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  1. #1
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    Fox DHX5 Air Bleed

    Howdy folks. I bought a DHX5 that had a lot of air in the damping circuit so decided to dive in and sort it out. I came across some good info online that other folk had put up though much of it was for the coil version, and the air appears a little different in that it's inverted by comparison and thus slightly more involved because of an additional shaft volume and orientation issue. I'd read beforehand about the possibility of submerging the entire unit in oil to do this but I didn't have this much oil around, and also didn't really want to have to do it that way, so I came up with the following...

    Whether there be better ways to do this I don't know (in hindsight there are likely a number of possible methods), but can say that the following worked well for me and required very little oil and only basic tools to complete. So, for what it's worth, here are a bunch of images and short descriptions of what I did;

    * You can click any image for the full resolution version *

    The first 4 images just show the hardware I started with prior to getting the process rolling. I'd removed some parts for cleaning and so are not shown here. Aside from the main air piston seals I'd also removed an o-ring from the bottom out adjuster to make things a little easier further on (not essential).





    To use only minimal oil to complete the procedure I used an empty pill bottle with bottom cut off and fitted some draft strip foam to allow for it to slide/seal onto the main shaft;



    Clamping the assembly upright using my truly amazing vice + plastic chair. Nothing but the highest tech here...



    1. Greasing an o-ring in preparation.

    2. With the floating piston removed from the piggyback I introduce as much new oil into the system as I can at this point. This is mainly to effectively flood the whole piggyback & oil ways to help with bleeding later on.



    With valve core removed I hand tighten the bottom-out assembly into the piggyback. Once done I continue to pour oil into and onto the damping piston side so that both sides are about as full with oil as can be and then close the piggyback side with a dust cap.



    On the main piston shaft near the eyelet there's a very handy screw that's hidden under a little white plug. Pop that white plug off to reveal a 4mm grub screw. Unscrew that and there's a little rubber bung that seals it off underneath. Pop that out to effectively open up the shaft volume for bleeding later on.

    Now gently slide the shaft onto the oil piston/air piston, screw it up tight, then push the shaft down into its stroke (slowly to minimise foaming the air/oil inside).



    Pop on ghetto oil reservoir and add oil. Not much oil was needed, maybe only 50cc or so here. At this point it's a pretty simple process of sliding the shaft up/down to gradually exchange oil for air in the system.

    I spent about an hour at this stage pulling (pushing) air out, including leaving it to settle here and there. It's very much like bleeding hydraulic brakes and is easy to get an idea of how well things are going by just listening for the obvious sound of air bubbles shifting about, and observing bubbles ejected into the oil reservoir. After a while when things were feeling nice I dialed in a load of rebound to add resistance to pulling the shaft back up its stroke. This seemed to operate similar to pulling on a syringe when doing hydraulic brakes in that (I guess) it causes any tiny air bubbles in the oil to expand and float up faster towards the top of the shaft, and thus into the reservoir. I also tilted the assembly about and gave it a tap/knock here and there to help loosen any bubbles trapped in the system. Doing all this got it to a point where I was confident it was well degassed.



    1. Here I extended the shaft fully, tilted the assembly back, slid the reservoir down to give access to the grub screw, then carefully popped the rubber bung in the hole without introducing any air (easy enough) and screw the grub screw back on to seal it up.

    Now the whole lot is sealed tight and so you should have a very strong hydraulic lock assuming most of the air is out. I could barely compress the shaft ~1mm at this point.

    2. Here I remove the bottom-out adjuster to access the piggyback again. There were actually some small bubbles stuck to some surfaces in the piggyback base so I prodded those loose with a zip tie. In hindsight it might be worth gently pushing the shaft into its stroke a small amount at this point to push any potentially trapped air bubbles around the ProPedal valve section into the piggyback volume, making sure to return the shaft to full extension prior to reinstallation of the IFP.



    1. Ready to reintroduce the IFP.

    2. With the centre screw removed I pop the IFP back in.



    1. Here I set the IFP depth to 33mm for this 190x50mm (2 inch) stroke shock unit (based on info gleened on teh intertubes ), re-add the centre screw to seal it up, drain the excess oil, and added some 85w gear oil for happy days.

    I'd be careful not to cycle the main shaft at this point, or at least only very gently if doing so as the piston looked to wiggle up/down unevenly (with potential to break seal) without the usual "75-200psi" pressure backing it (I presume pressure would normally keep this in check ).

    2. Reassembling bottom-out to piggyback and repressurising.



    Viola! It's at this point I can cycle the shaft pretty hard and check to see if it at least feels alright. Good news is it felt bang on, there was no sound of air in the system at all and it all felt very slick. I'm pretty confident the procedure has worked well at this point, and so just the nice easy air can reassembly to do now.




    I can confirm all feels well after completing everything and installing it on the bike. In comparison to what the unit was like beforehand it's a lot better. It's virtually silent in operation now when bouncing on the bike other than a touch of valving whistle. So damn good. I'm just glad it was all a relatively painless process that even a n00b like me could pull off with only minimal tools and experience.

    Hope someone finds the info useful.
    Last edited by EmanResu; 02-21-2009 at 01:46 AM.

  2. #2
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    Looks like here is another bleed port at the other end as well. You can see it in this cut away pic: http://www.cyclingnews.com/tech.php?...HX_Air_cutaway

    IIRC one the guys on RM (Udi maybe) used a hollow bolt from the bottom of a boxxer to thread into the bleed hole you used. He then attached a syringe with a hose to the bolt to pump oil back and forth, working the oil out.

  3. #3
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    Nice image. I did come across that screw before starting the bleed above as I depressurised both chambers and then, out of curiosity, unscrewed that Allen head to try to determine what it was as I couldn't find info on it anywhere. What happened then was it blew a shitload of oil out under pressure into my face and halfway around the room. It wasn't the wisest of moves... and pretty much ruled out me being able to measure IFP depth before I started the bleed.

    I know there are probably a good number of ways to bleed these now, as you mention, using any combination of the 3 points in the system. My options were a bit limited really as I didn't have anything capable to syringe in that way, and tbh really wanted to break the unit down anyway to flush/clean it out properly, so it worked out OK for me. Anyone not wanting to go to such lengths could indeed simplify the process no doubt.

  4. #4
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    Two big 'ol thumbs up to you for getting into the shock and fixing it yourself. I am always dumbfounded at how little tech info is available from bike component mfg. and that is 10 fold when you start talking about suspension.

    Just trying to add some more info to your great thread.

  5. #5
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    Thanks, really appreciate the comment. I know very little myself but have found the bits of info folks post online including images have helped me a lot before venturing into stuff like this, so I'm just trying to offer a bit in return (even though it may not be the best advice I give).

    I don't like how some manufacturers appear to restrict service information from the public and a part of me posting such is indeed a small act of retaliation in that regard. So if what's posted can help someone like me get in there and fettle things on their own back and probably learn a lot from the experience, then that's cool. [/seriousness]

  6. #6
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    This is a brilliant write up! Ask a mod to sticky this into the suspension maintence thread, it should be!!

  7. #7
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    Nice work.

    Adding the link To Udi's how to.

    http://www.ridemonkey.com/forums/sho...d.php?t=201454

  8. #8
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    Cheers Nick_M2R / Furrner.

    Had a root about for some IFP depth values and came up with the following numbers;

    Code:
    Metric ;
    190mm, 50mm = 32mm
    200mm, 50mm = 32mm
    200mm, 57mm = 33mm
    215mm, 64mm = 34mm
    222mm, 64mm = 34mm
    241mm, 76mm = 38mm
    
    Imperial ;
    7.500, 2.00 = 1.25
    7.875, 2.00 = 1.25
    7.875, 2.25 = 1.30
    8.500, 2.50 = 1.35
    8.750, 2.50 = 1.35
    9.500, 3.00 = 1.48
    The metric values are rounded slightly to convert from imperial but are very close. They may be different for coil versions, I don't know. * Don't quote me on them.*

  9. #9
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    EmanResu you save a lot of money and time for me! Good jub!

    I rebuild my shock today and he's working much much better.

    But, i have a one question that don't give me to sleep well. in regular air sleeve maintenance i'm relieves both pressure valves, because it's much more easy to put air sleeve back. I thus do not change IFP depth?

  10. #10
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    Quote Originally Posted by GR_Russia
    EmanResu you save a lot of money and time for me! Good jub!

    I rebuild my shock today and he's working much much better.

    But, i have a one question that don't give me to sleep well. in regular air sleeve maintenance i'm relieves both pressure valves, because it's much more easy to put air sleeve back. I thus do not change IFP depth?
    I'm not too sure what you mean exactly so forgive me if I read you wrong. I think that if all you have done is service the airsleeve then no, you shouldn't have to recalibrate the IFP depth (I did this also as it made it a lot easier ).

    If afterwards though you then found a lot of air in the damping circuit then it could be possible (small chance maybe) that air managed to pass the IFP seal and into the damping oil as I *think* (i really don't know if true) that usually the IFP would need pressure acting on it in order to keep it properly stable (and thus sealed) as it slides up & down the piggyback when cycling the shock unit (aggressively). This might be a reason why it's stated that it should never be ridden without minimum air pressure in the piggyback (just a theory). I think it should be fine though when just using minimal pressure to help with screwing the airsleeve back on.

  11. #11
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    Quote Originally Posted by Nick_M2R
    This is a brilliant write up! Ask a mod to sticky this into the suspension maintence thread, it should be!!
    I added this thread to the Fork and Shock Service Information sticky thread.

  12. #12
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    Quote Originally Posted by EmanResu
    I'm not too sure what you mean exactly so forgive me if I read you wrong. I think that if all you have done is service the airsleeve then no, you shouldn't have to recalibrate the IFP depth (I did this also as it made it a lot easier ).

    If afterwards though you then found a lot of air in the damping circuit then it could be possible (small chance maybe) that air managed to pass the IFP seal and into the damping oil as I *think* (i really don't know if true) that usually the IFP would need pressure acting on it in order to keep it properly stable (and thus sealed) as it slides up & down the piggyback when cycling the shock unit (aggressively). This might be a reason why it's stated that it should never be ridden without minimum air pressure in the piggyback (just a theory). I think it should be fine though when just using minimal pressure to help with screwing the airsleeve back on.
    You understood me right, yep. Simply, when I unscrew bottom out i has found IFP displaced. The depth of IFP was only 12mm. It became food for such thoughts

  13. #13
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    Quote Originally Posted by GR_Russia
    You understood me right, yep. Simply, when I unscrew bottom out i has found IFP displaced. The depth of IFP was only 12mm. It became food for such thoughts
    12mm doesn't sound right at all. Are you sure that the shock was extended fully before you measured? If it wasn't resting at full extension and was instead pressed into its stroke then the IFP would measure short like that. If you can feel a lot of air in the damping circuit then maybe air passed the IFP seal, but really I would have thought that might be hard to achieve unless it was rode without sufficient pressure in the piggyback. If the damping circuit doesn't feel/sound like it has air in it then I can only imagine that either the unit was pressed into its stroke when you measured, or you have too much oil in the damping circuit and still need to set IFP depth (did you actually bleed the damping circuit here or have you only serviced the airsleeve?).

    I'm noooo expert but I'll try to help if I can.

    ---

    @All Mountain : nice one

  14. #14
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    Well, i think when i unscrew the bottom out in process i compress the shock and it could be the main reason why IFP wasn't on the place.

    Anyway i completely change oil in my shock with correct IFP depth

    P.S. EmanResu can i use your illustrations pics for Russian forum? I will put your copyright on them

  15. #15
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    EmanResu, you rock!

    Great write up!

    P

  16. #16
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    Quote Originally Posted by GR_Russia
    Well, i think when i unscrew the bottom out in process i compress the shock and it could be the main reason why IFP wasn't on the place.

    Anyway i completely change oil in my shock with correct IFP depth

    P.S. EmanResu can i use your illustrations pics for Russian forum? I will put your copyright on them
    Good to hear you got it sorted. I think if the airsleeve was installed prior to measurement of IFP depth then it would be essential to have the main air chamber pressurised in order to keep the negative air spring from sucking the shock down in its travel. I don't know if you did it with or without the airsleeve installed, but either way it's important to keep the shock extended fully to ensure the IFP rests at its maximum depth before measuring it.

    And please go right ahead and use the images for whatever you want if you can find use for them. I don't care for copyrights on them. Cheers.

  17. #17
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    What about the Nitro re-charge?

    Hi,

    Just reading through your tutorial, as I'm about to embark on a DXH Air service myself. I admit, I'm a noob as well when it comes to Fox suspension.

    I spoke with a buddy at the LBS & he gave me the "trust me, you don't want to go there" warning when I asked about doing a full service. He handed me the air sleeve service kit with a smile & recommended I stop there.

    Apparently, the dampening chamber is charged with nitrogen at ~300psi & the only way to get it properly put back together with the nitro re-charge is to send it to Fox (or sim. operation).

    Can anyone with some experience shed some light on this?

    Thanks

  18. #18
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    Quote Originally Posted by drewachabal
    Apparently, the dampening chamber is charged with nitrogen at ~300psi & the only way to get it properly put back together with the nitro re-charge is to send it to Fox (or sim. operation).
    There is no nitrogen in the DHX Air. Your buddy is referring to the "inline" shocks which do have nitrogen or the older RC models.

    Where you add "boost" air is where the nitrogen would be on your shock. But they gave an air valve to add air

    P

  19. #19
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    Thanks P!

    I guess it's full steam ahead.

    One more question - what type / viscosity of oil is recommended?

  20. #20
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    Hey there. As Mr. P mentioned there is no nitrogen charge in there, only oil and air. As far as the difficulty level, imo it's a pretty simple, straight-forward task - not complicated at all - though I'd just be careful as you're working on it to avoid inadvertently damaging anything.

    Re: Oils; I used 'Castrol Synthetic Fork Oil' 5w when I did the above, though I did it again just recently but with 10w this time. I think the more precise measure of the viscosities I used are as below (data pulled from http://www.peterverdonedesigns.com/);

    Code:
    Fox 7wt Oil (Torco RSF Medium)
      cSt@40	31.82
    Castrol  5wt Synthetic Fork Oil
      cSt@40	28.00
    Castrol 10wt Synthetic Fork Oil
      cSt@40	42.00
    The original Fox oil is (as far as I know) the Torco RSF Medium there listed as 7w, so of the 2 oils I've used so far both fall either side of that weight-wise. I don't imagine this causes any particularly negative side effects, just minor differences in damping and propedal values (e.g. running 8 clicks rebound on 5w oil might equate to only 5 clicks on 10w). I guess I could have just mixed the two weights to produce an equivalant ~7w but haven't seen a need to really (I was also interested to see what differences there were in how they operate).
    Last edited by EmanResu; 04-30-2009 at 10:07 AM.

  21. #21
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    Alright! Total success with my re-build. Thanks to EmanResu for the great pics & instructions.

    A couple tweaks from his method that may help others:

    1. The small panhead allen screw near the rebound adjuster is a great way to relieve the pressure in the dampening side while containing/controling the inevitable spray of oil. I just shot it into a rag.

    2. I didn't have a spare pill bottle handy to rig up the oil feeding into the dampener, so I stretched a piece of road tube around the end of the dampening piston & a syringe from a Juicy brake bleed kit. Worked great.

    I tried to set up a brake bleed scenario to really pull the air bubbles out of the oil - one on the end of the dampening piston & one on the end of the boost chamber - but there wasn't enough air volume available in the Avid syringes to do so. If you can find some high volume syringes, you're golden.

    Anyways, it was not hard at all & the replacement seals kit from Fox was only $10 at my LBS.

  22. #22
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    Quote Originally Posted by EmanResu
    Cheers Nick_M2R / Furrner.

    Had a root about for some IFP depth values and came up with the following numbers;

    Code:
    Metric ;
    190mm, 50mm = 32mm
    200mm, 50mm = 32mm
    200mm, 57mm = 33mm
    215mm, 64mm = 34mm
    222mm, 64mm = 34mm
    241mm, 76mm = 38mm
    
    Imperial ;
    7.500, 2.00 = 1.25
    7.875, 2.00 = 1.25
    7.875, 2.25 = 1.30
    8.500, 2.50 = 1.35
    8.750, 2.50 = 1.35
    9.500, 3.00 = 1.48
    The metric values are rounded slightly to convert from imperial but are very close. They may be different for coil versions, I don't know. * Don't quote me on them.*

    Booya - that's what I was looking for!!
    Great post and thanks for the info

  23. #23
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    Quote Originally Posted by drewachabal
    I didn't have a spare pill bottle handy to rig up the oil feeding into the dampener, so I stretched a piece of road tube around the end of the dampening piston & a syringe from a Juicy brake bleed kit. Worked great.
    I like that idea, I'm guessing you could even expand on that and have one on the Boost (IFP) chamber too which I think should allow you to cycle oil through the whole system (EDIT: Ignore me, I realise now that's exactly what you said in the following paragraph *doh*).

    Many possibilities … and good to see folks experimenting with their own (as I certainly don't think mine the best, merely sufficient).
    Last edited by EmanResu; 05-19-2009 at 02:21 AM.

  24. #24
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    Cheers for the info. My shock has been making some air noise for a while now, I must have cycled it with no pressure in the boost valve (you'd think they'd just put 2 o-rings on the IFP which would solve the problem of going off-camber inside the piggy and letting air in). Refilled it with some 10wt Motul Factory Line which is a bit thicker than factory but not by much.

    I went totally ghetto and did it without a vice - all by hand which made it a little tricky but still achievable. I also just used the air sleeve as an oil reservoir over the top of the damper shaft which worked fine - only problem being that there wasn't much space to get the plug back into the bleed port, but a pair of very long tweezers worked.

    There is still a little air in there but much less than what it had - i'll cycle it again after a few trail runs. I'm happy as well 'cos i know now that the IFP is at the right depth.

    Also had a look at the shim stack and rebound port when i was in there. Looks easy enough to change the shims but you have to fill and bleed each time - a little messy.

  25. #25
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    Quote Originally Posted by DJR_9000
    (you'd think they'd just put 2 o-rings on the IFP which would solve the problem of going off-camber inside the piggy and letting air in)
    I've wondered about that o-ring too. To me it looks as though the IFP was originally designed to house a 'quad seal' like the main piston as that o-ring just doesn't seem to fit right. I was considering throwing 2 rings in there also for this reason.

    Quote Originally Posted by DJR_9000
    Refilled it with some 10wt Motul Factory Line which is a bit thicker than factory but not by much.
    I made a mistake above I think if you're basing your thoughts on the 7wt mentioned being standard. As I understand it now I believe 10w is the new default for the DHX though I don't know what brand so am unaware of a viscosity value to aim for. No big deal either way I don't think, I've run a 5w and 10w a bit now and can't say I've noticed any huge difference between them.

    Quote Originally Posted by DJR_9000
    I also just used the air sleeve as an oil reservoir over the top of the damper shaft which worked fine
    This is genius, can't believe I never thought of that! I'll definately be nicking this idea next time I do mine.

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