attempts to stop but the symptom persisted on 3 different sets of pads until I went out and did some intentional hard braking. Do you know if cleaning the rotor with alcohol will remove the bedded pad material?

    Actually, remembering back to the first time I had the problem, it was a muddy day. I originally thought I had grass between the pads and rotors that was keeping me from stopping. I bet the type of mud was fine enough to "sand" the rotors.

    Learning, learning, learning.

  8. #33
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    Quote Originally Posted by bedwards1000 View Post
    Wicked good info Jeffscott. I'm not sure why the previous pads didn't bed in with my attempts to stop but the symptom persisted on 3 different sets of pads until I went out and did some intentional hard braking. Do you know if cleaning the rotor with alcohol will remove the bedded pad material?

    Actually, remembering back to the first time I had the problem, it was a muddy day. I originally thought I had grass between the pads and rotors that was keeping me from stopping. I bet the type of mud was fine enough to "sand" the rotors.

    Learning, learning, learning.
    I have not noticed alcohol reducing the brake performance so no I don't think a light alcohol wash would do much....

    Yes of course mud and sand can remove the layer as you suggest.

  9. #34
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    Quote Originally Posted by bedwards1000 View Post
    Do you know if cleaning the rotor with alcohol will remove the bedded pad material?
    It won't completely remove the bedded in material, no. However, it does remove a surface layer and I notice that when I give my rotors a wipe with alcohol, the first few stops are noticeably underpowered but quickly return with a hard-stop.
    Alcohol may lead nowhere, but it sure is the scenic route!

  10. #35
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    Quote Originally Posted by jeffscott View Post
    I have not noticed alcohol reducing the brake performance so no I don't think a light alcohol wash would do much....

    Yes of course mud and sand can remove the layer as you suggest.
    In many circles, folks actually suggest smearing mud on the rotor surface to expedite the bedding-in process. I've tried it and it works beautifully.
    Alcohol may lead nowhere, but it sure is the scenic route!

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