fox air bump help

[karatejosh]

Hi guys need a little help just got air bumps on my rig but one of them has no oil in it due to the shradder valve getting messed up in shipping. So i just drained them all (2 of them are used anyway) to make sure everything was even. I have two questions 1. after looking at the diagram and reading the bellavista info i see no reason a cant just fill it with oil through the shradder valve but i wanted to ask to be sure it dose not appear to make any difference if the bump is extended or closed but i would like some advice to be sure? Question 2. i know factory is 5wt i happen to have a bunch of good maxis 7wt oil from my race bike shocks i know you can run it but my question is will it really make any noticeable difference? For reference i have a 2700 pound Toyota buggy and i dont race the bumps are all 2 inch. here is a picture of my buggy.

 

[Fabrik8]

• It's an emulsion unit, so filling through the Schrader valve is no problem. Same reason you can drain it through the Schrader valve. You can take the entire valve off the body instead of filling through the valve core hole though.

• Doesn't matter if it's extended or compressed when filling, there will be less oil than there is cavity volume regardless. Unless you overfill it, then you risk hydrolocking it under travel. Bad.

• You'll want to loosen the valve core and slowly compress it fully before pressurizing with nitrogen, so the shaft volume will force more of the atmospheric air out of the Schrader valve (which will be replaced with pure nitrogen during pressure fill). That's optional, but good to do. It will automatically re-extend during filling, obviously.

• If you're changing spacers or valving or whatever, you can fill the body with oil before reinserting the shaft/piston stack into the body. That's the way the factory assembles them.

• Changing fluid weight will change the damping. You'll only notice it when the bumps are functioning.

• If you want to keep the factory damping, use the factory fluid weight.

They're really no different than an emulsion damper or emulsion coilover. Any advice you find for those (filling, tuning, whatever) will generally be good for the bumps as well.

 

[Fabrik8]

BTW, the buggy is sweeeeeet. So clean and simple.

 

[karatejosh]

Ok im overthinking it which i tend to do sounds like im on the right track and thanks i cant claim any of the cool work its all chris at marsfabs dooing

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[Fabrik8]

Ok im overthinking it which i tend to do sounds like im on the right track

It's only overthinking it until you do it the first time, then it becomes straightforward and intuitive. I'm a professional overthinker (engineer).

 

[Fabrik8]

Here's something I just found about complete disassembly/reassembly from Fox:

http://www.ridefox.com/fox_tech_center/owners_manuals/EMULSION_REBUILD.PDF

http://www.ridefox.com/dl/offroad/FOX_OR_BumpStop_Exploded_A.pdf

The second one will give you a good visual, maybe.

 

[Mac5005]

Just put the fox spec volume amount. I doubt you will ever notice the difference in valving between 5w vs 7w as the time it's compressing the bumps is so minimal.

 

[karatejosh]

Ok so this brings up another question i was told 100cc for my 2 inch bumps and 125 for my 4 inch bumps that i put a spacer in to make thr 2 inch the info above seems to state 125cc for both but the 4 inch bumps so have a longer body so it wouls make sence to have more fluid

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[Fabrik8]

the info above seems to state 125cc for both but the 4 inch bumps so have a longer body so it would make sense to have more fluid

No, it's just badly listed in the chart. In the chart it's a Fox 2.0 bump with 4.0 inch travel, there is no mention of the 2.0 bump with 2 inch travel in the Fox document.

I am seeing some discrepancy about that though, some vendor sites list the 2 and 2.5 inch travel with 100mL, and the 3 and 4 inch travel with 125mL, and some sites list everything but the 2 inch travel as having 125mL.
Not a big deal, but you'll be changing the spring rate for any given nitrogen charge pressure because the nitrogen volume will be different. That's a way to tune spring rate too obviously.

If you're worried about the spacer and want to keep the volume of oil the same on the 4 inch travel units, you can remove the spacer and put it in whatever container thingy you're using to measure the oil (before adding the oil to the container). Then the spacer will displace the oil and the volume will be automatically subtracted, etc. That won't work if you're just using a syringe for measurement.

 

[karatejosh]

10 4 thanks guys sounds like im still on track i have a ratio rite and a syringe but im not really woried about the spacer volume im not that bad ass lol

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[Mac5005]

My chart shows 125cc for 3 & 4" travel 2.0s. I wouldn't worry about the spacer taking up too much volume, if anything it will help to get the spring rate up at compression.