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  1. #1
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    Black speck's in brake fluid?

    I have Juicy 7's, and I'm having trouble bleeding the brakes. The rear in particular, although both lines have some amount of residual air in them. I've bled plenty of brakes before (non-mountain bike, though), but with the Juicy's I keep getting large air bubbles sucked into the caliper syringe. I'm following the instructions exactly and it seems I'm sucking air in somewhere. I haven't seen any leaking during normal use, including the caliper and brake resevoir.

    The other thing that makes me suspect a seal breakdown is that there are little black speck's floating in the brake fluid. Is this normal for the avids? I've been using DOT 4. I've read some people have had problems with the resevoir diaphram leaking, does this sound like my problem?

    I really like the performance of these brakes, and I think I finally fixed the obnoxious squeal, but now this is getting old. I'm either going to replace all the seals in the caliper/master/resevoir or pick up some magura's instead.

    So what's up with the black stuff in the fluid?

  2. #2
    Meh.
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    The first time I bled my Avids, I had little black specs. They were gone after that. My Hayes would occasionally have specs in the brake fluid.

    Are you isolating the MC when you bleed it (having the lever depressed)? I just kind of get it "good enough" then if there's any air towards the top/front of the line, it'll get pushed out when I force fluid back through the system. I personally find it much easier to bleed with larger syringes.

  3. #3
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    FWIW, I've bled my brakes three times (none of which ever eliminated all the air), and each time there was more black stuff floating around in the fluid. I have run enough fluid through the system that I'm sure I've flushed it out at least 5 times. Funny thing is the clutch fluid on my Ducati turns black after a few weeks but it always works just fine.

    Yes, I've been isolating the MC when bleeding the caliper. My concern is the large air bubles I suck into the syringe when bleeding. They have to come from either air in the existing lines (I don't think this is the case) or from a seal that leaks under a vacuum when bleeding.

    I should try some bigger syringes, like you suggest. It is possible that this is my problem and that the black speck's are just a distraction. If you have a fair amount of air in the lines the avid syringes lose their effectiveness after they suck up some air since you can no longer pull a strong vacuum. I have some 60 mL sryinges that I should try.

  4. #4
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    Update

    OK, I re-bled the brakes tonight with a larger (60 mL) syringe. No improvement, still air in the lines.

    So when I bleed the caliper, I get large bubbles sucked up into the syringe. The air is not coming in by burping past the top syringe o-ring, since it can be seen traveling in the plastic tube connected to the bleeder. I don't think this much air was trapped in the lines before I started the bleed, because the lever would've went right to the bars. I think there are two possibilities:

    1. There's a bad seal/o-ring somewhere and when I pull a vacuum air is drawn into the sytem past this seal.

    2. I'm pulling too strong of a vacuum with the syringe, and this is causing air to leak past a seal or maybe even the threads of the bleeder/syringe fittings. Sucking in air this way would obviously defeat the purpose of bleeding the lines. Has anyone actually run into this with the Juicy's or am I thinking too much?

  5. #5
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    1) are you sure you are not sucking air at the point of attachment of the clear bleeding tubing?

    2) why don't you just take the pads out and pop the pistons out and inspect the O-rings. you might be able to see clear and evident damage. they can come defective if it becomes pinched during assembly at the factory. your O-ring could have been bad to begin with and now it's really bad.



    edit:

    black specs most likely from "abrasion" of piston against O-ring. little rubber flakes. well, i shouldn't say most likely....but could be.

    edit II:

    after reviewing the service manual, don't forget about the O-ring between the caliper bodies at the banjo bolt connection. i have no idea why it would be faulty...but you never know!

    how much use have these brakes seen?
    Last edited by mx_599; 02-20-2007 at 11:25 AM.

  6. #6
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    came across the same deal. you can pull on the syringe plunger for hours and still see air bubbles coming up the clear tube.
    i finally gave up they worked when i was done. besides the front does most of the stopping

  7. #7
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    Quote Originally Posted by mx_599
    1) are you sure you are not sucking air at the point of attachment of the clear bleeding tubing?
    Pretty sure. I can see the air bubble entering the clear tubing from the caliper. Plus I safety wired the clear tubing to the adapters to make sure they were tight.

    Quote Originally Posted by mx_599
    2) why don't you just take the pads out and pop the pistons out and inspect the O-rings. you might be able to see clear and evident damage. they can come defective if it becomes pinched during assembly at the factory. your O-ring could have been bad to begin with and now it's really bad.
    I just ordered new seal kits for the levers and calipers. I'd rather have all the replacement parts on hand when I tear it down, so my bike isn't out of commission while I wait for shipping.


    Quote Originally Posted by mx_599
    black specs most likely from "abrasion" of piston against O-ring. little rubber flakes. well, i shouldn't say most likely....but could be.
    I will post an update if I find anything of interest.

    Quote Originally Posted by mx_599
    how much use have these brakes seen?
    I bought them new about 3-4 months ago. Two rides per week on average.

  8. #8
    Meh.
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    You could just be one of the unlucky ones. Warranty issue? You'll have to take it to the shop to have them warranty it though. SRAM is usually pretty quick with turnaround, it's the shop that you have to wait on. SRAM ships out a new brakeset and an RA number. So really, you should get the new brakes before you have to send the old ones back.

  9. #9
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    Quote Originally Posted by XSL_WiLL
    You could just be one of the unlucky ones. Warranty issue? You'll have to take it to the shop to have them warranty it though. SRAM is usually pretty quick with turnaround, it's the shop that you have to wait on. SRAM ships out a new brakeset and an RA number. So really, you should get the new brakes before you have to send the old ones back.
    Could be covered under warranty, but I'd rather do the work myself and eat the cost. That way I know the work was done right, plus I don't like anyone else working on my stuff.

    I gotta say, from my perspective, not being able to deal directly with SRAM sucks.

    Thanks for all the help.

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