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Piggyback non-emulsion shox, worthwhile customizing forks to oil/piston/nitro setup?

Chuck78

Chuck78

Forum Sage
Past Site Supporter
I have just recently acquired a rebuildable set of really good Fox Factory Shocks with the piggyback reservoir and a floating piston that separates the oil from the nitrogen charge to avoid foaming of the oil typical in emulsion type shocks that most of us probably run, as the cavitation or foaming changes the dampening characteristics after hitting a lot of bumps.

It got me wondering...Now if I only had true cartridge forks... I just had a brainstorming idea on how to convert our standard emulsion forks with emulators into the DeCarbon style floating piston nitro forks...! Maybe that is overkill, but I do have a very affordable machinist friend locally and another across the state who rides a GS... Maybe next year I will make a prototype for my bike, see if there is any interest, and have him make some up for 35mm and 37mm forks!

With some shorter Sonic Springs, I see it being pretty basic to make up an aluminum bore that sits between the emulator and the spring, with a floating piston inside of it. The only tricky part would be machining in an install/bleeder passage and countersunk bleeder bolt.

What are the opinions on converting our old GS forks over to emulators with a non-emulsion setup? More consistent dampening to match the rear seems a given, compared to trying to swap in a much shorter height modern fork and being forced to swap wheels and brakes and do some head bearing retrofits.


Thoughts?????
 
This mod would require machining an aluminum tube the I.d. of the forks that sits on the emulator as the springs would, with a wider ledge for the spring to sit on and a catch lip so the piston doesn't ever come out the top, and an aluminum piston to go inside the first tube. Machine two o-ring grooves in the piston and two in the top outside portion of cylinder/sleeve. The big drawback is filling the fork legs with oil,
The volume of air space above bottomed out piston should be equal or SLIGHTLY GREATER than the amount of fluid that the fork legs displace as they reach full bottom out travel. Easy to calculate by measuring oil level extended with no spring, then fully compressed, then doing some volumetric calculations for cylindrical shapes...

An improvement on the design would be to make the sleeve thick enough to drill a tiny bleed passage through it's wall to the area below the o-rings, then machine a slight slot on the outside that is connected to the hole at the top, then at the bottom limit of the piston travel, drill a hole through the sidewall from the groove to the exact spot where the piston will be at it's lowest. Then at the top, you have a recessed/countersunk hole with a short allen head screw and o-ring or copper crush washer that plugs the bleed passage. Steel allen not s.s. so you can use a magnetic allen driver. the inside bore should have an internal snap ring groove or at the very least three locktited set screws that keep the piston from going all the way down, and provide a stop for it when pushing out the extra fluid and air.
You would basically overfill it, install the assembly without the bleeder screw, push it down with a dowell rod to seat it against the cartridge emulator valve, then with a second dowell, push the piston down slowly while holding the outer tube against the emulator, and watch the air and excess oil bleed out (with forks still fully extended). Then install allen screw with o-ring or crush washer... The bleeder passage doubles the machine work, but seems pretty crucial to an easier install...

May be a winter 2014-2015 project collaboration with my machinist friend if I ever run out of projects!
 
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