On these leaking Fox air shocks.- Mtbr.com
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  1. #1
    TNC
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    On these leaking Fox air shocks.

    I just got my DHX Air back from Fox for that stuck down condition. The repair and parts description said it was a failed Q-Ring...that's "Q" not "O". I just did a search on Google for "fox q-ring" and got a pic of a Fox shock with a part marked q-ring seal #22. Even though the shock looks like something else in Fox's line other than a DHX, the part number is the same as mine except for the size designation which is probably logical. Can anyone tell what that part's function appears to be? I know it's a seal, but can anyone tell the specific areas that it is sealing for and against?...and ponder a guess where the term Q-Ring instead of o-ring might come from? I'm going riding now to see if I can blow this thing up again...LOL!

  2. #2
    Old man on a bike
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    My search came up with a fox service pdf that talks about the q ring fitting into a q lip, imagine it's an o-ring with a shape other than round, perhaps a small lip (male on the ring, female on the q-lip it fits into?)...
    "...the people get the government they deserve..."
    suum quique

  3. #3
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    Quad Rind

    A Quad Ring serves the same purpose as a standard o-ring but offers lower friction due to it having a smaller overall sealing footprint than an o-ring.

    I attached a pic of the location of the seal in question as well as a bad pic of what the profile looks like. Instead of having a round surface like an o-ring, it has two "lips" per side that seal against the surface.

    Darren
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    Thanks Darren!

    How do you find time to reply to stuff like this?

    What a workaholic.

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    Must eat food

    Lunch, my MTBR time.

    Workaholic = no chance, we play for a living!

    Darren

  6. #6

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    Why are these shocks getting stuck down so much? Even my Float from two years ago did the same thing.

  7. #7
    TNC
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    Way to go, Darren. That's better info than I could have hoped for. That's a tricky little design there. Thanks.

  8. #8
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    quad rings-yuck

    Quad rings, have some benifits, but are very easy to damage during install, any small nick will lead to a leak, and tend to grab and tear with the wrong surface finish. O-ring design, is covered in detail at applerubber.com, for any design engineer it is the place to go for o-ring help.

  9. #9
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    I'll try to explain this as I understand it...

    Quote Originally Posted by Jerk_Chicken
    Why are these shocks getting stuck down so much? Even my Float from two years ago did the same thing.
    Fox air shocks use a dual air chamber design similar to Rock Shox rears. But they are not seperately adjustable like the Rock Shox Dual Air system. Even some of the new Rock Shox forks have a "non-adjustable" system that they call Single Air, based on the same idea. As you fill the main chamber of your Fox a percentage of the air in the main is bled off into the negative chamber. Don't ask me how they determine the percentage or how this is done exactly, but I am sure that it is a one way valve of some kind or other. Anyway, the negative chamber acts just like the RS set up by putting resistance on the positive chamber to make it easier to start the shock into it's initial stroke and over come static friction. The Q seal seperates the main and negative chambers from one another as well as sealing them. When that seal goes bad it allows the pressure between the negative and main air chambers to equalize. This forces the piston to a position approximately half way between the bottom of the stoke and full extension. The shock is effectively "stuck down" and unable to fully extend because of the equal pressures between the two chambers.

    My guess would be that those seals are either getting nicked during assembly as LititDude mentioned or perhaps Fox is getting seals that are not all they should be.

    That's the simple down and dirty of it.

    Good Dirt
    "I do whatever my Rice Cripsies tell me to!"

  10. #10
    TNC
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    +/- valve

    Quote Originally Posted by Squash
    Fox air shocks use a dual air chamber design similar to Rock Shox rears. But they are not seperately adjustable like the Rock Shox Dual Air system. Even some of the new Rock Shox forks have a "non-adjustable" system that they call Single Air, based on the same idea. As you fill the main chamber of your Fox a percentage of the air in the main is bled off into the negative chamber. Don't ask me how they determine the percentage or how this is done exactly, but I am sure that it is a one way valve of some kind or other. Anyway, the negative chamber acts just like the RS set up by putting resistance on the positive chamber to make it easier to start the shock into it's initial stroke and over come static friction. The Q seal seperates the main and negative chambers from one another as well as sealing them. When that seal goes bad it allows the pressure between the negative and main air chambers to equalize. This forces the piston to a position approximately half way between the bottom of the stoke and full extension. The shock is effectively "stuck down" and unable to fully extend because of the equal pressures between the two chambers.

    My guess would be that those seals are either getting nicked during assembly as LititDude mentioned or perhaps Fox is getting seals that are not all they should be.

    That's the simple down and dirty of it.

    Good Dirt
    The concept and design of that valve system is fascinating. I was under the impression that a stuck down was likely caused by the valve failing, but your description of the q-ring failing seems more likely...especially after seeing what it looks like. That looks like a lot of contact area too.

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