Disc brake suddenly locked up

julianhj
julianhj Posts: 27
edited August 2015 in MTB workshop & tech
I have a 2010(?) Cube Ltd Race with Formula RX brakes. I used my bike for the first time in a few months this morning. I checked everything over before setting off - all good. I rode a mile or so to my LBS, then on for another mile or so in to town. After a quick errand at the bank (took the bike in with me) I noticed the rear wheel was locked up. I went outside, had a closer look and the brakes were almost fully on. I tried the lever and it was extended at it's normal position; there was very little movement as the pads were already touching the disc.

I got the bike home (took the rear caliper off to get back) and had a Google. I took the pads out, checked that the lever was moving both pistons (it appeared to be), then eased the pistons back with a screwdriver. I didn't use too much pressure, as I didn't want to cause any damage. I put the pads back in and the pistons have only retracted as far as shown in the photo. The disc is a little thicker than that gap, so the pads need to be about twice as far apart I'd guess.

davr5kdq.jpg

Am I not using enough pressure to push the pistons back? Is there a fault elsewhere? I'm assuming that something has gone wrong somewhere for the pistons to suddenly fail to release.

Can anyone point me in the right direction in terms of a DIY fix, or is this a job for the chaps at my LBS?
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Comments

  • zx6man
    zx6man Posts: 1,092
    The pitons should go all the way back I reckon (well, on my motorbike they do). Chances are you need a bit more pressure
  • CitizenLee
    CitizenLee Posts: 2,227
    Try a ghetto bleed on it... zip tie the brake lever back to to your bars and leave it over night. I don't know anything about the science behind why it works but I've done it for years and it does make brakes feel better ;)
    Current:
    NukeProof Mega FR 2012
    Cube NuRoad 2018
    Previous:
    2015 Genesis CdF 10, 2014 Cube Hyde Race, 2012 NS Traffic, 2007 Specialized SX Trail, 2005 Specialized Demo 8
  • cooldad
    cooldad Posts: 32,599
    Lever them back properly. Leave the pads in so you don't damage the pistons.
    I don't do smileys.

    There is no secret ingredient - Kung Fu Panda

    London Calling on Facebook

    Parktools
  • The Rookie
    The Rookie Posts: 27,812
    Totally the wrong way round, that advances the pads, nothing like bleeding AT ALL.

    Check to see what happens if you push each piston in in turn, if one can go in further while the other comes out, then it sounds like for some reason the system is overfilled, be it with fluid or air, so a following the correct bleed/fill procedure may well sort it.
    Currently riding a Whyte T130C, X0 drivetrain, Magura Trail brakes converted to mixed wheel size (homebuilt wheels) with 140mm Fox 34 Rhythm and RP23 suspension. 12.2Kg.
  • cooldad wrote:
    Lever them back properly. Leave the pads in so you don't damage the pistons.

    Please excuse my ignorance, but what's the best technique for this?
  • cooldad
    cooldad Posts: 32,599
    The Rookie wrote:
    Totally the wrong way round, that advances the pads, nothing like bleeding AT ALL.
    Presume you are referring to the post before mine?
    Just to save confusion.
    julianhj wrote:
    cooldad wrote:
    Lever them back properly. Leave the pads in so you don't damage the pistons.

    Please excuse my ignorance, but what's the best technique for this?

    Stick a big screwdriver between them and twist like a key.
    I don't do smileys.

    There is no secret ingredient - Kung Fu Panda

    London Calling on Facebook

    Parktools
  • would reccomend using something like a tyre lever, not a screwdriver.
  • nicklouse
    nicklouse Posts: 50,675
    julianhj wrote:
    cooldad wrote:
    Lever them back properly. Leave the pads in so you don't damage the pistons.

    Please excuse my ignorance, but what's the best technique for this?
    press on the BACK of the opposite pad.

    saves the pads and the calipers.

    so you are pressing on 2 pads which are pressing on a piston.
    "Do not follow where the path may lead, Go instead where there is no path, and Leave a Trail."
    Parktools :?:SheldonBrown
  • The Rookie
    The Rookie Posts: 27,812
    cooldad wrote:
    The Rookie wrote:
    Totally the wrong way round, that advances the pads, nothing like bleeding AT ALL.
    Presume you are referring to the post before mine?
    Yup........
    Currently riding a Whyte T130C, X0 drivetrain, Magura Trail brakes converted to mixed wheel size (homebuilt wheels) with 140mm Fox 34 Rhythm and RP23 suspension. 12.2Kg.
  • cooldad
    cooldad Posts: 32,599
    would reccomend using something like a tyre lever, not a screwdriver.
    I have a really big screwdriver.
    I don't do smileys.

    There is no secret ingredient - Kung Fu Panda

    London Calling on Facebook

    Parktools
  • The Rookie
    The Rookie Posts: 27,812
    Avid travel spacers are quite good, as are decent table knives, Kitchen knives are a bit of an H and S risk though.......
    Currently riding a Whyte T130C, X0 drivetrain, Magura Trail brakes converted to mixed wheel size (homebuilt wheels) with 140mm Fox 34 Rhythm and RP23 suspension. 12.2Kg.
  • I use a cone spanner.
  • julianhj
    julianhj Posts: 27
    Well, it's happened again.

    I've not used the bike this year as I prolapsed a disc in my lower back at the start of the year. I've just got the bike out to give it a service and check that everything is working properly before starting to ride again, and the rear wheel is totally locked, no travel on the lever at all.

    Is this a common issue? I've never really got on that well with these brakes.
  • The Rookie
    The Rookie Posts: 27,812
    Sounds like the pistons are sticking just enough to prevent retraction.

    With the wheel and pads out, pull the lever gently to push the pistons out, clean round the piston with brake fluid, push back in and repeat.
    Currently riding a Whyte T130C, X0 drivetrain, Magura Trail brakes converted to mixed wheel size (homebuilt wheels) with 140mm Fox 34 Rhythm and RP23 suspension. 12.2Kg.
  • FishFish
    FishFish Posts: 2,152
    Avid travel spacers are quite good, as are decent table knives, Kitchen knives are a bit of an H and S risk though.......

    Agreed with the Avid spacer. I was showing off to my neighbour on the same topic and belted the top of the spacer to maximise the pressure on the pistons. Course it got stuck!
    ...take your pickelf on your holibobs.... :D

    jeez :roll:
  • julianhj
    julianhj Posts: 27
    I've had a go this morning - the lever is totally rigid, the pads are clamped tight to the disc, no reasonable pressure is getting anything shifted. Time for LBS I think...
  • Antm81
    Antm81 Posts: 1,406
    I've had a go this morning - the lever is totally rigid, the pads are clamped tight to the disc, no reasonable pressure is getting anything shifted. Time for LBS I think...


    Possibly seals allowing moisture in? My elixirs used to do this, used to have to let a little fluid out of the bleed port on the caliper.
  • The Rookie
    The Rookie Posts: 27,812
    Your money, but I'd try cleaning the pistons first....
    Currently riding a Whyte T130C, X0 drivetrain, Magura Trail brakes converted to mixed wheel size (homebuilt wheels) with 140mm Fox 34 Rhythm and RP23 suspension. 12.2Kg.
  • dodgy
    dodgy Posts: 2,890
    Sounds like corrosion in the pistons, they're not going back in due to the friction caused by the corrosion.
  • cooldad
    cooldad Posts: 32,599
    Hardly sudden. Bikes don't like being left unused. Things corrode and seize up.
    I don't do smileys.

    There is no secret ingredient - Kung Fu Panda

    London Calling on Facebook

    Parktools
  • The pads are stuck because of moisture absorbed into the system.
    Most will not believe it, but even the brake hose is susceptible to allowing moisture into the system.

    The problem you experience even occurs in brand new old stock bicycles when taken out of the box to build.
    It has absorbed water and is now overfilled.

    Slightly loosen the fill hole and press pistons back until they are fully retracted, tighten up fill cap.
    Wrap a rag around the lever near the fill hole to capture extra fluid.
    If they are more than a couple of years old then a full flush and bleed is a better option as the fluid now has serious contamination and if a lower level brake may lead to piston or caliper corrosion.
  • The Rookie
    The Rookie Posts: 27,812
    What a load of tosh, how does moisture get into a sealed system? and besides when it does the volume of fluid actually reduces initially, not increases, that myth has been buried several times on here before, stop trying to resurrect the dead!
    Currently riding a Whyte T130C, X0 drivetrain, Magura Trail brakes converted to mixed wheel size (homebuilt wheels) with 140mm Fox 34 Rhythm and RP23 suspension. 12.2Kg.
  • Antm81
    Antm81 Posts: 1,406
    What a load of tosh, how does moisture get into a sealed system? and besides when it does the volume of fluid actually reduces initially, not increases, that myth has been buried several times on here before, stop trying to resurrect the dead!

    Apart from the fact it happened with mine every time they were left in a moist environment, but you can't accept anybody else's opinion or accept the fact that something you think can't happen, might happen A sealed system is only as good as the seals it uses.
  • The Rookie
    The Rookie Posts: 27,812
    You haven't shown it was moisture getting in, funnily enough a moist environment is usually hot, also moisture encourages oxidation as well...

    If it's not sealed why isn't liquid and the pressure you say is causing the problem leaking out as well?
    Currently riding a Whyte T130C, X0 drivetrain, Magura Trail brakes converted to mixed wheel size (homebuilt wheels) with 140mm Fox 34 Rhythm and RP23 suspension. 12.2Kg.
  • Antm81
    Antm81 Posts: 1,406
    You haven't shown it was moisture getting in, funnily enough a moist environment is usually hot, also moisture encourages oxidation as well...

    If it's not sealed why isn't liquid and the pressure you say is causing the problem leaking out as well?

    So what would cause it then?

    Wouldn't that depend on how much moisture was absorbed and the space it could take up within the system.

    Even if it's not moisture it's fluid expansion anyway. How else do you explain letting a small amount of fluid out freeing up the Pistons and allowing them to retract.
  • The Rookie
    The Rookie Posts: 27,812
    Fluid expansion due to heat, these cases are pretty much all reported at the start of summer.
    Currently riding a Whyte T130C, X0 drivetrain, Magura Trail brakes converted to mixed wheel size (homebuilt wheels) with 140mm Fox 34 Rhythm and RP23 suspension. 12.2Kg.
  • Antm81
    Antm81 Posts: 1,406
    Fluid expansion due to heat, these cases are pretty much all reported at the start of summer.


    Possible but on my elixirs they'd lock when're bike was kept in the shed in winter but in the house during the same time of year it didn't happen. Surely if it was due to heat the fluid in those would of contracted giving greater lever travel rather than no lever travel and the Pistons pushed out on to the rotors?

    In either case the suggested remedy would have the same effect so your argument isn't entirely relevant.
  • The Rookie
    The Rookie Posts: 27,812
    If the system is overfilled due to a poor bleed technique (very common with Avid's) then it can cause all sorts of issues anyway. Organic pads swell when moist for example, so with no 'give' in the hydraulic system due to an overfill that can cause issues.
    Currently riding a Whyte T130C, X0 drivetrain, Magura Trail brakes converted to mixed wheel size (homebuilt wheels) with 140mm Fox 34 Rhythm and RP23 suspension. 12.2Kg.
  • You haven't shown it was moisture getting in, funnily enough a moist environment is usually hot, also moisture encourages oxidation as well...

    If it's not sealed why isn't liquid and the pressure you say is causing the problem leaking out as well?

    Differing molecule size and the well known fact that dot fluid is hydroscopic, that means that it attracts water.
    Try filling a dry system with water and see how the seals hold.

    This is a VERY well known effect in both the motobike and automotive world.
    Water CAN make it's way into lines through the wall, well proven and the reason why brake fluid bottles use a special plastic to help combat this.
    Moisture DOES make it's way past the rectangular seals in the calipers.
    Shimano brakes do not suffer from this problem, only DOT systems.

    This has not been thoroughly debunked on these forums, only your incorrect and misinformed posts denying that it exists.

    Do a bit of research.
  • The Rookie
    The Rookie Posts: 27,812
    Classic fail, Motorbikes (mostly) and cars run open systems and bike srun closed sealed systems, so cars and bikes absorb through the ventilation, this has breen covered on here dozens of times before, also initially absorbing water REDUCES the volume, not increases it, debunking the silly theory you espound only you are chossing to ignore it.
    Currently riding a Whyte T130C, X0 drivetrain, Magura Trail brakes converted to mixed wheel size (homebuilt wheels) with 140mm Fox 34 Rhythm and RP23 suspension. 12.2Kg.