Cavitated shock – what causes it

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  • Cavitated shock – what causes it
  • Premier Icon ChrisI
    Subscriber

    I’ve just had my Fox Triad fixed by Mojo under warranty for making “squelchy” noises. On the worksheet, they have stated that the shock was cavitated and replaced the seal in the meter rod and IFP, then regased and reoild it.

    From what I can find on the net, cavitation is where air gets into the oil which causes the squelching or sucking noise and kills the damping a little.

    What I want to know is a little more detail of what happened to the shock and why when its less than a year old and not been used an awful lot this would have happened and if theres anything I can do to avoid it? Also what is IFP and meter rod? I assume these are part of the assembly to keep the nitrogen out of the oil?

    TIA

    Tim
    Member

    AFAIK, its when an internal seal within the shock allows the nitogen to mix with the oil, whcih then ‘foams’ under movement/heat build up and reduces the oil viscosity, and therefore afects damping rates.

    I may be talking out of my arse 🙂

    LoCo
    Member

    Internal float piston (IFP) separtes the oil and gas chambers, when seal goes you get mitro. in the oil causing inconsistant damping, it foams when you open the damper.
    The meter rod replacement also suggests the tiny ball bearing on the end of it that runs against the adjuster cam, had fallen off too as a result of the nitrogen pressue loss.
    Edit, the meter rod controls the adjustment of the propedal and runs from the adjusters to the piston and is lifted and lowered by a cam on the adjuter.

    Premier Icon ChrisI
    Subscriber

    Thanks for the replies guys. I assume there was nothing I could do to stop this and its just “one of those things”? Up until a week or two ago the shock was flawless and didnt make and discernible noise, until after a ride it was making a little noise but it was very cold so thought it could be that. After another mainly road ride to my parents it was really squelching and lockout didnt work, it was bobbing a lot. I assume something had literally let go and not worn out prematurely.

    Just want to avoid having it again – although Mojo were excellent, turn around in a couple of days and got the shock back to me for tonights night ride 😀

    LoCo
    Member

    Faulty seal caused the issue, the Triads are more prone to this issue than the RP23s.

    strike
    Member

    LoCo – I have an air shock which cavitated only 5 months after being (fully) serviced. The service centre blamed it on dirt ingress, even though the shock air can was/is regularly removed/cleaned/re-greased, and has had no contamination inside at all.

    What’s your take on this?

    LoCo
    Member

    TBH, I’d have to inspect the shock to make a judgement on that one Strike, as I’m sure you can appreciate I don’t really want to comment on other ‘tuning’ companies policies. 😀

    hughjengin
    Member

    I wonder if thats what the issue with my Fox Float R shock. It literally sounds like its full of grit or something (which it isnt becasue I did a recent air sleeve service on it and it was clean as a whistle) it sounds almost crunchy, for the first 5 or so compressions and then it goes perfectly quiet after that ??? its been stumping me whats causing it. At first I even wondered whether it was the shock and not some pivot full of crud, or something. damping and rebound seems to still work ok, not noticed any extra bobbing or blowing through the travel, and rebound dial still has the same responses as I would expect. So not overly concerned unless someone knows different. I suppose you could describe it as squelchy, but it sounds more like crunchy to me ! And then strangely it goes quiet after a half dozen compressions ?? Any clues anyone ??

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