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 off teh intertubes :thumbsup
, 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. 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.
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 off teh intertubes :thumbsup
, 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. 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.
