Slave Cylinder Maintenance

Discussion in 'Cycling Archive' started by Tosspot, Sep 27, 2015.

  1. Tosspot

    Tosspot Guest

    In an effort to find out what is *really* in hydraulic brakes, I have a
    very old Louise lever and calliper.

    So far, I have failed to discover how to get into the slave cylinder.

    Anyone got any pointers?
     
    Tosspot, Sep 27, 2015
    #1
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  2. Tosspot

    Clive George Guest

    Some form of Fantastic Voyage-style capsule and go up the pipe?
     
    Clive George, Sep 27, 2015
    #2
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  3. Tosspot

    Tosspot Guest

    The whole thing may be held together with a 17/18mm hex nut. I may
    order some oversize hex keys, a vice and a hammer...
     
    Tosspot, Sep 28, 2015
    #3
  4. Tosspot

    Rob Morley Guest

    What do you expect to find inside? There's just a piston with a seal
    or two. The big screw plate is probably sealed with something that
    will make it hard to remove, and impossible to restore proper function
    afterwards.
     
    Rob Morley, Sep 28, 2015
    #4
  5. Tosspot

    Phil W Lee Guest

    Normally, remove caliper then the pads and push out the piston with
    compressed air through the hose.

    Just like you do it on cars and motorcycles.
     
    Phil W Lee, Sep 28, 2015
    #5
  6. Tosspot

    Tosspot Guest


    Sez you! "Probably sealed", "impossible to restore".

    It's a bin job. I'm told the calliper pissed it's pants, so It's the
    bin. Or, I try and get it apart to find out exactly what it looks like.

    Having spoken to someone who's taken Hope callipers apart, he reckons
    the hex thing will in fact undo, and both pistons will come through the
    exposed hole.

    Then I'm going to look at the lever end :)
     
    Tosspot, Sep 28, 2015
    #6
  7. Tosspot

    Mike Causer Guest

    Yeah, but not with line-pressure. Do it with a bicycle pump or something
    else that soon runs out of puff.


    Mike
     
    Mike Causer, Sep 28, 2015
    #7
  8. Tosspot

    Rob Morley Guest

    Could just be the seal(s) that died - there's not really anywhere else
    for fluid to come out. If there's sticky crap or wear to the cylinder
    wall you might be able to clean it up and hone it through the open end
    (assuming you get to open the end).
    We had a customer who complained his (I think they were Pace) fork legs
    would come loose with normal use. There was a special seating compound
    that had to be applied to the stanchions to lock them in place in the
    crown, and as soon as you loosened the screws the compound had to be
    cleaned off and reapplied. Turned out this lad liked to fiddle with
    the screws (quite why I never discovered) - suffice it to say that his
    dad got charged for this "warranty work".
     
    Rob Morley, Sep 29, 2015
    #8
  9. Tosspot

    Tosspot Guest

    Hex keys arrive Friday, so I'll take a look. I'm not aimong to fix
    them, they must be at least 10 years old, just interested in the failure
    mode.
    Well, he learnt something. At a cost mind. I aim on doing similar,
    accept for free :)
     
    Tosspot, Sep 29, 2015
    #9
  10. Tosspot

    Tosspot Guest

    Never done it on any brake before. The pistons are really that short
    then? And presumably one has to be held in place or do the both come
    out at the same time? If one comes out before the other you're surely
    in trouble?

    I saw Mikes post on using compressed air, so presumably it might be
    worth a length of hose with a the correct adaptor on one end. Are the
    calliper threads mostly the same across manufacturers?
     
    Tosspot, Sep 29, 2015
    #10
  11. Tosspot

    Phil W Lee Guest

    Several options exist.
    Eject one piston, then put it back in just enough to seal and clamp it
    in place while you eject the other.
    Eject one, then plug the small fluid entry hole in the cylinder with a
    rubber bung while you push out the other piston (being a tiny diameter
    hole, this will need much less force than will be applied over the
    area of a whole piston).
    Jig around with packing and clamps to get each of the pistons to the
    "almost out" position at the same time, then grab and pull. Careful
    not to damage the surface of the pistons though.
    There may only be one piston, with either the caliper moving across to
    bring the other pad into contact, or the disc moving across to press
    on the other pad.
    With cars and motorcycles, I've never used an adapter - just pressed
    an air nozzle into the hole. So it leaks - with an airline, the
    volume of air is effectively unlimited, so who cares?
    I've never had a problem with the pistons flying out under pressure,
    maybe because of the leaky joint where I'm injecting air, but you can
    always put it inside a sack if it's a worry.
     
    Phil W Lee, Sep 29, 2015
    #11
  12. Tosspot

    Rob Morley Guest

    There's room to get them out without splitting the caliper (which is
    just as well as many two-piece calipers are joined-for-life and can't
    be split despite the presence of bolts that suggest otherwise, because
    they wouldn't align properly on reassembly).
    Replace the seal (if that's why you disassembled it), lubricate
    with some fresh fluid, put it back in and pop the other one.
    The conical plastic adaptor that comes with most pumps should do the
    trick.
    http://cdn.sigmasport.co.uk/product...peak-Joe-Blow-Race-Track-Pump-attachments.jpg
     
    Rob Morley, Sep 29, 2015
    #12
  13. Tosspot

    Tosspot Guest


    Living and learning. Either my Google Mojo has deserted me, or this
    isn't actually that easy to find out.
     
    Tosspot, Sep 29, 2015
    #13
  14. Tosspot

    Tosspot Guest


    Ok, application of compressed air forced one cyclinder out with a loud
    *POP*. How it goes back in is a mystery :-(
     
    Tosspot, Oct 4, 2015
    #14
  15. Tosspot

    Mike Causer Guest

    Lubricate with brake fluid and make sure you are pressing absolutely
    square-on to the cylinder. If you can get the pieces into a bench vice
    somehow that will help with the force involved and with the
    square-on-ness.

    Disclaimer: I've done car and motorcycle brake pistons this way, but
    not (yet) bicycle.


    Mike
     
    Mike Causer, Oct 4, 2015
    #15
  16. Tosspot

    Rob Morley Guest

    Something was probably stuck to make it go pop. Could just be dry
    seals. Clean piston and cylinder, inspect for wear and corrosion of the
    metal[2] and perishing of the rubber. Apply a few drops of the
    appropriate brake fluid to piston and cylinder, then gently insert the
    piston into the cylinder being sure to keep it as square as possible.
    You may find a plastic[1] tyre lever or similar helps to press on the
    middle of the piston face. When it's inserted make sure that gentle
    pressure will move the piston. To remove the other piston you'll need
    to hold the one you just fitted in place - plastic tyre lever held
    across the face of the piston with a few turns of string around the
    caliper, and blow.



    [1] I'm a fan of plastic implements when working with aluminium parts
    that could be made scrap if you slip with a screwdriver.
    [2] Judicious application of very fine wire wool can smooth minor
    surface imperfections.
     
    Rob Morley, Oct 5, 2015
    #16
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