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  1. #1
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    Hope uneven disc brake pad wear

    Hi. I wear through my back brakes (shimano xt disc) way too fast. Burn through rear pads at about a rate of 5:1 relative to front. i don't think i use an excessive amount of rear brake relative to front. interestingly, one side of the pad seems to be wearing out much more quickly than the other.

    brakes are a little sticky sometimes when first engaging. related? fix?

    do you think it's some kind of alignment issue? how to fix?

    thanks for your thoughts and help.

    frisco

  2. #2
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    Reputation: Bikinfoolferlife's Avatar
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    What brakes?
    "...the people get the government they deserve..."
    suum quique

  3. #3
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    He wrote Shimano

    If one is wearing faster than the other, then either you're caliper (rear) is not centered around the rotor, or your rotor is bent to one side, or your piston is not retracting properly on one side.

    It might be something totally different like a bad hub or whatever, but it is probably a relatively easy to fix brake issue.

  4. #4
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    Yeah, he already posted in tooltime and I suggested he post here, but he did add that, sorry. I assume Shimano doesn't offer mechanical disc brakes? I don't keep up with all the available models...
    "...the people get the government they deserve..."
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  5. #5
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    shimano xt hydraulic disc. i found a page on the park website on how to center the calipers. if it's an improperly retracting piston, how do i diagnose and fix?

  6. #6
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    Quote Originally Posted by cardozo
    shimano xt hydraulic disc. i found a page on the park website on how to center the calipers. if it's an improperly retracting piston, how do i diagnose and fix?
    You can remove the caliper and the pads, and push the pistons closed. The pull the brake lever while holding one piston closed and open it up a little. One or two squeezes. The push it closed again. Then do the other side. I usually spray some silicon on the pistons and clean them to get rid of the grime the prevents them from retracting properly. This works the pistons through their range and frees them up.

    I have the same brakes and if I do this once every 6 months or so they continue to work flawlessly. Remove the pads so no oil gets on them. I wrap a thin rag around the caliper and use pliers to close the pistons. This has worked well for me, and I have not damaged anything in the process.

    The pistons should close pretty easily, so you don't need to squeeze hard. The closer you are to the center of the piston face the better.

    Good luck.

  7. #7
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    "if it's an improperly retracting piston, how do i diagnose and fix?"

    Piston problems will become apparent once you try operating the brake after having aligned the caliper. It is this very reason that I stress, whenever asked, the importance of aligning a caliper, minus pads, to the rotor, rather than the old 'loosen bolts, pull lever, tighten bolts' procedure - if the caliper has uneven piston operation, this method will mask it and provide a maligned caliper.

    So, pull those pads, push the pistons back so they're flush with the caliper interior and spend a good few minutes, paying very close attention to the spacing either side of the rotor and at each rotor slot, and get that caliper perfectly positioned over the rotor. When it is, then replace the pads. Now, pull the lever a few times until the pistons have all been activated. When you pull the lever now, watch the rotor carefully...does it appear to flex or move when the pads grab it? If it does, then you have uneven movement of the pistons. Whatever, give the wheel a spin and listen out for the pads dragging the rotor. A lzy piston(s) can be woken up by holding the free-moving piston(s) steady while pulling the lever. Check out this Hope video...



    Give all that a crack and see where it gets you.
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  8. #8
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    thanks guys, i'll work on it this weekend

  9. #9
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    it looks to me like it's a piston problem on one side. it doesn't seem to retract well. i got it all centered with new pads and it seems kosher, then pump the brakes and one side keeps rubbing a bit. took everything out, cleaned and reassembled and the problem repeated itself. spoke with a guy at the lbc and he said the brake should probably be dissembled and the piston sanded down a bit. does this sound right to the folk here?

    thanks again

  10. #10
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    "spoke with a guy at the lbc and he said the brake should probably be dissembled and the piston sanded down a bit. does this sound right to the folk here?"

    Disassembled, yes, but sanding down pistons? Don't let this bloke anywhere near your brake, or the rest of your bike for that matter.

    I don't believe that Shimano are particularly good for serviceability. If the brake/bike is new then you have the option to return it for a replacement. If it isn't, then you're going to get wise. If the piston seal has failed - the primary cause of piston seizure - then it has to be replaced. There's a chance that the seal is clogged up with dirt/brake dust, in which case you can pop the piston out (use a plastic tyre lever to hold the good piston in place while you carefully pump the dodgy one out), then the seal, and clean the piston bore, seal and piston with a cotton bud and some mineral oil. Reassemble, bleed and see how it all works.

    Which model XT are they, by the way? How old? How many miles? Have they always been this way? Service history?
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    What luck for rulers, that men do not think - Adolf Hitler

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