Specialized FSX Future Shock Fork /RS Mag 21 Service

[Elfman]

Here are the innards of my Specialized FSX fork.

Kestrel CSX build

And now for the fork: of course, with a carbon build, I'll need a carbon suspension fork. The early 90's saw a handful of tricked out carbon/Ti versions of suspension forks, and I was able to source a very cheap and good condition Specialized FSX carbon/Ti for this build. I got new decals for...

www.retrobike.co.uk

You can see the stanchion tubes are shorter than Mag 21s are there are no springs on the bottom.

Interestingly, I'm having the same sticking issues that you have, although it has lessened a bit. I think it may have something to do with the alignment of the stanchions when everything is tightened at the crown. I full inflated each leg, secured the fork brace (brake arch), and only then did in slide the legs onto the crown and tighten the crown bolts, even if there was a slight height difference in how much the upper stanchions protruded from the crown. I knew then that the legs would compress on parallel and not be fighting each other at all. Maybe that would help?

 

[BoyBurning]

I had this exact issue with a pair of mine. All worked fine until bolted up, then they went down and stayed there. Nothing would get them back up save for some serious pulling. Took them apart and repeated rebuild several times with increasing frustration and confusion. Then discovered that one of the stanchions was bent slightly at the top where fitting the crown. The legs would compress and rebound fine independently, even with the crown and brace fitted, but as soon as wheel fitted which fixed the lowers all went out of kilt. Only way to solve it is new stanchions in my case but I've given up on them for the time being as it put a real downer on my build and I've not restarted. One plan is to fit some mag21 stanchions and internals in place of the mag20, but I'm not 100% if they will fit / work given the differences, and no one seems to be certain either way. I've got to the point where I don't want to be blowing money on a set of mag21 internals only to find I need mag20 internals and then starting a search again. All pretty frustrating it must be said!

 

[BoyBurning]

What pissed me off most is that I strongly suspect the seller knew about the issue when selling them, but they've sat on the shelf so long in my ownership waiting for the right build that it's much too far in the past for any form of recompense... Grrrr!

 

[Thias]

I had that problem with my fsx staying in the down position. The problem was one of the o-rings being too thick and "sealing" the "upper part" of the fork from the lower part. Kind of hard to describe. The air gets trapped between the stanchion and the lowers but it shouldn't.
It's a decade ago, so I don't remember exactly. But I think it was the lower o-ring that is only there to stop the fork from making a clonking noise when extending all the way. The air needs to be able to pass that o-ring. In my case it acted like a valve.
You can check it by removing the o-ring entirely. If the fork works without it (but makes a clonk at topout) that ring was too thick. The ironic part was, that the old original o-ring did the same, because it was pancaked from old age.