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Formerly PaintPeelinPbody
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Discussion Starter · #1 ·
So I've got a 2017 Fox 34 with a non-EVOL air shaft set at 150mm. Not sure if this is NA or NA2. I'm sure my

I also have a 2018 Fox 34 130mm EVOL air shaft.

I was thinking of swapping the parts around to make the EVOL air shaft my 150mm travel.

While I'm at it, I could also fiddle with somehow increasing the negative volume of the air shaft as well.

Text Woodwind instrument Reed instrument Wind instrument Rocket



Could you move the black top out bumpers to make for more negative volume?
 

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Yes you can swap the parts and leave out the top out bumper, just be careful to inflate it slowly to keep the negative chamber inflated so the top out isn't too harsh but after that it should be fine
 

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Formerly PaintPeelinPbody
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Discussion Starter · #3 ·
I don't want to lower the volume, I want to increase it. Wouldn't that mean stacking top out bumpers?
 

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Formerly PaintPeelinPbody
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Discussion Starter · #5 ·
So, that white piece/piston, that's what determines the volume of the negative chamber?

If, for example, you shaved down that piston to be smaller, you could effective increase the negative chamber volume, right?

Why does Vorspung used a hollow expanded piston in the Luftkappe, vs just modifying these parts on the air spring?
 

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the position of the piston inside the stanchion is fixed around how far the equalization dimple is from the end (ie the 72mm on your drawing)

Luftkappes generally remove as much space on the negative side as well as the hollow chamber to take some volume from the positive side. For example an NA2 luftkappe (shaft on the right) has a hollow dome PLUS a smaller neg. plate (the silver tube) to be more like the EVOL size on the left.

*36 Evol can't have the topout bumper removed though
 

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Formerly PaintPeelinPbody
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Discussion Starter · #9 ·
Ok, just so I follow:

The equalization port is at 72mm from the bottom of the stanchion.

If I remove the top out bumpers, the piston will sit below the equalization port. I would assume this would make setting sag difficult, because on the first compression, you'll equalize the chambers and now sag will be different.

So ideally, you'd want a material stiff enough to resist compression of the positive chamber to keep the piston at roughly 72mm, but also provide some top out comfort.

What happens when removing the top out bumpers? It looks like Vorsprung does this on some of the kits.

Per their directions, it's just a matter of compressing the fork a few times to get the chambers to equalize and living with pneumatic top out.
 

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Formerly PaintPeelinPbody
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Discussion Starter · #13 ·
It's not about it adding negative volume, it's about the inability for the negative volume to be used as a pneumatic top out bumper. With a hole there, I'm guessing that's a no.
 

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Ok, so it basically boils down to whether the rhythm air spring uses the inside of the air shaft for negative volume?
No, they all do that (the transfer port is under the piston) the hole is a remnant from the original top out o-ring stop. If you remove the top out bumper from an air shaft like this, when you inflate the fork the hole gets pushed to outside the sealhead and all the air blows in to your lowers :)
 
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