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Just lost some fluid from my front hydraulic brake

DitlanDitlan Posts: 19
edited November 2018 in MTB workshop & tech
Hello,

So first time using a bike in a long while, and first time with hydraulic brakes.

The front brake didn't have much stopping power and was pretty spongy, I was giving it a clean and having a look at it and when I had taken the pads out I noticed one of the 'barrels' (right word?) was pushing out properly and the other was barely moving.

Intrigued, I gave the brake a squeeze and out popped one of the barrels along with a load of fluid.

So...

1. Can I fix this? - should I just take it to a shop?
2. How do I get the other barrel to move if I manage to fix the above?

Thanks for any advice!

Posts

  • The RookieThe Rookie Posts: 27,748
    Its a piston.

    And the make and model of the brake is?

    You can probably put the piston back in and then will need the system bled to remove the air and refill with fluid.

    Its perfectly normal for one piston to move and not the other, one will always have slightly less friction, fact of life.
  • DitlanDitlan Posts: 19
    I see, its a Tektro Auriga pro.

    I can see kits online for about £24 - seems easy enough to bleed/refill the system - I like to do these things myself as I'll learn for future, but if its more complex that it looks I can have it done by a shop.
  • DitlanDitlan Posts: 19
    I put it straight back in - went in very easily in fact.

    The other piston was not moving at all to my eye, but would I be right to guess that with no push back from hitting the discs the one that moves more easily would have been the only one to move in any case?
  • 02GF7402GF74 Posts: 1,294
    Correctly functioning brakes both pistons should move, sounds like one of them is seized.

    Put cable tie around the moving one and pop the seized one out by pressing the brake lever.
    . Clean the piston and seal before refitting it, lubricating the sides of the piston with brake fluid.
  • DitlanDitlan Posts: 19
    Thanks, I have now done this with both pistons and I have a draining/filling kit on the way so hopefully have it all sorted in the next day or two.
  • The RookieThe Rookie Posts: 27,748
    Sorry he’s talking rot, it’s perfectly normal with no external resistance such as the pad hitting the disc for only one to move, the chances of them having identical friction is just about zero and once a piston starts moving it’s has les friction than the static one. It’s rare to see both move with no disc in there.
  • 02GF7402GF74 Posts: 1,294
    Rot or not, just now I dropped the front wheel from my Cannondale, with Xt disc brakes, which is the daily commute bike so sees more use/wear n tear, than any other bike, gently squeezed the lever and BOTH PISTONS started to move at the same time. They appeared to move same amount but I wasn't going to spend any more time on this to measure accurately.

    So despite the plausible explanations of why this cannot happen, I can see that it does. OK, this is a small sample but whenever I've had to centre a calliper, I do not recall seeing only one piston moving, but admittedly it was not something I was looking for.

    What the Op chooses to believe is neither here nor there, I see what I see and stick behind what I posted above.
  • billycoolbillycool Posts: 833
    Both of my pistons move (SLX and XT) - one seems to move more than the other.

    Does that make me right or wrong?

    In the majority or minority?

    I'm so confused......
    "Ride, crash, replace"
  • kajjalkajjal Posts: 3,380
    billycool wrote:
    Both of my pistons move (SLX and XT) - one seems to move more than the other.

    Does that make me right or wrong?

    In the majority or minority?

    I'm so confused......

    In reality the pistons rarely move exactly the same but the difference is rarely enough to make setting the brakes up properly an issue. The rear calliper on my road bike has one piston moving more than the other so after all the normal adjustments to get it working normally I just adjusted it by eye for the best result. There is no rubbing and the braking is fine.
  • veronese68veronese68 Posts: 23,738 Lives Here
    billycool wrote:
    Both of my pistons move (SLX and XT) - one seems to move more than the other.
    Does that make me right or wrong?
    In the majority or minority?
    I'm so confused......
    Quite normal I'm afraid, sorry if that doesn't make you feel special. :wink:
    As Rookie says the friction is rarely the same so one will often move more than the other, or only one will move. But if you hold the moving one in the other should move. Only then would you be able to tell if one is seized, with nothing pushing back uneven movement means nothing. When the pads and disc are in there is very little movement and the clamping pressures will be very close to being even, unless one piston really has seized.
    The usual rule of not messing with them if they work applies. With regard to the OP the brake shouldn't feel spongy, but if a new disc brake set up isn't very strong it may just need bedding in.
  • DitlanDitlan Posts: 19
    Well, I refilled the brakes with a kit from Amazon - got mineral oil everywhere but managed to get them sorted. They are no better than they were when I started however and I still think the front wheel doesn't have enough bite.

    It might be the pads, but the bike is in pretty dire need of a good service anyway (belongs to a friend) so I might just get it fixed up at a shop to thank him for the lend.

    edit: oh and although I did take the pistons out and give them a wipe, however one still moves more than the other, if it adds anything to the above :lol:
  • veronese68veronese68 Posts: 23,738 Lives Here
    Pads could be contaminated. New pads, clean the discs with IPA (isopropyl alcohol, not beer) before fitting the pads. You may have to bed the pads in by braking hard from a normal speed but not quite to a stop repeatedly. After a few goes the braking should improve. If the brakes still feel spongy you may need to have another go at bleeding them. Once you've got them sorted keep all chemicals away from them, even cleaning ones.
  • Hi All

    I need to bleed my Tektro Auriga Pro brakes, but I'm worried since the valve on the tank is not on the cap but on the side of the tank. I thought it should be in the highest point of the circuit. Should I disassemble the block from the handlebar and hold it on its side?

    Thanks!
  • Vino'sGhostVino'sGhost Posts: 4,129
    gianniTS wrote:
    Hi All

    I need to bleed my Tektro Auriga Pro brakes, but I'm worried since the valve on the tank is not on the cap but on the side of the tank. I thought it should be in the highest point of the circuit. Should I disassemble the block from the handlebar and hold it on its side?

    Thanks!

    heres the video guide https://www.youtube.com/watch?v=cS0pBCBT65g
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