what've i done to my brakes?

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  • what've i done to my brakes?
  • Premier Icon Onzadog
    Subscriber

    Odd one. What exactly did you do? Did you push the pistons back? Silly question but did pushing one back force another one out?

    Premier Icon Northwind
    Subscriber

    Dales_rider will probably explode but if they were spongy before and dead now, it suggests they had air already hanging around in the system and it’s got somewhere you don’t want it. (pushing back the pads moves a lot of fluid fast so though logically it shouldn’t cause air to get in- since you’re pushing fluid up into the reservoir- in practice unpredictable things can happen with bubbling, pushback etc.)

    Have you tried the bodger’s classic of tying back the levers and leaving them for a while? Not really a fix in my book but a useful diagnostic (if they start working then it’s definitely air)

    People bleed too often when it’s not the problem, but, sometimes it is.

    thanks for the replies.
    when i took the pads out i pulled the lever to make sure the pistons were coming out,they did,so pushed them back in,popped in the new pads and …nowt

    just changed the pads on my mono m4’s and now there is zero pressure – nothing. stuck the new pads in as they were on the low side and it felt a bit spongy but now there’s nowt.
    what sort of bother have my fat fingers got me into now?

    snaps
    Member

    Have you made sure the pistons are moving the pads against the disc at the same time?
    [video]http://www.youtube.com/watch?v=akIWGqEE0PY[/video]

    Premier Icon Northwind
    Subscriber

    That wouldn’t cause this problem- it reduces effectiveness but won’t leave it powerless. Worth doing on general principles mind.

    Rockhopper
    Member

    1. The pads wouldn’t cause the initial spongy feeling – thats due to air in the system.

    2. When you pulled the lever without the pads in you have popped one of the pistons right out and let a load of air into the system.

    thanks again for the replies,much appreciated.
    i am a ham-fisted buffoon who really should know better than messing with stuff i know knack all about.i’ll have another look in the morning and try to see where i muffed up
    cheers

    Premier Icon Northwind
    Subscriber

    Rockhopper – Member

    2. When you pulled the lever without the pads in you have popped one of the pistons right out and let a load of air into the system.

    Ooh, that’s not likely, takes a bit of work to get them back in unless you’re freakishly lucky but even then it ought to be noticable… But then if you’re not familiar with brakes, maybe not. OP, did you see any fluid escape?

    nope,no fluid at all and pistons pushed back in easily.

    time to bin the old faithfulls?

    Aristotle
    Member

    Air has possibly been pushed up into the master cylinder (something that is rarely mentioned in fluid changing/bleeding guides).

    If so, it can take a while to displace it.

    Take the reservoir cap off and, quickly & repeatedly, squeeze/release the lever part-way back. you may see small bubbles rising through the reservoir. Stop and repeatedly tap the master cylinder and hose area with the (soft/rubbery) handle of a large screw-driver. Resume squeezing the lever.

    Keep doing it until the bubbles -eventually- stop. the lever should now have firmed-up.

    coatesy
    Member

    As an educated guess, i’d suspect you had the bike upside down whilst working on it, allowing air from the reservoir into the system, if so, a bleed should sort it.

    kja78
    Member

    Surely it’s just that you pushed the pistons back in, you just need to pump the levers a few times til the pads contact the rotors then it’ll be fine.

    jdwafc
    Member

    Strip all system, recheck & clean (around pistols) reassemble, bleed system, to align fresh pads have caliper bolts loose a little, put a playing card between each pad & disc, now a firm grip on brake handle (keep hold) to centre caliper, tighten bolts up remove card, clean disc properly (use disc cleaner) test, check for leaks and your off.
    Also don’t touch ya pads, if you do, sand them a little and use disc cleaner.

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