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  1. #1
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    Avid owners-sticky pistons are the root cause of the turkey warble.

    I think I solved the turkey warble problem--A STICKY PISTON.

    This morning I removed the pads in my rear caliper and squeezed the lever to moved the pistons out so I could clean them. The outside piston moved out with each stroke while the inside piston remained in its fully retracted position, which was flush with the top of its cylinder. I pushed the outside piston back into its cylinder and repeated this procedure another three times without any movement from the inside piston. I also noticed the outside piston was very difficult to push back into its cylinder. I then held the outside piston in its retracted position with the flat blade of a screwdriver and pulled the lever. On the second stroke the inside piston started to move and on the third stroke it moved out the same distance as the outside piston did. Next I released the outside piston and both pistons moved out equal distance together. I pushed both pistons back again, which was very easy to do this time, and pushed them out again with the lever until they were about 3mm apart. Cleaned them with a swab dipped in isopropyl alcohol and pushed them back in for the last time. Installed the pads, aligned the caliper, torqued the CPS mounting bolts to 75 inch pounds and when for a 14 mile ride. Guess what--not turkey warble sound or vibration for the first time in over a year.

    Throughout this last year, I have tried all of the anecdotes that are described in the previous 300 plus posts to fix my 2007 J5 rear brake, which sounded like a turkey in heat and vibrated the rear end of my bike every time I squeezed the lever. Here are all the things I tried before I stumbled onto this sticky piston: 1) Aligned the caliper, cleaned and sanded the pads and rotor countless times, 2) new organic pads, 3) new semi-metallic pads, 4) swapped out the 185mm G2 rotor with a new 185mm G2 rotor under warranty, 5) new 160mm G2 rotor along with a new extruded adapter, which significantly reduced the vibration, 6) tried an old 160mm G1 rotor from my BB5s, 7) tried an old 160mm round-a-gone rotor off of a set of 05 J5s installed on my wifeís bike, 8) replaced the CPS washers and 9) bled the brakes twice.

    The cause of the turkey warble is obvious to me now, the pad with the sticky piston just grazed up against the rotor, which had zero clamping effect whatsoever. The opposite pad, with the active piston, was pushing up against the rotor and distorting it and the uneven friction was causing the system to vibrate and resonate. With both pad equally clamping down on the rotor any vibration caused by friction is dampened as the clamping force is increased. Case and point, the turkey warble could probable be reproduced with a large gap behind the static pad in a BB5 or BB7 caliper.

  2. #2
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    Isopropyl Alcohol is not good for cleaning caliper interiors/pistons as it can dry out and harden the seals, leading to either stuck pistons or to fluid being able to pass the seal. Use brake fluid (DOT or mineral, as appropriate) or a silicone spray lubricant instead.

    I pointed a fair while ago towards the CPS system as the most likely cause of the multitude of unwanted noises coming from Avid brakes, mostly because it does not consider the exact problem you've uncovered. It's not unusual for a new brake to have one piston moving at a different speed to the other, or even not at all, and the CPS method will hide this from all but the most attentive mechanic, leaving the user with a problematic brake.

    With the exception of using IsA to clean/lubricate the pistons, it's good advice you're offereing and hopefully it will at least get people checking their brake installation for correct alignment.
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  3. #3
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    It is also fixed with a non avid rotor...Seems like you didnt try that. This was mensioned over in the Cannondale forums yesterday, someone called up SRAM.

  4. #4
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    Quote Originally Posted by amillmtb
    It is also fixed with a non avid rotor...Seems like you didnt try that. This was mensioned over in the Cannondale forums yesterday, someone called up SRAM.
    Out of curiosity I went to the Cdale forum; you're paraphrasing Cyclemendonsmith, he said he called SRAM in one post and got a "really we don't know" answer about the noise issue. In another post he was recommending that perhaps a Shimano rotor might solve the problem, but he didn't attribute that to SRAM. I've been running mechanical Avid BBDB/BB7 brakes forever now, the only noise problem I've had is with the roundagon rotors, the clean sweeps have been fine.
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  5. #5
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    Quote Originally Posted by Bikinfoolferlife
    Out of curiosity I went to the Cdale forum; you're paraphrasing Cyclemendonsmith, he said he called SRAM in one post and got a "really we don't know" answer about the noise issue. In another post he was recommending that perhaps a Shimano rotor might solve the problem, but he didn't attribute that to SRAM. I've been running mechanical Avid BBDB/BB7 brakes forever now, the only noise problem I've had is with the roundagon rotors, the clean sweeps have been fine.
    Well, you wouldnt have the turkey gobble if you have bb7/bbdb's, its an Avid hydraulic brake thing. A sticky piston could fix it, but I think this was figured out a while ago..there is an "official turkey gobble thread."

    Here it is.. you can leaf through its nearly 500 posts
    The Juicy brake turkey warble/vibration MEGA THREAD

  6. #6
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    Well after my ride (without the dreaded turkey) I mounted my bike in a stand, removed the rear wheel and rear pads to check the inside piston one more time. And unfortunately, the inside piston barely moved compared to the outside piston. So I figure that there is either an obstruction in one of the caliperís hydraulic ports or there is an air bubble behind the inside piston. I might need to remove the entire brake from the frame and ďbenchĒ bleed it because air bubbles may be getting trapped in the line where it bends down from the caliper (which is mounted to the seat stay) and ties into the lower chain stay. The hydraulic line continues from the chain stay and up the main tube to the MC/lever. I wonder if the majority of the riders that are experiencing the turkey warble problem with their rear brake have their line routed like mine.

    A side note; I do note believe the Avid rotors (G1, G2 or round-a-gone) are responsible for the turkey vibration because the my 04 BB5ís with G1 rotor and my wifeís 05 J5ís with round-a-gone rotors never warbled in over four years of riding. However these older Avid rotors did do the turkey thing when I installed on my rear wheel of my bike with the 07 J5ís.

  7. #7
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    Quote Originally Posted by bwalton
    Well after my ride (without the dreaded turkey) I mounted my bike in a stand, removed the rear wheel and rear pads to check the inside piston one more time. And unfortunately, the inside piston barely moved compared to the outside piston. So I figure that there is either an obstruction in one of the caliperís hydraulic ports or there is an air bubble behind the inside piston.

    not necessarily, in a self balancing twin slave system ( like the juicys ) if one piston is suffering higher seal drag, the fluid will take the path of least resistance and move the other one, until it meets resistance high enough to overcome the seal drag of the stuck piston.

    to test it use a lever against the mobile piston and apply the lever. it may move the stuck piston, or it could be seized in the bore ( overhaul time )

    hydraulically speaking, the internal ports in a juicy caliper are quite large so a blockage strong enough to limit or stop a piston moving is unlikely ( but maybe not impossible )

    an air bubble behind on piston might produce the stuck piston effect on the workbench with the wheel out, but is more likely to make the brake spongy and weak, as air in any part of the high pressure circuit would.

  8. #8
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    vs shimano

    Funny, the knock on shimano has been their sticky pistons, but if you look at the reviews on mtbr, there seem to be at least (if not more) complaints about "brake rub" and the warble with avids. So much for the more reliable alternative.

  9. #9
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    The inside piston will move out normally if I hold the outside piston in place with a screw driver. After the first lever stroke, I can release the outside piston and then both pistons move out normally (equal distance) with each lever stroke. The inside piston seems to stick in the bottom of its cylinder only. There must be a gouge, a pit or a high spot in the bottom of the cylinder, which the pistonís seal in hanging up on. This irregular surface can only be attributed to poor machining-quality control. In the automotive world small irregularities in the steel brake cylinders can be reduced to reasonable tolerance by honing. Iím not sure if a small aluminum caliper bore can be honed. So unfortunately my rear caliper may be toast if the bore can not be brought back to tolerance. Too bad so many American companies choose to spend as little as possible in manufacturing their products. In the Turkey Warble tread, I remember reading that Avid had a bad batch of brakes-I wonder if my rear brake is one of them.

    So, what brake company builds the most durable disc brakes and provides the most comprehensive support for their products? Shimano or Hayes?

  10. #10
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    "So, what brake company builds the most durable disc brakes and provides the most comprehensive support for their products? Shimano or Hayes?"

    Hope?
    Last edited by SteveUK; 12-09-2008 at 09:36 AM.
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  11. #11
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    Take a look at Magura as well. The marta's are pretty top notch, and the 09's are supposed to have solved the reach / lever problems of the past martas. I think they redesigned the the shape of the lever, not sure.

    I have Juicy sevens. I didn't have turkey warble, but my rear brake was stiff / too firm, and had severe brake rub. I had sticky pistons on the rear as well. The inside piston was the culprit. After removing the pads, I used a silicon lube and worked the pistons in and out over and over until the movement was equal from both pistons. Haven't had any issues since.

  12. #12
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    Quote Originally Posted by jmb123

    I have Juicy sevens. I didn't have turkey warble, but my rear brake was stiff / too firm, and had severe brake rub. I had sticky pistons on the rear as well. The inside piston was the culprit. After removing the pads, I used a silicon lube and worked the pistons in and out over and over until the movement was equal from both pistons. Haven't had any issues since.
    This is the best bet on my XTR's as well. I was following all the online wisdom about cleaning and lubing and working the pistons in and out, but it took me a while (too long) to figure out that that can involve LOTS of iterations, and it still requires looking at the action on each piston and keeping at it until things are working well and the action is balanced (PITA).

    Also, SteveUK good interjection on the alcohol. I had been using it on a q-tip to clean the extended piston and letting the piston dry, then lubing it before working it back in (so I wasn't working the stuff into the seals, but the outside of the seals did get wiped with it). But now I'm wondering about using it at all...

  13. #13
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    jbm123, did you ever recheck your J7's inside piston after you lubed it with silicone? Pad drag has also plagued my rear J5 brake as well. I wonder if Avid has improved their piston and MC seals rubber compound in 2008 when they started filling their J5ís and J7ís with DOT 5 brake fluid. I know this is a rhetorical question but why does Avid use such cheap quality rubber in their hydraulic circuits? These rubber seals should last for years and their failure rate should be almost zero like the automotive and motorcycle-recreational vehicle industry.

  14. #14
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    Quote Originally Posted by SteveUK
    "So, what brake company builds the most durable disc brakes and provides the most comprehensive support for their products? Shimano or Hayes?"

    Hope?
    I'm thinking of picking up some hope minis,are they really a level up in quality when compared to avids and hayes

  15. #15
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    "I'm thinking of picking up some hope minis,are they really a level up in quality when compared to avids and hayes?"

    In overall quality (build/materials), I don't believe that any manufacturer comes close to Hope, especially now that they have redesigned the lever blade pivot assembly to utilise cartridge bearings rather than nylon bushings. I would consider Hope and Magura to be at the very front where build quality is concerned. Formula really should be in there, too, but there's something about their levers which just doesn't feel right, kind of flexy.

    Check out the pictures that Thomas posted of the new Tech lever and M4 caliper. That's the kind of quality you'll get from Hope and it lends itself to a very nice feeling brake. The original (black) Mini lever could feel a little flexy in more aggressive braking, something which was addressed with the '07 Mini Moto lever. That said, for typical XC style riding, the original lever is still very good.

    Hope try to cater for quite specific groups, rather than have one, do-it-all brake (although one could point to the Mono M4 for that title), so if you're doing faster AM type riding or are a heavier rider, the M4 may well be more appropriate than the Mini, at least for a front brake.
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  16. #16
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    Quote Originally Posted by bwalton
    I think I solved the turkey warble problem--A STICKY PISTON. .
    Nope, you solved your turkey warble problem. It's a resonance issue, and it's not just sticky pistons, or rotors, or pads, or hubs, it's the entire system allowing a vibration to propagate. The root cause being a fairly poor disc brake design IMO. I solved mine (with codes) by installing a marzocchi 888 over the fork I had on there. Does that mean everyone needs an 888? Nope. Pistons are ALWAYS going to move at different rates in a system such as hydro brakes, untill the pressure equalizes. Sticky pistons should only be causing problems if they are causing excessive drag. Avid stuff has never impressed me in terms of quality, but they've always seemed to be able to use extremely "grippy" pads for all of their brakes, giving good stopping power and modulation. While they tend to excel in this one area, the quality and other function aspects have not been consistant in my experience.
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  17. #17
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    I ran the same set of 05 J5's on two bikes without experiencing the dreaded turkey gobble/warble for over 3 years. Unfortunately, I have not had the same luck with the rear 07 J5, which came on my 07 Stumpy. So at least in my situation, I narrowed the problem down to the rear caliper with a sticky inside piston because the older 05 J5 round-a-gone rotor did not solve the issue when used it with the 07 J5.

    So the rear inside cylinder in my rear 07 J5 caliper most likely has an oxidation pit or crown on the lower wall, which the pistonís seal is hanging up on. This may have been caused by contaminated DOT brake fluid at the factory, moisture introduced into MC vent during the boat ride to the states, lack of silicone grease in the cylinder when it was assembled or a very long shelf life. I do not think the cylinder-bore can be honed out because the aluminum is way too soft so my only alternative is try the silicone spray or replace the brake.

    If I were to replace the brake I would like to run very durable disc brakes that are free of headaches for many years of riding. The older Shimano brakes seem to get better reviews overall, so I was wondering if newer XTís M775, which are manufactured by Magura, would be a good trouble free brake. Otherwise it seems like Avid mechanical BB7 disc brakes would be the best alternative until the quality of the hydraulic brakes are substantially improved over the next few years. Like the DOT 5 brake fluid, the mineral oil used in Magura and Shimano brakes is thicker than DOT 4 and is a little more resistant to absorbing moisture. Also I should avoid buying pre-bled brakes if I go with hydraulics again.

  18. #18
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    Quote Originally Posted by bwalton

    If I were to replace the brake I would like to run very durable disc brakes that are free of headaches for many years of riding. The older Shimano brakes seem to get better reviews overall, so I was wondering if newer XT’s M775, which are manufactured by Magura, would be a good trouble free brake. Otherwise it seems like Avid mechanical BB7 disc brakes would be the best alternative until the quality of the hydraulic brakes are substantially improved over the next few years. Like the DOT 5 brake fluid, the mineral oil used in Magura and Shimano brakes is thicker than DOT 4 and is a little more resistant to absorbing moisture. Also I should avoid buying pre-bled brakes if I go with hydraulics again.
    I've never felt that the avids were very quality brakes, my BB7 pad adjusters tended to back out on descents from lots of vibration (scary!), the adjuster knobs flew off never to be found again, and they tended to overheat pretty easy, eventually the caliper developed some play and it just seemed that they generally seemed to fall-apart in the 2nd season of hard use. BB7s have their place, but they just weren't anywhere near the level that I'd come to expect from other brake companies.

    I'd go shimano for a fool-proof setup, you can order the rotors seperate to get the non-centerlock versions. They had some initial problems with the XTR brakes, but otherwise they seem solid (I have the LX right now). They come with bleed kits and everything, so that is nice.

    I had maguras back in the day, there was always some little leak somewhere that allowed air into the system, my buddy bought new maggies and they kind of "fell apart". I'm sure they've since cleaned up their act, but hayes and avid both gave me some trouble as well over the years, hayes with the two-peice-caliper seal eventually giving out and avid with the before mentioned BB7 problems and the crazy vibration problem that the hydro avids are known for.

    On the other hand, hope has been rock solid for me, they seem to be much higher quality and they simply always "work". I wouldn't heasitate to buy them (if I had the $$) or the shimano brakes again. I started back in 1999 with hope DH4s, had those for about 4 years and then bought mono M4s a few years ago, and both have just been solid. I don't want to make this sound like you should buy hope, but my point is that with certain companies I've had consistant sucess, rather than failure after failure. I got avid codes recently because they were cheap, but that's kind of the point, they just recently started making one-peice calipers as companies ilke hope have been doing for years, and while shimano is kind of new in the game, they usually don't enter any market without extensive testing. Sometimes they miss they mark, but I have a lot more confidence in their R&D and testing compared to hayes or avid.
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  19. #19
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    Well, a J5 caliper rebuild kit goes for $35.00, which may or may not fix the problem depending on how pitted the cylinder walls are. Plus a $5.00 bottle of DOT 5.1 brake fluid will hopefully bring the rear brake back to life for around $40.00 and a few hours of labor assuming I have all the necessary tools.

    My second and least expensive option would be to install a set of 04 BB5's on my bike, which will cost about $10.00 for brake cables and housing and about an hours worth of labor.

    Did Avid improve their 08 line of BB7's or are they exactly the same as my older 04 BB5's?

    The third and most expensive option would be to purchase a set of Shimano XT M775 brakes and two 160mm XT 6-bolt rotors for around $350.00, which will take less then an hour to install if my rear ISO frame tabs are true. Another unexpected expense may be a bleed kit if the brakes are spongy. I also remember someone posting that the stock M775 pads need to be replaced with organics pads in order to reduce the noise and get modulation from the brakes. So the total potential price for this option is more like $400.00.

    Side questions:
    1) What is the boiling point of the Shimano mineral oil?
    2) Can you store your bike upside-down with M775 brakes? Fox forkís requires that their forks be stored upside-down in order to keep the bushings and seals lubricated.
    3) Would the modulation of my J5ís improve if I replaced the DOT 4 fluid with thicker DOT 5.1 fluid?

  20. #20
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    Well I downloaded and read the caliper overhaul section in the Avid's Juicy Technical Manual and the piston slides out on a seal that is affixed to the cylinder in a countersunk groove. So I was wrong about a blemish in the cylinder causing the problem. Anyway the manual states that if pushing the piston back into its cylinder does not resolve the sticking and or slow return issue then the caliper will need to be rebuilt because the seal is worn out or deformed.

    My 07 J5 rear brake suffered from a sticky piston on my first ride and my wife’s 05 J5 has a slow retracting piston on her rear brake that cropped up after about three years of riding. The fronts on both the 05 and 07 J5’s have been trouble free so far. Somehow the length of the hydraulic hose affects the durability of the caliper seal. Maybe the longer line expands more and ultimately delivers less fluid pressure on the seal-piston assembly. Therefore, the seal it is less likely to get lubricated, which dries it dries out and causes the piston to stick or drag.

    I will try some silicone spray this weekend as a last dish attempt before I rebuild the caliper.

  21. #21
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    The warble isn't just an Avid hydro brake issue.

    My BB7's developed the turkey warble noise. I switched out to Alligator Serrated rotors and new brake pads. Noise is gone.

  22. #22
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    Quote Originally Posted by bwalton
    Somehow the length of the hydraulic hose affects the durability of the caliper seal.
    Or maybe, just maybe, the rear caliper gets a crapload more dirt on it than the front.

  23. #23
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    I spoke with a mechanic at a LBS about sticky pistons and he said that Avid, Hayes and Shimano brakes all develop sticky stick pistons. His shop sells the Juicy caliper rebuild kit for $45.00 and the Hayes kit for under $20.00, both of which include pistons. He did not give me a price for Shimano kits but instead said that the older LX and XT brakes only required cleaning to free up the stubborn piston. He recommended the new XT M775 brakes but qualified his recommendation by saying his shop has only sold four sets so far. He also said to steer clear of the new XTR brakes, which need to be rebuild often.

    I wonder if Avid will honor its two year after market warranty on an OEM brake that was installed on a new bike that is over a year old.

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