Fox RP2 - big trouble.- Mtbr.com
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  1. #1
    i32
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    Fox RP2 - big trouble.

    Hi all!
    I have the RP2 2008 MY Med rebound / High compression on my Specialized Pitch.
    Some days ago i'm going to service to change oil.
    Returned with a trouble.
    In a simple: no rebound damphing over high speed compression, when propedal is ON.
    When the shock get a fast compression and rapidly released, it's kicking up, with hit sound and same feeling on the frame.
    When the shock compressed more slowly, or stay compressed a moment, all ok - it's works with dialed rebound setting.
    When propedal is off - all is ok.

    Me and major techician of a local Fox service have no ideas about. Shock was totaly rebuilded, filled with nitro, we are tryed some propedal spring options, different type of oils - no result.

    Have some ideas from MTBR?
    PS: sorry for bad English (
    PPS: FoxFactory, Push, TFT - noone is not available in/for our country cause customs specifics. Service, then we have, is a authorised by Fox, but it's only local service.
    Last edited by i32; 06-25-2011 at 01:29 PM.

  2. #2
    PMK
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    Sounds like the tech either got some parts installed incorrectly, the damper does not have enough fluid, or the possibly, but I doubt this is that the IFP is not at the proper depth.

    The other possibility, and I don't know if the tech tore the damper apart 100%, but maybe he positioned the damper end fitting and the PP shaft, rebound shaft, main shaft together out of alignment.

    PK

  3. #3
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    My first though is that the tech mistakenly removed a shim from the rebound circuit. That is the only thing that would explain why the rebound is to fast only on big hits(since a weaker shim stack would blow off easier on big hits). But I dont know why it would feel better with propedal off.

  4. #4
    i32
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    Thanks!

    But... important notice, that forgotten: damper assembly was not rebuilded previously, it was disassembled first time after problem with rebound was occured.

    Cause to change oil was a chawing sound, a nitro+oil coctail in result of blowing IFP o-ring.

    PS: mullen119 thanks, but i did'n say about big, here is no rebound when fast.
    For example, if the shock compressed then take a moment, then uncompressed, rebound is ok, as dialed. If it was compressed and rapidly uncompressed, it kiks with no rebound damping. And it was only over propedal. With propedal off, all is ok
    Last edited by i32; 06-25-2011 at 01:24 PM.

  5. #5
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    Sounds like not enough IFP pressure. It is cavitating when you need to make a lot of compression damping force and that causes the shock to shoot back.

    Take the air can off. How much force does it take to compress the shock 1mm. This force should be the IFP pressure times the shock shaft area (approx 3/8" diameter?) The IFP pressure is supposed to be around 300+ psi.

  6. #6
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    Take the air-sleeve off and try to compress it by hand. How much force does it require?

    This is a way of testing your IFP pressure.
    Owner of www.shockcraft.co.nz, Mech Engineer, Tuner, Manitou, Motorex, Vorsprung EPTC, SKF, Enduro
    www.dougal.co.nz

  7. #7
    i32
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    Quote Originally Posted by Dougal View Post
    Take the air-sleeve off and try to compress it by hand. How much force does it require?

    This is a way of testing your IFP pressure.
    I have no dynamometr or any other device too measure a force, but without aircan it's require a some noticable force to be compressed by hand, when released, it uncompressing by itself.
    When propedal turned on, it's looks like very hard to compress it.

  8. #8
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    Quote Originally Posted by i32 View Post
    I have no dynamometr or any other device too measure a force, but without aircan it's require a some noticable force to be compressed by hand, when released, it uncompressing by itself.
    When propedal turned on, it's looks like very hard to compress it.
    How big is the shaft and how much (roughly) of your body weight is needed to get it moving from full extension?
    Owner of www.shockcraft.co.nz, Mech Engineer, Tuner, Manitou, Motorex, Vorsprung EPTC, SKF, Enduro
    www.dougal.co.nz

  9. #9
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    Quote Originally Posted by i32 View Post
    I have no dynamometr or any other device too measure a force,
    Use a bathroom scale.

  10. #10
    i32
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    Finaly, thanks guys.

    Without rebuilding i remove aircan, purge IFP, make DIY from basketball&med needles, make a drilled hex for rubber pressing, add this things to my pump and inflate IFP to 300PSi (max for my pump) with air. Problem is gone.
    Another problem occured - sound, like a "poo" in the end of stroke, when closely to bottom out, but it's a little, i think, and it may hunted during rebuild some time later, when i'm return from mountain trip.

    God bless MTBR! )

  11. #11
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    Quote Originally Posted by i32 View Post
    Finaly, thanks guys.

    Without rebuilding i remove aircan, purge IFP, make DIY from basketball&med needles, make a drilled hex for rubber pressing, add this things to my pump and inflate IFP to 300PSi (max for my pump) with air. Problem is gone.
    Another problem occured - sound, like a "poo" in the end of stroke, when closely to bottom out, but it's a little, i think, and it may hunted during rebuild some time later, when i'm return from mountain trip.

    God bless MTBR! )
    Maybe you have too little oil and you're hitting the floating piston.

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