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  1. #1
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    Looks like piston sticking?

    On my ride at racoon mt. i noticed my rear disc making a rubbing sound, and upon further insp. it looks like the outer/left side piston is not returning to where it should be. This is on a set of Avid juicy 3's, can i spray it with auto type brake cleaner? What other maint. can be done to keep these working properly. Thanks for any replies.

  2. #2
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    Push them back w/ a flat screwdriver several times, see if that takes care of your problem.

  3. #3
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    spray with wd 40, (not for use with shimano though) let sit, then activate the lever a bunch of times

    if that doesn't fix it, the caliper is toast - ive seen this before, its not that uncommon

  4. #4
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    Quote Originally Posted by racerick
    spray with wd 40, (not for use with shimano though) let sit, then activate the lever a bunch of times

    if that doesn't fix it, the caliper is toast - ive seen this before, its not that uncommon
    Have you personally sprayed a MTB brake caliper w/ WD40? I'm curious to know if there is a negative side to it interacting with not only the brake fluid (once it gets around the caliper piston) but the seals as well. If it didn't contaminate the fluid it seems there is a good possiblity it may swell the seals. To the OP: I would definately stay away from automotive brake cleaner for an MTB application. I have a friend who used Tri-Flow on his sticking juicy ultimate piston. Seemed to work ok but then again he's had to do it a couple times since then so I dunno. Is there a specific gease/lube recommended for the caliper and or master cyl. piston(s)?
    holy...

  5. #5
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    Checking that the system is bled is usually the most productive first step. Once you're happy that the system is free of air and that the fluid is in good condition - DOT fluid thickens over time - then recheck for piston issues. If the problem remains, then start with cleaning the pistons and seals...

    DOT fluid or Silicone spray for cleaning DOT brake seals. Pads out; extend pistons;spray; clean with cotton bud; push carefully back into caliper with plastic tyre lever. Repeat a couple of times, wipe all excess fluid from the caliper interior, refit the pads and test the piston's operation. If you're still getting uneven extension/retraction then it's most likely time for a seal change.

    For the reasons mentioned by ver-T, and the additional problem of the oily residue it would certainly leave behind, I would say that WD40 and GT85 are almost certainly a no-no for cleaning brake seals.
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  6. #6
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    Well the screwdriver moved it some, it's not rubbing anymore. It still does not seem to go back inside the housing like it should. The WD-40 is kinda what i was wondering about, do pistons need to be sprayed with something to keep them clean and free of debris? What are some maint items i need to keep brakes working 100%? Do i remove wheel to keep any sprayed substances off rotor, like on auto brakes. I do most maint on all my vehicles SUV, bass boat, lawn mower, just not sure about how to treat mtn. bike. only been riding 6 mos. not familar with bike do's and dont's! Thanks

  7. #7
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    OK that is good info on how and what to use to service calipers! Thanks and i will let you know how it worked in a couple of days.

  8. #8
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    any system that uses DOT brake fluid can withstand a slovent based lubricant
    the brake fluid is more caustic than WD 40, so the seal will be fine yes i used it on a friend's avid system

    that's why i said not to use it on shimano systems, as it would damage the seals

  9. #9
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    Quote Originally Posted by racerick
    any system that uses DOT brake fluid can withstand a slovent based lubricant
    the brake fluid is more caustic than WD 40, so the seal will be fine yes i used it on a friend's avid system

    that's why i said not to use it on shimano systems, as it would damage the seals
    The EPDM seals in DOT based MTB brake systems are not damaged by glycol based brake fluid (DOT 3,4, 5.1). They are not rated for use w/ petroleum based products e.g. WD-40. I copied and pasted what I found.

    ETHYLENE PROPYLENE RUBBER (EPM, EPDM)

    Typical Trade Names:

    Nordel…………………………….E.I. duPont de Nemours

    Royalene……………………………………………Uniroyal

    Vistalon………….……………..Exxon Chemical Co. USA

    Epsyn………………Copolymer Rubber & Chemical Corp.

    Epcar……………………..………………B.F. Goodrich Co.

    Ethylene propylene rubber is an elastomer prepared from ethylene and propylene monomers (ethylene propylene copolymer) and at times with a small amount of a third monomer (ethylene propylene terpolymers). It was introduced to the rubber industry in 1961 and quickly won broad acceptance in the sealing world because of its excellent resistance to Skydrol and other phosphate ester type hydraulic fluids.

    Ethylene propylene has a temperature range of -65· to +300· F (-54· to +149·C) for most applications.

    EP IS RECOMMENDED FOR:

    Phosphate ester base hydraulic fluids (Skydrol, Fyrquel, Pydraul)

    Steam to 400·F (204·C)

    Water

    Silicone oils and greases

    Dilute acids

    Dilute alkalis

    Ketones (MEK, acetone)

    Alcohols

    Automotive brake fluids.

    EP IS NOT RECOMMENDED FOR:

    Petroleum oils

    Di-ester base lubricants.
    holy...

  10. #10
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    Steve - I had a sticky piston on my Juicy 7's. Just tried your method and it took about three cleanings but it worked great. My front wheel would only make about 3 revelotions before it stopped while up on it's stand. Now it rolls for almost 3 minutes.

    thanks for the tip.

  11. #11
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    can you take the pistons out all together (hope minin monos) clean them and put them back in?
    Rolling & Tumbling

  12. #12
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    Quote Originally Posted by SteveUK
    Checking that the system is bled is usually the most productive first step. Once you're happy that the system is free of air and that the fluid is in good condition - DOT fluid thickens over time - then recheck for piston issues. If the problem remains, then start with cleaning the pistons and seals...

    DOT fluid or Silicone spray for cleaning DOT brake seals. Pads out; extend pistons;spray; clean with cotton bud; push carefully back into caliper with plastic tyre lever. Repeat a couple of times, wipe all excess fluid from the caliper interior, refit the pads and test the piston's operation. If you're still getting uneven extension/retraction then it's most likely time for a seal change.

    For the reasons mentioned by ver-T, and the additional problem of the oily residue it would certainly leave behind, I would say that WD40 and GT85 are almost certainly a no-no for cleaning brake seals.
    Best way to extend only one pad at a time or extend both slightly for this cleaning?
    Fat, drunk, and stupid is no way to go through life son...

  13. #13
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    SteveUK,

    This is working great, thanks! I sprayed the sticking piston only and then just real gently squeezed the front brake lever while watching the pistons and they extended ever so slightly with each lever stroke. Once extended, I sprayed them both with the silicon spray and then cleaned up around the edges with Q-Tips, repeat a few times and then going to clean up with lint-free rags and isopropyl alcohol.
    Fat, drunk, and stupid is no way to go through life son...

  14. #14
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    Quote Originally Posted by Natedogz
    This is working great, thanks! I sprayed the sticking piston only and then just real gently squeezed the front brake lever while watching the pistons and they extended ever so slightly with each lever stroke. Once extended, I sprayed them both with the silicon spray and then cleaned up around the edges with Q-Tips, repeat a few times and then going to clean up with lint-free rags and isopropyl alcohol.
    Success! Your technique is good. If you want only to extend one piston, just leave the caliper bolted to the bike and use a plastic tyre lever to prohibit the movement of the other piston. You may be surprised with how far pistons can be extended without introducing air from the MC; although this will obviously be dependent on the specific brake. Just remember to push them both back flush with the caliper when you're done.
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  15. #15
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    Yes, I'm amazed how far out they can go without getting air in the system! While this helped, I ended up removing the piston cleaning (it looked clean though) and reinstalled with dot 5.1 brake fluid as lube. It is better than it was but still not as free as the other piston. We'll see when I take it for a ride.
    Fat, drunk, and stupid is no way to go through life son...

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