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Brake pad fitting issue

DeejDeej Posts: 3
edited November 2013 in MTB workshop & tech
Hi all. Firstly I'm a relative bumpy, but replacing a set of pads on my Formula R1 brakes is (or should be) within my capabilities. However, I'm encountering a problem. When I fit the pads in the rear calliper, I can't get them back on the disc.....not enough space between to do this. I've pushed the pistons as far back into the calliper as possible, but still the same problem. They're the right pads (front calliper was an easy change). Wonder what the possible issues might be.....?
deej

Posts

  • nicklousenicklouse Posts: 50,675 Lives Here
    Sounds like you have too much fluid in fussy stem due to an incorrect bleed.carefully let some outdo you. An push the pistons fully home.
    "Do not follow where the path may lead, Go instead where there is no path, and Leave a Trail."
    Parktools :?:SheldonBrown
  • russyhrussyh Posts: 1,375
    nicklouse wrote:
    Sounds like you have too much fluid in fussy stem due to an incorrect bleed.carefully let some outdo you. An push the pistons fully home.


    I had exactly the same pro blem on my last bike. Did this myself and bobs your uncle, fanny is you aunt.
  • DeejDeej Posts: 3
    Thanks gents......will give it a go!
    deej
  • The RookieThe Rookie Posts: 27,803
    Don't get the released fluid on the new pads though.........
    Current steed - Whyte T129, 2013 frame, mongrel Revelations, Giant dropper, Stans S1 wheelset. 12, Magura Trail Sport brakes, 1x11. 12.8Kg
  • That's a part answer only.
    The reason that there seems to be too much fluid in your system is that it has absorbed water.
    Think about it, there was enough room for pad clearance when they were new.

    Just letting a bit out is just a band-aid, the real answer is to flush and bleed.
    Leaving the now contaminated fluid in there will lead to all of the horror stories you here about brakes with pads rubbing/ not retracting enough and stuck pistons.

    Remove pads, pump pistons out enough until you can get in there and clean them with some isopropyl alcohol, flush and bleed.

    The single biggest cause of these brakes getting a bad rap is from not regularly flushing them or using wrong fluid.
  • Where has the water come from?

    Op doesn't mention having bled the brakes.

    I'd say if no bleeding has been done you need to push the pistons home harder.
  • The RookieThe Rookie Posts: 27,803
    That's a part answer only.
    The reason that there seems to be too much fluid in your system is that it has absorbed water.
    Think about it, there was enough room for pad clearance when they were new.

    Just letting a bit out is just a band-aid, the real answer is to flush and bleed.
    Leaving the now contaminated fluid in there will lead to all of the horror stories you here about brakes with pads rubbing/ not retracting enough and stuck pistons.

    Remove pads, pump pistons out enough until you can get in there and clean them with some isopropyl alcohol, flush and bleed.

    The single biggest cause of these brakes getting a bad rap is from not regularly flushing them or using wrong fluid.
    Never heard so much baloney in all my life.....water can't get into a bike system (which is sealed by the diaphragm from the air) without some sort of a leak, it's not like a car system which is vented to atmosphere, so moisture can enter the fluid through the vent.
    Current steed - Whyte T129, 2013 frame, mongrel Revelations, Giant dropper, Stans S1 wheelset. 12, Magura Trail Sport brakes, 1x11. 12.8Kg
  • Car systems are not vented to the air.
    They have a membrane under the cap just like your bike brakes.

    The water is absorbed through the seals from the atmosphere, just like a small amount of brake fluid always gets past the seals and keeps the pistons lubed.

    If your system has pumped up, you either have air in the system or water.
    If there is air you will have an inconsistent lever and possible loss of of lever altogether sometimes.
    If there is water all that happens to make you notice is that you can't fit your new pads in just as the OP has noted.

    This is why shimano developed their own proprietary mineral fluid that is not hygroscopic so it never succumbs to this problem.

    Sorry mr Rookie, you'll never get a job in our workshop.

    OP, flush your brakes and be rewarded with long lasting well functioning brakes or take the shortcut and slowly but surely destroy them and become one of the many complainers about censored brakes that abound on this forum.
  • Clunkers, the fact that the OP does not say that the system has been bled means that for the original pads to have fit in there, there had to be less volume of fluid in the system, therefore confirming my diagnosis.

    This is such a common thing seen on the work bench, usually a bike that is not ridden much and probably has just worn out its first set of pads.

    If not done properly, the next time you see the bike is when the pads are worn out again or the they won't retract or or rub and the best thing to do then is to turf them and fit some shimano's.

    This is because the pistons / bore will now have corroded and the seals degraded, it is now junk.
    Even if just the pistons and seals need replacing, by the time you do this, parts plus labour make up a significant portion of simply bolting on new shimano's that nearly very customer just gets the new ones.

    All systems using DOT fluid will suffer from this to a more or less degree.
  • cooldadcooldad Posts: 32,599
    This is why shimano developed their own proprietary mineral fluid that is not hygroscopic so it never succumbs to this problem.

    Shimano invented mineral oil?

    Sorry mr Rightarmbad, you'll never get a job in our workshop.
    I don't do smileys.

    There is no secret ingredient - Kung Fu Panda

    London Calling on Facebook

    Parktools
  • There's only one thing confirmed here.....
  • No mate, shimano developed their own proprietary mineral oil as they wanted control over water absorbtion, interaction with the rectangular seals which control pad movement and the highest boiling point of any fluid used on push bikes.
    That's why they don't require yearly flushing as any DOT based system does.
    You only really need to change it when it starts to look a bit dark through contamination from wear of the internals.

    They understood early on in the piece the limitations of using normal dot fluid in such a small volume system with a small resevoir and relatively large seal exposure area for the total volume of the system that dot systems would be difficult.
    As have a couple of other companies that use a mineral oil of some fashion.
    Next year some of these will use shimano fluid under licence as it is simply the best for low maintainence.

    The lack if knowledge of how braking systems operate is simply astounding, leading to a bunch of old wives tales propagated by a bunch of people that have no idea.

    99% of people have no idea how the pads self adjust for wear and believe it is some complicated thingy that happens in the master cylinder.
    They follow ritualised methods of bleeding instead of understanding how the systems work and knowing the why of the different methods applied to different products.

    Amazing, simply amazing.
    You attack the only respondent to the thread that explains the exact mechanisms operating and how to treat it.

    How can you believe that somehow a system that was working fine but can't fit new pads has magically grown new extra brake fluid to make it too full?
    And you think my moisture explanation is far fetched!!!!!!

    Go back to school and learn a bit of logic.
    And for frocks sake stop dishing out info that will damage other people's gear.
  • I don't think there is magically more fluid in there, I think the pistons were not retracted enough.

    I've not changed the dot fluid or bled my brakes in 5 years of owner ship and 1,000s of miles in all weathers and gunk. They work just fine still and are the same make as the op's
  • cooldadcooldad Posts: 32,599
    Rave rant whine etc...
    Not sure who you're aiming your comments at - maybe be more specific. I have Shimano and DOT based brakes, never had problems with any of them.
    Using both proprietary and aftermarket fluids.
    I think you're overthinking it.
    I don't do smileys.

    There is no secret ingredient - Kung Fu Panda

    London Calling on Facebook

    Parktools
  • The RookieThe Rookie Posts: 27,803
    Car systems are not vented to the air.
    They have a membrane under the cap just like your bike brakes.
    Not on any of the 6 cars in my family or any I've ever owned or any of my current employers cars or any of my previous employers cars (I work as a development engineer for an automotive OEM and have worked for other OEM's and consultantcys for over 20 years), so yet more cleaning of porkines....

    Mineral oil is less hydroscopic, but has a lower boiling point in the first place, noting that when DOT first absorbs moisture it actually reduces in volume (like dissolving sugar in water reduces the volume - I remember doing that during my third year) it's only at higher concentrations does volume increase.

    All in all glad I won't get a job in your (Halfords? you fit the stereotype) workshop.
    Current steed - Whyte T129, 2013 frame, mongrel Revelations, Giant dropper, Stans S1 wheelset. 12, Magura Trail Sport brakes, 1x11. 12.8Kg
  • shindigshindig Posts: 173
    The easier way to overcome new pad not going in is to remove the wheel, remove the reservoir cap and then using a wide flat screwdriver, push the pistons into the calliper (keep the old pads in just now), put the reservoir cap back on. Then change pads, put the wheel back in. Then centre the calliper and pistons as shown on the video below.

    http://www.youtube.com/watch?v=akIWGqEE0PY
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