Specialized FSX Hydracoil conversion
WIP
 | |
| Time | 2 hours max |
|---|---|
| Difficulty | 8 / 10 |
| Tools |
Inbus key ? mm a few nuts or Adjustable spanner. |
| Material |
220 ml 10WT fork oil non freezing grease 2x rotary seals 28x35x5mm BASL 2x o-rings 8 x 1 mm a donor Hydracoil Judy M8 to M6 thread insert |
This howto refers to the Elastomer version of the Specialized FSX fork with "Rock Shox Judy inside". I think it would also work for the Elastomer Judys as they are very much the same. But I did not test that.
I did this conversion as I got a FSX fork without the original internal parts and I had a Judy XC 100 Hydracoil laying around for parts. As I don't like Elastomers and I have bad memorys of cracked open dampening cartridges it kind of came natural to convert to Hydracoil. Its the better system after all.
To find the fist version of the howto and a discussion, you may want to visit the corresponding forum thread: http://www.retrobike.co.uk/forum/viewtopic.php?f=6&t=341270
Contents
Pre conversion checks
Before you start converting your fork you might first try out a few things.
- First inspect your upper seal wipers. The original ones were made to keep the dirt out of the forks, they were not meant for keeping oil inside. They might do the job. But I would suggest to add new seals. See also "Problems that might occur" down below.
- Make sure your outer legs are "oil-tight" and by that I mean the bonded joint between the carbon tube and the dropout. To check, separate sliders tubes from the stanchions, seal the lower hole, fill with some evaporating fluid (I used break-cleaner) and put a bit of pressure inside (e.g. blow into the tube with your mouth, sealing it with your hand ;) ). See also "Problems that might occur" down below.
- Check for play between the stanchions and the bushings in the dip tube. Replace the bushings if needed.
The Conversion
This is the insides of a Judy Hydracoil 100 LT, that I used for parts.
The Elastomer Versions of the forks have a few differences in drop outs. First of all is the bore diameter for the allen bolts that hold the dampening rods. The older elastomere version bolts are M6, the newer are M8, hence the lager hole. Also notice that the space around the hole is less on the older Versions. So the adjustment cap will not fit.(upper: Hydracoil XC, lower: 95' Judys, middle: FSX)
The second difference is the stanchions endings. Old to the left, new to the right. The old stanchion versions have a snap ring to keep the dampener parts inside. The more modern version has a bent tube ending and that plastic part. It is the topout dampener so to say and I had to use a part from some other Judy instead. Sadly I dont know witch version Judys it came from, but I think it was a early Hydracoil one. The part shows in the pics 6 and 7.
I was using the old version stanchions. But you can also just use the newer ones. They have the same length and outer diameter and should fit the older version dip tubes no problem. Doing it this way you can keep all the dampening parts from your modern version Judys - no modification needed on the inside of the stanchions.
This picture is showing the differences between old and new dampening rods. Old to the left, new in the middle and to the right.
M6 vs. M8 Allen bolts. Luckily the last few mm do have the same outer diameter.
In the middle you can see the Allen bolt that has a bore to fit a small Allen key through. That small Allen Key is moulded inside a cap that fits over that m8 bolt. Sadly there wont be enough space in the old version dropout to use that cap. And the m6 bolts don't have enough flesh to make a hole big enough to fit that Allen key through. So there will be no "on the road" rebound adjustment available after the conversion. At least not without using tools.
M6 to M8 thread insert "problem solver"
This is how it all fits together. O-ring has to just fit over that rods end. The pictured o-ring is a bit too large (see also next pic).
Then the thread insert into the dampening rod.
Note the black topout thingy laying above the assembly.
Here you can see the o-ring I used is a little bit too thick. It worked but ideally it should not stick out sideways. And this is basically it. Put it all inside the stanchions, secure with the snap ring. Bolt it into the dip tubes and fill with 110 ml 10wt fork oil (if your weight is 80+ kg). Check for oil leaks.
Travel adjustment
This is how you adjust the travel together with the build height. These white plastic spacers fit either at the ends of the springs or over the dampening rod as seen in the picture. Using the right length springs it is always 2 spacers per side. With both spacers down on the dampener rod the fork has something around 70mm of travel. With the spacers on top of the springs instead its 100mm. Too much for my trusty old retro steed.
Comparison of my FSX tuned to 70mm vs. Judy DH 80mm.
Problems that might occur
After my first try I had this quite discouraging problem. The fork oil was leaking through the seam between the drop out and the outer leg tube. Bummer!
My solution to this was a vacuum pump and some very high viscosity glue (spell: superglue) Some rubber to seal the upper hole, the wiper seal down below luckily fit my pumps inlet. I used some sticky tape to prevent the glue from ruining the carbon finish. Then applied a few drips to the seam and watched the glue slowly disappear to the inside. 3 drops of glue seemed to be enough. A few hours later the glue had hardened. no more leaking oil. Phew!
My second problem was the wiper seals. On one side I had the oil coming past very fast. I was not able to find a source for new wiper seals. And I had the feeling that those original seals would not be up for the job anyhow as they were meant to keep the dirt out, not oil in. My first thought was to use the seals that fit the Hydracoil Judys (and the 28mm SID btw) but the outer diameter was very different.
So I tried these: BASL 28x35x5mm rotary seals. BASL is the German identifier for a rotary seal with retaining spring and an extra dust lip. It might be ok to use a seal without that lip to reduce friction. But I did not want to use those ugly fork boots...
This is what it looks like. The spring should point to the inside, as long as you use the version with a dust lip. If you press it all the way in, it look like in the picture. Sooo much space left for dirt to stack. No good. Would be better to press it in so it sits even with the upper edge if the aluminium.
But for me, this is the better option. Press the new seal all the was in. And fit the old original seal on top. Gives a little bit of extra protection. Plus looks all original.
Conclusion
By doing this conversion, imho, you gain on the function and durability side. The open oil bath works better and has less friction than the old dampening cartridge. There is only one seal as opposed to the 3 on the old version.
The bushings are basically swimming in oil so no grease problems to expect.
The steel springs will work no matter the outside temperature and will not harden over time as the old elastomeres did.
On the down side I can only see one: weight. The springs and the oil add quite a bit.
The other option would be a Eglund total air conversion. But those are very hard to come by these days. And they are not as problem free as the hydracoil version. If you loose air you will have to cope with a totally collapsed fork. With the steel springs worst thing to happen is loosing too much oil. But then its only loosing the dampening. The height wont change. Riding a bit slower you would be able to finish you week traversing the alps anyhow ;)
