Just a quickie brake question

Stevo210
Stevo210 Posts: 196
edited October 2012 in MTB workshop & tech
Running Hope V2 brakes. Front runs a treat, back when left for a couple of days the lever goes back to the bars on the first pull. One of the pistons seems to have retreated back inside the caliper thus only contacting disc really with one pad. Easily fixed by pushing pads and realigning to centre of disc.

The Calipers are perfectly central so thats not the issue.

They are only a couple of months old, Ive bled the front to shorten the hose when fitting. Bleed the rear??

Cheers for any thoughts and help.

Comments

  • steelie600
    steelie600 Posts: 519
    Ive not a lot of experience with MTB brakes, HOWEVER I am a motorbike/car mechanic and can answer this for ya

    On the MTB brakes you have a spring to return the pads away from the disc to make them free'er running. Motorbike and car brakes drag ever so slightly, but they have an engine to overcome this drag, whereas on an mtb we dont hence the spring.

    What I suspect is happening is the pistons are so slick (yes I mean slick and not slack) in the seals that over time the spring will push the piston back into the caliper ever so slightly causing the long lever travel you speak of.

    I have no idea if this is a common occurence, but if your brakes have a nice action and nice lever feel after youve pumped them back to normal I would assume that you dont have anything to worry about.
    Idiot ^^^^^^^^^

    Ralph
  • Stevo210
    Stevo210 Posts: 196
    Thanks for your thoughts. I see what you're saying, but by simply pumping the lever it doesnt cure the problem. It just pumps up the pistons so that they are still pushing unevenly and pushing the disc over. Im sure I shouldnt have to centralise the pads/pistons before I ride.
  • 386ka
    386ka Posts: 479
    Stevo210 wrote:
    Thanks for your thoughts. I see what you're saying, but by simply pumping the lever it doesnt cure the problem. It just pumps up the pistons so that they are still pushing unevenly and pushing the disc over. Im sure I shouldnt have to centralise the pads/pistons before I ride.
    Oh, so one piston is sticky, right? Then, remove the pads, push the pistons back in, and while holding the free piston with a screwdriver (or something) in place, push gently on the lever to reveal the stuck piston. Be careful not to pop it out of the caliper! Clean it using lot of water, and if you can, lube it on the sides with brake fluid.
    Then push it back in, install the pads and wheel, and try it out! :)
    A much loved, Giant Trance X3 2010
  • steelie600
    steelie600 Posts: 519
    TBH I would pop the piston out, give it a bloody good clean with t-cut to get all the dirt off and check the seals for signs of wear, replace if necessary and GREASE the seals with RED RUBBER GREASE, dont use anything else AT ALL, red rubber grease is the best in the biz!

    Rebleed and you should be fine.
    Idiot ^^^^^^^^^

    Ralph
  • nicklouse
    nicklouse Posts: 50,675
    steelie600 wrote:
    Ive not a lot of experience with MTB brakes, HOWEVER I am a motorbike/car mechanic and can answer this for ya

    On the MTB brakes you have a spring to return the pads away from the disc to make them free'er running. Motorbike and car brakes drag ever so slightly, but they have an engine to overcome this drag, whereas on an mtb we dont hence the spring.

    What I suspect is happening is the pistons are so slick (yes I mean slick and not slack) in the seals that over time the spring will push the piston back into the caliper ever so slightly causing the long lever travel you speak of.

    I have no idea if this is a common occurence, but if your brakes have a nice action and nice lever feel after youve pumped them back to normal I would assume that you dont have anything to worry about.

    Sorry totally incorrect.
    "Do not follow where the path may lead, Go instead where there is no path, and Leave a Trail."
    Parktools :?:SheldonBrown
  • steelie600
    steelie600 Posts: 519
    I gathered that when he then said afterwards he's got a sticking caliper!

    OH and I have had pistons on monobloc Brembo's that you could push in with a feather! Hence the bit about the spring might be pushing it back in!
    Idiot ^^^^^^^^^

    Ralph
  • nicklouse
    nicklouse Posts: 50,675
    Stevo210 wrote:
    Running Hope V2 brakes. Front runs a treat, back when left for a couple of days the lever goes back to the bars on the first pull. One of the pistons seems to have retreated back inside the caliper thus only contacting disc really with one pad. Easily fixed by pushing pads and realigning to centre of disc.

    The Calipers are perfectly central so thats not the issue.

    They are only a couple of months old, Ive bled the front to shorten the hose when fitting. Bleed the rear??

    Cheers for any thoughts and help.
    Two things to do. Leave the brakes on overnight with the lever held back by a zip tie or rubber band.

    The other could be the diaphragm is sucking one piston back into the caliper so a bleed could help. Be careful to bled it correctly so as not to over fill it as that can led to other issues.
    "Do not follow where the path may lead, Go instead where there is no path, and Leave a Trail."
    Parktools :?:SheldonBrown
  • nicklouse
    nicklouse Posts: 50,675
    steelie600 wrote:
    I gathered that when he then said afterwards he's got a sticking caliper!

    OH and I have had pistons on monobloc Brembo's that you could push in with a feather! Hence the bit about the spring might be pushing it back in!
    The piston retraction on MTBs is done by the seal the pad spring has nothing to do with it.

    The pistons move in and out without the spring being there and some don't even have a spring. But use clips or magnets to keep the pads off the rotor.
    "Do not follow where the path may lead, Go instead where there is no path, and Leave a Trail."
    Parktools :?:SheldonBrown
  • steelie600
    steelie600 Posts: 519
    SO they use tapered seals just like motorbikes then?? TBH ive only ever bled some MTB brakes not stripped so havent had the pleasure yet. But cheers fer that summat else to keep in mind.
    Idiot ^^^^^^^^^

    Ralph
  • Shylock
    Shylock Posts: 98
    386ka wrote:
    Stevo210 wrote:
    Thanks for your thoughts. I see what you're saying, but by simply pumping the lever it doesnt cure the problem. It just pumps up the pistons so that they are still pushing unevenly and pushing the disc over. Im sure I shouldnt have to centralise the pads/pistons before I ride.
    Oh, so one piston is sticky, right? Then, remove the pads, push the pistons back in, and while holding the free piston with a screwdriver (or something) in place, push gently on the lever to reveal the stuck piston. Be careful not to pop it out of the caliper! Clean it using lot of water, and if you can, lube it on the sides with brake fluid.
    Then push it back in, install the pads and wheel, and try it out! :)

    Sorry to re bump but, I evidently pushed the brake lever whilst the wheel was out and now one piston seems to not be retracting. How do you push the piston back in?
  • cooldad
    cooldad Posts: 32,599
    Stick a big screwdriver between the pistons (leave the pads in - cheaper if you cause damage) and twist or lever them apart.
    I don't do smileys.

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    Parktools
  • Shylock
    Shylock Posts: 98
    Cheers!

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