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Bleeding Shimano

mountaincarrotmountaincarrot Posts: 26
edited August 2007 in MTB workshop & tech
Bleeding Shimano hydraulics:

Instructions say "Insert a 10mm block across the pads", ostensibly to "prevent piston from extending".

This is a hefty block, is there any reason for it? Why prevent the pistons from extending when the brakes are being bled? Naturally you need something in there to stop them coming right out, but the disc rotor (assuming the wheel is in) or the little thin red plastic safety clip supplied by Shimano would seem do the job just as well.

There is no reason in a car system to jack the pistons fully back in when bleeding them.

:?: So why do Shimano say this?


  • x-islex-isle Posts: 794
    The 10mm block is used when the caliper is off the frame, which is the way I bleed the system if I can't get the air out. You won'y fit a 10mm block in there when it's attached to the bike and the wheel is on.

    I put the bike in a stand, remove the caliper and let it hang vertically off the handlerbars, keeping the pipe straight (for the back you'll need to remove the pipe from the frame clamps).

    Then insert a 10mm block (I use a 10mm allen key) and then bleed the brakes. If there is too much air in the system, the lever doesn't always return back to the fully open position and the piston doesn't operate properly, so make sure you push the lever all the way back.

    Hope this helps
    Craig Rogers
  • Maybe Shimano say do it because it isn't a car brake?!!! :lol:

    They assume that you are going to bleed the brake off the bike, without pads and discs, so this is why they suggest putting something in there.

    It depends on what method you use to bleed the brake:
    (For both, it’s best to adjust the lever so it is level)
    If you use the traditional method, which is:

    1. Remove top cap at the lever
    2. Attach a hose/tube to the bleed nipple at the calliper best to have some kind of container to catch the fluid, it’s not particularly nice stuff.
    3. Undo the bleed nipple and squeeze the lever – when the lever is at the bar, hold it there, then tighten the bleed nipple. Make sure that the oil level does not fall below the metal plate in the lever or you’ll let a fat wadge of air in the censored .
    4. Repeat the process until you stop seeing bubbles in the hose attached to the calliper.

    During this method, some of the oil will end up getting pushed into the calliper so you will end up having pistons popping out.

    Now, there is another, better method that takes up far less effort and gets better results:

    1. Get a syringe and pop a tube/hose on the end. Fill it with the oil
    2. Take the top cap off the lever, and put something under it to catch the oil
    3. Attach the syringe to the bleed nipple, loosen the nipple and pump the whole syringe through until your happy that you’ve flushed all the old oil out of the system – take care not to push too hard or it’ll send a fountain of oil out the top of the lever – but it is amusing!!!!
    4. Once you’re happy you’ve got all the old oil out, close everything back off (bleed nipple etc). Then get a ziptie and tie the lever to the bar, do it as tight as is possible, this will allow any air bubbles left over to rise to the lever. For best results, adjust the lever reach so it’s all the way out, and also leave the top cap off the lever.
    5. It’s best to leave it doing this overnight, to give it time to get rid of all the air bubbles, but a couple of hours will do if you haven’t got time. Make sure you have the calliper lower than the lever, it might help to remove the calliper for this bit, and also make sure that there are no loops in the hose.
    6. When you come back to it, you might need to refill the lever with oil, then all you do is reassemble everything and ride away!
    Shut up. And ride your bike.
    Originally posted by Jon
    As Dave and Alex raced past, someone in the other group of people said 'those two are good'
  • ShadowduckShadowduck Posts: 845
    Am I the only one to misunderstand the title of this thread and expect a rant? :lol:
    Even if the voices aren't real, they have some very good ideas.
  • Naw, you're not the only one to have noticed, just the only one who has posted something unconstructive *touche* :lol: (I'm only messing)
    Shut up. And ride your bike.
    Originally posted by Jon
    As Dave and Alex raced past, someone in the other group of people said 'those two are good'
  • ShadowduckShadowduck Posts: 845
    It wouldn't be me if I let my lack of applicable knowledge get in the way of making an inane comment. :P

    I'm afraid my experience of disk brake maintenance only extends to cars and motorcycles (for which I use a MityVac; a marvellous device, but I suspect not much help for the matter under discussion).
    Even if the voices aren't real, they have some very good ideas.
  • Hi Dangerous Dave.

    I like your syringe method! Thanks for the tip, I'd like to try that next time.

    My thoughts are that Shimano say use a thick 10mm block, because possibly a thinner block (or just the disk) would maybe allow air to remain trapped inside the pistons.

    Only problem is where to get basic plastic syringe bodies. I've tried at numerous chemists in the past, and all they do is put on a pained expression and tell me to visit my GP! They say they aren't allowed to sell them. I used to know a diabetic guy who gave me a few but they got used up for oil and glue years ago.

    - The very same syringes are available in B&Q under the guise of kits to mend car windscreen chips, but they cost a lot that way!


  • PlatanoPlatano Posts: 77
    Shimano have a kit that makes bleeding very easy although it is quite expensive for what it is.

    Bleed Kit
  • Ta.

    I found syringes in for 37p. Cheaper than Shimano I guess!

    I also found the model shop where i work has some in so i'm away now.

  • Your welcome!

    Remember to do the ziptie to the bar thing tho!

    (pushing hard on the syringe is also amusing 8) )

    You can also use the ziptie method any time you feel them getting squishy.

    May have to visit that place myself for syringes, I've ruined all of mine... !
    Shut up. And ride your bike.
    Originally posted by Jon
    As Dave and Alex raced past, someone in the other group of people said 'those two are good'
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