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Formula Oro K24 bleeding(?) problems

blazingmongablazingmonga Posts: 97
edited November 2011 in MTB workshop & tech
Hi guys,

I need a bit of help to sort my K24s out, as I am really struggling to troubleshoot what the source of the problem is and I'm hoping somebody can shed some light on the matter.

The problem started was when I started to lose feeling in my rear brake, when they would start firm but seem to lose pressure after repeated lever pulls. I figured that they at least needed a bleed so that was the first thing I did, however I then struggled to achieve a good bleed and only managed to make things worse. I've replaced the master cylinder seals and the reservoir too, as they seemed a bit worn.

I have found it impossible to bleed them successfully as (following the proper method) when I go to bleed the calliper (with the brake lever fixed/master cylinder closed) the syringe seems to fill with air endlessly. I can only assume that there is a leak somewhere near and that air is being pulled in from outside rather than from the fluid.

If I force fluid into the calliper I can't see any obvious massive leak. 2 areas that seem to look wet with fluid are the edges of the pistons and the banjo bolt. I've replaced the piston seals - but not the pistons themselves.

Any ideas where the leak could be coming from? Do the pistons wear down, as well as the seals? Do banjo fittings fail? The next things I could replace is the pistons and then the copper washers/banjo bolt. I'm just guessing though. I dont want to keep replacing things for no reason as its getting expensive!

Any help most appreciated...

David

Posts

  • nicklousenicklouse Posts: 81,520 Lives Here
    piston do wear but will take many many years.

    bleed as best you can lock it all up. clean with a cleaner and leave pressurised over night and see where the damp patches are.
    "Do not follow where the path may lead, Go instead where there is no path, and Leave a Trail."
    Parktools :?:SheldonBrown
  • Thanks Nick!

    I tried what you suggested and found the area around the banjo bolt to be moist. I looked into it further and replaced the o-ring from between the caliper halves. I also replaced the copper washers with some stainless steel ones as one seemed to have a nick in it.

    Anyway, long story short, I seem to have managed a semi-decent bleed and there seems to be pressure in the system.

    Fingers crossed I have found the problem. Thanks for the tip, it may just have finally sorted it.

    -David
  • nicklousenicklouse Posts: 81,520 Lives Here
    copper for steel..... not good. the copper can deform to take any "issues" up steel does not.

    see how it goes.
    "Do not follow where the path may lead, Go instead where there is no path, and Leave a Trail."
    Parktools :?:SheldonBrown
  • 386ka386ka Posts: 479
    nicklouse wrote:
    copper for steel..... not good.

    This. ^

    Copper deforms and acts like a gasket. After refitting, you should use new copper washer, just like you do with engine head gasket.

    Steel is much more harder, and will not deform, and may be a cause for a leak. Anyway, see how it holds up, and replace with new copper washer if it leaks.
    A much loved, Giant Trance X3 2010
  • Eep, I suspected that may be why the washers were copper. It doesn't seem to be leaking at the moment. Have bought an assortment of copper washers today and I will replace asap.

    Seems I am finally getting to the bottom of all this anyway!
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