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  1. #1
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    Do avid brakes breed air bubbles?

    So I had to bleed my brand new stock elixir r front brake after a day of use because it was mushy as hell. That was 3 months ago. I have a pretty thorough procedure to bleed the avids cause they seem to store air bubbles. I am fairly confident all air was out of the system. So after 3 months of heavy riding and pretty much the same treatment day in and out, the brake went mushy again and started to make some howling over the last few days. So I rebled them again today and a lot of air came out and the howling is gone.

    So no fluid leaks whatsoever and for the last 3 months the brake has been solid.
    Now all of a sudden I have a lot of air in the system. Something ain't right.
    Could air be seeping in from the lever bleed port but still keep fluid from leaking?

    Anybody else have air show up in their avid system out of nowhere?

  2. #2
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    Air is in the brake fluid before you even put it in the system. It's just like a can of soda. Three months seems like a reasonable amount of time to go between doing periodic maintenance on a bike that's ridden frequently.

  3. #3
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    Quote Originally Posted by RustyIron
    Air is in the brake fluid before you even put it in the system. It's just like a can of soda. Three months seems like a reasonable amount of time to go between doing periodic maintenance on a bike that's ridden frequently.
    Havn't heard of the brake fluid like soda theory I have run hyd. brakes for seasons in a row w/o doing a re-bleed. Bicycle brakes run a closed hydraulic system. Proper bleeding is a must.

  4. #4
    I should be studying...
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    Likewise, I run mineral oil brakes (shimano) and I have gone years without a rebleed. If had to rebleed my brakes every three months I would have gone to cables. While it's not an absurd idea that there are gases dissolved in brake fluid...I'm not sure how soluble gases are in DOT fluid (or for mineral for that matter) but my guess is that stuff is designed to not have those kinds of problems. Either you need to revisit your bleeding techniques, or you have a faulty seal somewhere in your system.
    Formerly known as iceaxe

  5. #5
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    My bleeding technique is very thorough and includes a few more steps than Avid's procedure. I also de-gas the brake fluid multiple times during the bleed process as well as before the bleed.
    One could reason that I didn't degas the fluid enough (not likely), but I have owned hayes mags and 9's for years and never degassed the DOT fluid. Never have they just gone to mush out of nowhere.

    Either air is somehow migrating in or there is a massive air trap in the system.

  6. #6
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    There's a reason that Avid specifically tells you to degas brake fluid before bleeding. If you pull a vacuum on the fluid, LOTS of air bubbles come out. The Hayes is not quite so sensitive to such things. But I'm sure that degassing the fluid before bleeding could improve the bleed on those brakes too.

    Either you are not getting all the air out, or you have a leak. Check the line for any bulges or kinks or leaks. Check around the pistons for wetness. Check between the caliper halves for weeping. Check the torque on the caliper bolts. Check to see it isn't leaking around the banjo or any of the fittings. I would take off the caliper and hang it below the lever. Tap and rotate the caliper while bleeding to free up any stubborn bubbles.

    I've gone a couple years without touching my Avid J7s when I wasn't riding that much. I commute everyday on my Elixir Rs. And I rode trails pretty frequently over the summer. I got them in May. Bled them when they were new. I have not had to touch them since.

  7. #7
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    I found degassing to be crucial, but long-lasting, on my Juicy 7s. One surprise was the first time I took the bike up to over 10,000' in elevation (coming from trails under 5,000'): total mush because the fluid outgassed more. Of course, I discovered this while descending a steep and had to figure out that pumping the brakes would work.

    Later, I did another bleed while at the base of the mountain, and just pulled the air bubbles that had collected in the resevoir. After that, perfection for another two years before I changed that fluid.

  8. #8
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    I find the whole de-gas to be a load of BS.Fill the bottom syringe,push it through the system,perfect bleed.The bleed on my old Juicy5s was still good after 18months.The bleed on my Ultimates is 5 months and perfect.Avid seem to complicate an uncomplicated procedure.
    RE the OP,you haven't accidentally pressed the lever with the bike upside down have you?Avid systems don't like it
    Sometimes if you pump the lever and tie it to the bar(zip-tie etc) overnight a squishy lever can come up good again

  9. #9
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    A troubling issue arose this past weekend during a race. I broke the chain a third of the way into the race, flipped bike upside down to repair the chain, got back on to pedal away and when i squeezed the front brake, the lever came all the way in and made contact with the grip. WTF??

    Ok, don't panic. Luckily these brakes have the pad contact adjusters. So i turned the red dial all the way out. Got it to where it was before but now it was fully maxed out.

    Anyone have similar issues with their Elixir CR's or know why this occurred?

    I can't image air entered the brake system. Heck i didn't even take the front wheel off. The bike is less than 2 months old.

  10. #10
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    There was air in the system before you started. By turning the bike upside down, you moved the bubble to a place where it could adversely affect the operation of the brakes.

    The "pad contact adjuster" is inappropriately named, and has nothing to do with the pads. The PCA affects how far the lever travels before the master cylinder starts pushing brake fluid down the line. It's like the "take-up" on a trigger on firearms.

    I think it'ss a gimmicky and dumb feature, and can't understand why anyone would want more lever travel prior to the pads touching the rotors. But that's not what you asked. To summarize: bleed the brakes.

  11. #11
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    My thought is to make sure you're using fresh/sealed fluid. Brake fluid absorbs what ambient air it can and will go bad if from an old or unsealed bottle, causing the absorbed air to come out of solution with temperature increases (or pressure decreases?-correct me). It's really wasteful but Ive found no other option but to use a new bottle of automotive fluid, hopefully you need to do the car too, the unused portion gets recycled.

  12. #12
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    Quote Originally Posted by RustyIron
    There was air in the system before you started. By turning the bike upside down, you moved the bubble to a place where it could adversely affect the operation of the brakes.
    Although I appreciate your advice, i don't agree with your statement. If there was air in the system before, then this would have been evident right away. As well, I've flipped the bike over many times prior to my chain breaking. Also, the location of air bubbles in a closed system (ie. vacuum) is irrelevant to correct functioning.

    I've bled many a brake on my motorcycles so i understand how the system works.

  13. #13
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    Quote Originally Posted by ibbo
    I find the whole de-gas to be a load of BS.Fill the bottom syringe,push it through the system,perfect bleed.The bleed on my old Juicy5s was still good after 18months.The bleed on my Ultimates is 5 months and perfect.Avid seem to complicate an uncomplicated procedure.
    RE the OP,you haven't accidentally pressed the lever with the bike upside down have you?Avid systems don't like it
    Sometimes if you pump the lever and tie it to the bar(zip-tie etc) overnight a squishy lever can come up good again
    Then there was air in the SEALED brake system, turning the bike upside down and pulling the brake lever does nothing bad unless there is AIR in the system. Been there, done that and re-bled with proper procedure.
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  14. #14
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    I don't remember ever having mushy brakes before, but recently when I was moving my bike vertically balanced on the back wheel, the brakes went soft. I've had the bike for three years and never bled it once so far. If there was trapped air after the bleed, I'm sure It would have worked its way out quickly, or at least in a few years. It was fine with zero maintenance and now all of a sudden there is air-- that's not a result of not degassing the fluid. I guess there must be a tiny leak somewhere letting air in or fluid out. It's plausible that there could be some kind of reservoir where air can collect and not interfere with brake operation, but when the bike is turned upside down that air moves to somewhere it shouldn't be. It would make sense to design the brakes this way so they are tolerant of less than perfect bleeds or slight leaks or whatever.

    When I bleed the brakes I plan on degassing the fluid with my ghetto vacuum pump. It's basically a 12V tire inflator with a hose fitting glued to the intake. I can get about 10 PSI vacuum below ambient pressure, which is probably better than what you can get using the syringes to degass as instructed by Avid.
    http://www.instructables.com/id/conv...ressor-into-a/

    I also made a ghetto vacuum gauge by gluing a regular pressure gauge inside a jar, with the intake open to the air and another fitting on the jar to attach a vacuum line.

    Degassing does have very real benefits in theory. I made the vacuum pump to degas epoxy, which is thick so tiny bubbles are often trapped in it and never rise to the surface (or at least not before the epoxy cures). Pulling a vacuum on it makes the bubbles expand so they are big enough to float to the top. I don't know whether or not this makes any significant difference with brake fluid since the bubbles are probably too small to have much effect, but it can't hurt.
    Matt

  15. #15
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    plain and simple; cr's (at least the early production runs) i believe just have crappy enough master cyclinder seals to let air in, even if fluid doesnt leak out. my original cr's had huge problems with air leaking in, and even fluid leaking out. Took 2 warranty replacements but now seems better. Still have to bleed lever every few months though, but its easy.

  16. #16
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    @m85476585, good idea I have a hand vacuum pump I may try....Avid's plunger bleeding setup is a pos imo....can't hardly pull any vacuum before the plungers leak air!?!?!!

    @dwyooaj, could be I've had issues with Juicy 3.5 where the master cylinder seals were jacked from the factory causing levers to stick and then seperate issue of the calipers not extending evenly....in other words one side does most of the moving and hence the work of squeezing the pads together and the LBS and I have both had them all apart several times.
    Fat, drunk, and stupid is no way to go through life son...

  17. #17
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    Quote Originally Posted by m85476585 View Post
    I don't remember ever having mushy brakes before, but recently when I was moving my bike vertically balanced on the back wheel, the brakes went soft. I've had the bike for three years and never bled it once so far. If there was trapped air after the bleed, I'm sure It would have worked its way out quickly, or at least in a few years. It was fine with zero maintenance and now all of a sudden there is air-- that's not a result of not degassing the fluid. I guess there must be a tiny leak somewhere letting air in or fluid out. It's plausible that there could be some kind of reservoir where air can collect and not interfere with brake operation, but when the bike is turned upside down that air moves to somewhere it shouldn't be. It would make sense to design the brakes this way so they are tolerant of less than perfect bleeds or slight leaks or whatever.

    When I bleed the brakes I plan on degassing the fluid with my ghetto vacuum pump. It's basically a 12V tire inflator with a hose fitting glued to the intake. I can get about 10 PSI vacuum below ambient pressure, which is probably better than what you can get using the syringes to degass as instructed by Avid.


    I also made a ghetto vacuum gauge by gluing a regular pressure gauge inside a jar, with the intake open to the air and another fitting on the jar to attach a vacuum line.

    Degassing does have very real benefits in theory. I made the vacuum pump to degas epoxy, which is thick so tiny bubbles are often trapped in it and never rise to the surface (or at least not before the epoxy cures). Pulling a vacuum on it makes the bubbles expand so they are big enough to float to the top. I don't know whether or not this makes any significant difference with brake fluid since the bubbles are probably too small to have much effect, but it can't hurt.

    Matt - Did you have any luck degassing the DOT fluid prior to bleeding? Have you found out how fast previously degassed fluids will re-absorb gasses?

    I'm wondering because I have access to a pretty strong vacuum at work Could I degas and but in a jar to do a real proper bleed job once I return home?


    Thanks,
    Skymeat

  18. #18
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    I don't remember if I used the vacuum pump, it's been over a year now!

    I know that I'm not 100% satisfied with the bleed. The brakes are still a little soft, but I blame the fact that it was my first time bleeding brakes, and I'm not very good at it yet. I don't ride that bike much most of the time, though, so I haven't done anything about it.

    I don't think degassed fluid will reabsorb gas any more than normal fluid, but I would be worried that in transporting the fluid from work to home you would introduce more bubbles.

    If you are able to vacuum the fluid keep the jar sealed under vacuum you would probably get very good results. A strong vacuum should also be good to eliminate any moisture that might have gotten into the fluid.
    Matt

  19. #19
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    fliping bike over.

    http://techdocs.shimano.com/media/te...9830607840.pdf note the blue Warning paragraphs.Shimano clearly says to avoid it in their setup instructions.can't be any better with avids.the remedy to fix a mushy lever is to remove the master cover & gently pull the. Lever till no more air bubbles appear.worked well for me.
    Last edited by 02_NRS; 03-04-2012 at 07:59 AM. Reason: forgot.

  20. #20
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    Quote Originally Posted by '02 NRS View Post
    Shimano clearly says to avoid it in their setup instructions.can't be any better with avids.the remedy to fix a mushy lever is to remove the master cover & gently pull the. Lever till no more air bubbles appear.worked well for me.
    its a bit more complicated than that, the pads should be out and bleed block put in before doing this, otherwise you might overfill the system. also, dont forget to top off the reservoir after all the air bubbles come out (shimano). For elixirs, tehres no reservoir cover, you have to do this with the syringe installed to suck the bubbles out as they are released by rapidly pulling and releasing the lever.
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  21. #21
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    Quote Originally Posted by m85476585 View Post
    I don't remember if I used the vacuum pump, it's been over a year now!

    I know that I'm not 100% satisfied with the bleed. The brakes are still a little soft, but I blame the fact that it was my first time bleeding brakes, and I'm not very good at it yet. I don't ride that bike much most of the time, though, so I haven't done anything about it.

    I don't think degassed fluid will reabsorb gas any more than normal fluid, but I would be worried that in transporting the fluid from work to home you would introduce more bubbles.

    If you are able to vacuum the fluid keep the jar sealed under vacuum you would probably get very good results. A strong vacuum should also be good to eliminate any moisture that might have gotten into the fluid.
    Bold by me.

    It depends. If you take a fluid that has been degassed and expose it to atmospheric pressure in the presence of air then it will reabsorb air till it reaches equilibrium. That's why it is difficult to keep a bottle of pre-degassed fluid around for bleeding. Just easier to degas the 5-8 mL needed for the bleed just prior to when you need it.

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