Very worn stanchions on a Fox 36 Float R. Unsafe?- Mtbr.com
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  1. #1
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    Very worn stanchions on a Fox 36 Float R. Unsafe?

    New to the forum but lurking for a while. Tons of great info on here, most of my research is via this forum.

    Before this gets too heated about due maintenance vs wear vs manufacturer design I just want to give some background:

    I picked up my first full suspension bike a little over a month ago, a well-used 2009 Rocky Mountain Slayer sxc-50. I was very excited about the bike and knew I had some serious maintenance to perform, it was off eBay and came with frame bearings so I expected wear and tear.

    I took it for one ride so I would know what it was like before obvious due maintenance (frame pivots need grease, fork oil probably old, rear shock has almost zero dampening).

    I started by sending my rear shock off to Risse as I figured it would need more than an air sleeve and I don't mess around with high pressure nitrogen.

    Now to the meat of my question for you guys:

    I got into the front fork which I knew had poor maintenance and the stanchions have very significant wear (I can feel and see grooves, maybe 1/32 to 1/64" deep wrapping half the diameter) and the oil was something like either pitch or peanut butter with a little fluidity. Obviously this had me concerned. With some difficulty, I fitted new wipers, filled both the damper and forks with fluid, giving the bottom a little extra (50mL forks, 100mL damper).

    I know these forks are never going to work as designed without new stanchions and bushings. I haven't gotten a bid on the costs, but I imagine around $300 in parts.

    Is significant stanchion wear a concern for injury riding this bike? Do you guys see many people breaking stanchions riding bikes like this within the category "all mountain" (ie not taking the chairlifts and riding hard DH)?

    I am willing to ride as is while I save for either a different fork or replacement parts, but not if safety is a genuine concern.

  2. #2
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    I would say at this point, I would say you have done what you need to do. I have never heard of fox forks snapping and would not be too concerned about that. Are those the correct oil-volumes?
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  3. #3
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    That's pretty fatal wear, even with new oil the linings of the bushings are gone so you've got metal to metal contact. The steel body of the bushings will scrape away the bare aluminium of the fork stanchions, which will fail sooner or later. I certainly wouldn't ride it knowing the condition of the internals was that bad.

    Basically it's time for either repairs or new fork.

  4. #4
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    Thanks for the quick replies. I realized that I probably can't reliably measure 1/32 vs 1/64 with my fingers. I will open up the fork again in a couple of days to get some pictures and take out a caliper to get an actual measurement of the difference in diameter in the worn vs non-worn areas.

    Vespasianus: I used a slightly higher oil volume as I had read the 30mL recommended may be not quite what would be optimal, but is used to keep the fork light. The overall air volume is so great, I figured that the compression effect would be minimal even if I had 50mL (20mL air volume lost).

    FTS: Would new bushings be useful here, even if the stanchions have grooves like an old disc rotor? I know replacement is optimal, but if I can't really drop $800 on a new fork I am trying to figure out if this is damaging to anything else on the fork (stanchions and bushings already shot) or if I am about to find my teeth on a rock, but I guess it sounds like these won't be snapping anytime soon.

    I want to do everything I can functionally for the bike. Honestly, I haven't ridden consistently since the late 90s, so even with this fork acting like garbage on the first ride, it felt amazing compared to old tech. My expectation is that functionally, the worn stanchions will make the fork sort of "sticky" giving poor response to small bumps, but the fork could handle middle and big hits just like it was designed.

    I plan to stick to a schedule keeping up with Fox's service intervals, even if they are a bit short.

  5. #5
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    Quote Originally Posted by seylerc View Post

    FTS: Would new bushings be useful here, even if the stanchions have grooves like an old disc rotor? I know replacement is optimal, but if I can't really drop $800 on a new fork I am trying to figure out if this is damaging to anything else on the fork (stanchions and bushings already shot) or if I am about to find my teeth on a rock, but I guess it sounds like these won't be snapping anytime soon.
    New bushings certainly won't do any harm, it will end the metal/metal contact which should be your priority!

    It's worth your time watching Ebay for a new stanchion/crown assembly, they crop up on Ebay fairly regularly and you can have a new set under the rrp, or depending on how bad yours are (they sound pretty bad) a slightly worn set for a lot under the rrp.

  6. #6
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    I don't think you want to be the guy that figures out 'exactly' how deep you can push those grooves into the stanchions before something fails. I wouldn't ride it like that even on easy trails. Failure up front is a bad, bad thing. A new CSU will run you ~$200-250 and will let you ride with total confidence. It's not worth risking a life-changing crash to save a few bucks.

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  7. #7
    Udi
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    There is no point replacing the bushings or CSU assembly individually, as changing one without the other will result in rapid wear of the mating part.

    For a proper solution, you will be paying for the CSU, bushings, and service costs for fitting the bushings (it is not a DIY job for most).

    With those costs added up you'll be better off buying a new fork, or a used fork that has been carefully checked for wear.

    In the meantime, I think you're going to struggle to find professionals who will tell you your fork is fine and safe to ride - as short of running engineering analysis it is impossible to say at which point of wear the fork will fail to be structurally sound. However, in all honesty, I highly doubt your fork will just snap while riding due to bushing wear on the stanchions. The wear is perpendicular to the direction that would encourage a stress fracture, and in my opinion would (likely) have to be deeper than 1/64in to weaken the stanchion enough to fail in normal riding use.

    In short, you'll probably be fine to just do regular oil changes and deal with any minor leaks until you can afford a new fork. It's most likely not going to break. But obviously the risk is yours and no one can guarantee anything.

    Hope that helps.

  8. #8
    Udi
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    To elaborate a little, you cannot merely replace the CSU, because the wear in the bushings will cause small levels of misalignment between the surfaces of stanchions and bushings. These small misalignments cause heavy localised loadings on the stanchions (compared to the regular distribution of load) and greatly accelerate wear as a result. The net effect is that your expensive replacement CSU will be ruined by your old bushings in short order, especially in your case, as bushing wear is clearly significant.

    Obviously this localised loading scenario is currently in effect also (as the stanchions and bushings are both worn), and is a contributing factor to the possibility of failure. I personally think you'll be fine for a while, but you can see how giving a definite answer would be calculation heavy, and thus the best you'll get is an educated guess.

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