Resetting Pistons on XT hydros-
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  1. #1
    Dain Bramaged
    Reputation: Dijridoo's Avatar
    Join Date
    Jan 2004

    Resetting Pistons on XT hydros

    I recently did full bleeds (first time) on my 2001 XT hydros. At the same time I installed new pads (Summit generic XT replacements). They are painted orange, so I filed the paint off the vertical edges to allow them to fit better. My old pads must have been REALLY worn down, since there wasn't much clearance between pads & rotors after installing the new ones. I did a few trips round the block to try to help bed the pads & rotors and make sure everything worked OK. Then it got really cold and I hadn't been able to ride that bike since the bleed.

    OK here's my question: yesterday I took it to work and noticed that it seemed like I was pedaling a frigging concrete tank (granted, I've been commuting on a skinny-tired fixed gear during the cold snap, and now riding the Slayer with Mammoth wheels and 2.4 tires is quite the change). When pulling up to the door my front brake was squealing like a pig. I noticed when inside that both wheels would not spin freely more than 3-4 revolutions due to rotor drag. No wonder it was hard to pedal! The rotors looked centered, but just ZERO pad clearance. I think it's becausethe pistons aren't retracting far enough.

    I really don't want to have to open the system and screw around with bleeding again. I was wondering if the following would work - remove the pads, adjust the bars to level the reservoirs, open the reservoir caps, push the pistons as far back into the calipers as I can, then close the caps and reinstall the pads. Is this a viable solution, or might there be another reason the pistons aren't retrating (or are they possibly gummed up somehow)?

    Sorry for the long winded question but I'm pretty new to this hydraulic thing.

  2. #2
    simply me
    Reputation: bostonkiwi's Avatar
    Join Date
    Jan 2004
    Did you install the new pads then bleed the brakes or the other way round. If you bled first with worn pads then istalled the new ones you may have too much fluyid in the system in which case doing what you suggest will help.

    It does sound like the pads are a tight fit, they may need a bit of wearing down to give the rotors a bit of space...

  3. #3
    Dain Bramaged
    Reputation: Dijridoo's Avatar
    Join Date
    Jan 2004
    No - I installed the new pads first. I tried my own suggestion of uncapping the system & pushing the pistons back a bit. Seems to have worked OK. I just get a little skeptical about how this cold affects things involving fluid. It's been between +5F and -44F over the last few weeks.

  4. #4
    Yay! Bikes !
    Reputation: Nick.'s Avatar
    Join Date
    Dec 2003

    You are on the right track.

    I don't think you even have to open up your levers. It is an open design and allows for expansion of fluid. Whenever I change brake pads on my XTs I do the following;

    - pull the wheel
    - pull the old pads
    - use a tire lever (plastic) to slowly push all the pistons back into the caliper. If you push too quickly you'll see the other pistons move out as you push one in.
    - install new pads, tighten that bolt thing and re-install the cotterpin

    Throw your wheel back on and pump your lever a few times until the pads reset. Done.

    I've been using the green EGB pads and like them better than the stock Shimano pads.
    I've used generic unscented mineral oil for two years with great results. MUCH cheaper than the Shimano fluid which is, as far as I can tell, unscented mineral oil with red coloring added.

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