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Bleeding Shimano XT Brakes

boneyjoeboneyjoe Posts: 369
edited September 2011 in MTB workshop & tech
Had my first go at this last night for the rear brake (using the "kit", ie bottle + tube method), and while the result isn't too bad, the feel is still a bit squishy compared to the front brake - lever depresses about 1cm more than the front.

Tried pumping the brake lever numerous times (a few bubbles came out at first but not any more), and had the same result for opening and closing the bleed valve on the brake while pulling the lever.

Any advice would be much appreciated! Thks.
Scott Scale 20 (for xc racing)
Gary Fisher HKEK (for commuting)

Posts

  • Although I haven't done it myself, others bleed them from the bottom up, basically just firing a syringe full of fluid up through the system. Seems more sensible, since bubbles will always want to go upwards!

    There's some pointers at

    http://singletrackworld.com/forum/topic ... rake-bleed
    2011 Canyon XC 8.0 (Monza Race Red)
    1996(?) dyna-tech titanium HT; pace RC-35's; Hope Ti Hubs etc etc
    Bianchi Road Bike
  • Thanks. Yes, I saw a couple of vids on this and have been thinking about it. Might give it a try this evening if I can get the right bits together!
    Scott Scale 20 (for xc racing)
    Gary Fisher HKEK (for commuting)
  • I would say there must still be some air in the system

    Tap along the line with something plastic. Just keep adding fluid even if it means completely replacing all the fluid that's in the system currently and make sure the reservoir doesn't run dry.

    The lever will be really stiff when all air is out
    "Why have that extra tooth if you're not using it?" - Brian Lopes

    Votec V.SX Enduro 'Alpine Thug' 2012/2013 build

    Trek Session 8
  • Dirtydog11Dirtydog11 Posts: 1,621
    I've got two different sets of Shimano brakes and found that the quickest/easiest way is to push the oil through from the caliper end with a syringe, as its only mineral oil you can get away with just putting a plastic bowl under the lever (master cylinder) to catch the expelled (overflowing) oil, a quick wipe round with a tissue and jobs done.

    *Note*
    You will experience uneven lever travel if the pistons/calipers aren't centered over the disc, so do they feel spongy or is it just uneven lever throw?

    If they feel spongy bleed again, if the lever travel is uneven then reset and centralise the offending piston.
  • Did you bleed them while still on the bike? I always drop the rear calliper off and get it as low as possible with the hose as vertical as possible. This way there is much less chance of air getting trapped in the system and you get a much firmer lever as a result.
  • Thanks guys. Tried the syringe system last night, but with pretty much the same result unfortunately. Though my equipment wasn't the best, so it may be there is still some air getting in. Will try centering the pistons and, if that doesn't help, will then take the rear caliper off the bike and get it as low as possible for one last go. Thks again for the advice.
    Scott Scale 20 (for xc racing)
    Gary Fisher HKEK (for commuting)
  • jaysonjayson Posts: 4,606
    Try gettin a cable tie or somethin similar and tyin the brake lever back to the bar with it and leave it like that over night, leave the reservoir cover off and u should see any air bubbles in there the next day ready to purge and then top back up with fluid.
  • boneyjoeboneyjoe Posts: 369
    edited September 2011
    Still grappling with this unfortunately. Got the brake lever feeling really firm with mister p's vertical brake line method, but on putting the brake back in place the pressure dropped dramatically. Then noticed, on pumping the brake lever (the first 10 or so times after topping and closing the reservoir), that there is oil leaking out the top of the reservoir. I'm guessing this isn't normal, is it? The overflow stops after 10 or so pulls on the lever, but I'm guessing this should be a sealed unit with no overflow once the screws are tightened?
    Scott Scale 20 (for xc racing)
    Gary Fisher HKEK (for commuting)
  • That is not normal no. Is it coming through the gap between top cap and reservoir body? You have put the rubber diaphragm back in haven't you? Sorry I know that may sound a little patronising but you have to check all possibilities.
  • Thanks mister p. Yes, the diaphragm is back in place. I'm guessing I probably need either a new diaphragm or top cap to get it sealing properly again?
    Scott Scale 20 (for xc racing)
    Gary Fisher HKEK (for commuting)
  • It does sound that way yes.
  • Thanks for confirming mister p. Think its back to the lbs on this one, but at least we gave it a shot! Have a good day, and enjoy the great weather if you're in the UK.
    Scott Scale 20 (for xc racing)
    Gary Fisher HKEK (for commuting)
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