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  1. #1
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    Hayes Nine Bleed Pressure Issue

    Hey Everyone, I recently put together a bike using Hayes 9 hydraulic brakes which my friend gave to me. When he had the brakes he crashed the bike hitting the protective cap on the front of the right (rear) brake on a rock which caused oxygen to enter and the brake to loose pressure. I had that brake bled but it may or may not have an issue... Whenever I press the lever it catches just fine but if I let off a bit (not all the way) and then press it down again the lever will go closer and closer to the handle bar until i have no pressure in the break. Same thing happens if I push the brake lever real slow. The mechanic who bled the break said that this happens with some of the newly bled breakes but I am sceptical about his response. I have no prior experience with hydraulic brakes and don't know if this is normal, and input or help on fixing this issue will be highly appreciated.

    P.S. the brakes are NOT leaking fluid and as long as i release the lever completely is breaks just fine next time i push it.

  2. #2
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    That's strange b/c unless you've fixed it, if air (which is only ~20% oxygen so if you said nitrogen, it would have been more accurate) can go in, fluid can come out. Now to try and be helpful, what you are describing sounds like a bad M/C piston. http://aebike.com/page.cfm?action=de...=30&SKU=BR4498
    Of course, I can't explain how that got killed in a crash - perhaps it was on it's way out.

  3. #3
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    I did some more research based on what you said and it sounds like you're correct. The air isn't getting into the fluid because the brake is not degrading in performance and no fluid is coming out so I don't exactly understand how the brake could do what it does, but there is nothing that else could be wrong, i.e. the spring, retaining ring and washer all seem to e doing their job.

    Thanks again

  4. #4
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    Quote Originally Posted by kdubovenko
    I did some more research based on what you said and it sounds like you're correct. The air isn't getting into the fluid because the brake is not degrading in performance and no fluid is coming out so I don't exactly understand how the brake could do what it does, but there is nothing that else could be wrong, i.e. the spring, retaining ring and washer all seem to e doing their job.

    Thanks again

    I smacked a tree with my brake lever once. Afterwards I could squeeze the brake and it would grab but would then just squeeze to the bar. I had to pump the brake keep it working.
    A tiny hole was in the rubber seal of the master cylinder. The extreme pressure of hitting the lever caused the hole. It sound like you should replace the master cylinder cart. and rebleed the brakes.

  5. #5
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    If my memory serve correct however, the HFX9's lever isn't like the HFX mag or my HFX comp. The HFX mag has an MC inside a rubber bladder. The HFX9's MC seems to be a part of the lever assembly itself so there's no cartridge. You can either replace the piston assembly or the whole lever.

  6. #6
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    Quote Originally Posted by vk45de
    If my memory serve correct however, the HFX9's lever isn't like the HFX mag or my HFX comp. The HFX mag has an MC inside a rubber bladder. The HFX9's MC seems to be a part of the lever assembly itself so there's no cartridge. You can either replace the piston assembly or the whole lever.
    Well for the sake of brevity, I refer to the whole assembly as the master cylinder. It cost like $30. I replaced it myself. It was very easy. Remove hose from lever. Remove lever blade from piston arm. Remove C-clip and the whole piston assembly pulls out. Put new assembly back in. Reassemble. You need a new compression ferrule/bushing as well when you reattach the hose. Rebleed, Done! 30mins tops!

    I still have the old assembly/cart and can post a pic if the OP wants.
    Here's what the rebuild kit looks like!

    Rebuild Instructions here:
    http://www.hayesdiscbrake.com/pdf/HF...68BEnglish.pdf
    Attached Images Attached Images

  7. #7
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    You mentioned M/C cartridge which I thought referred to bladder w/ basically everything except the blade and lever body which is expensive. AEbike (on the link I posted) has the piston for $11 but AEbike from my experience, takes while some time to get you your stuff.

  8. #8
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    thanks a bunch guys, so would I be able to get away with just replacing the piston or do i need to get the whole $30 assmebly?

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    thanks a bunch guys, so would I be able to get away with just replacing the piston or do i need to get the whole $30 assembly?

  10. #10
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    if your nosecone, and pushrod are fine, there's no need to get those.

  11. #11
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    Quote Originally Posted by kdubovenko
    thanks a bunch guys, so would I be able to get away with just replacing the piston or do i need to get the whole $30 assembly?
    Well it depends on how easy it is for you to get the parts. If your lbs stocks the parts just get what you need. There may be other issues to fix. For me it was just easier to order the whole assembly. LBS didn't have the part in stock.

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