Fox Brain rear shock - oil from the air valve?

[scottm]

I found the rear shock valve cap cracked, and the threads corroded, so I decided to remove the aluminum valve to clean the threads. When I depressurized, green oil came out, maybe a thimble-full, not much. But nasty. Is there supposed to be oil in there, and if so, is it bad that I let it out?

 

[ravewoofer]

Scott, that shock is most definitely oil based. The Brain Shock is used to provide a firm platform for the rear end. It's basically a heavy mass that holds everything firm. A decent sized bump will force the oil quickly and raise the mass so as to let the shock blow off and go into its movement. Part of the shock's adjustability may be air based (it's hard to see if there is a schrader valve there) for sag, but the mass works with oil.

I doubt a bit of oil will make much difference, but oil is needed to make the Brain shock perform.

 

[scottm]

Thanks, yes it's an air spring, oil damped, and I suppose metal springs on the mass with dampers. I looked at my manual, after cleaning you're supposed to leave just a little pool of oil above the O-rings as a reservoir, but that's not the internal pressurized area. If that's their philosophy, maybe they leave a little in the pressurized piston as well. Might be better to depressurize with the valve up next time I guess.

This has been an awesome little shock, survived a bunch of Michigan Winters now, and it was still right on pressure when I finally checked it last week.

 

[S&S1stCruzer]

When mine did that I sent it back to specialized/fox to get it maintenance.

 

[scottm]

When mine did that I sent it back to specialized/fox to get it maintenance.

Was that the only problem, or were there other symptoms? Mine is working fine, just needed some pressure added for the first time in years. If I hadn't wanted to take the valve off and clean the threads, I wouldn't have let any air out and wouldn't have noticed. I'm thinking they left a little oil in the cylinder to keep the seals lubed, and I got that out. If I'd done this with the bike upside down it might have kept the oil in.

 

[S&S1stCruzer]

Was that the only problem, or were there other symptoms? Mine is working fine, just needed some pressure added for the first time in years. If I hadn't wanted to take the valve off and clean the threads, I wouldn't have let any air out and wouldn't have noticed. I'm thinking they left a little oil in the cylinder to keep the seals lubed, and I got that out. If I'd done this with the bike upside down it might have kept the oil in.

Maybe i didn't read your thread right, but what happened to me was the actual brain adjustment knob seize up and I forced it, so air and fluid came out. I called my LBS and they sent it in for me.

 

[scottm]

Maybe i didn't read your thread right, but what happened to me was the actual brain adjustment knob seize up and I forced it, so air and fluid came out. I called my LBS and they sent it in for me.

Oh, not the same. The air fill valve on mine had a cracked cap, so the threads got corroded. I turned the fill valve out and cleaned it, put a new Shraeder cap on it. The oil came out when I let the air out of the valve.

 

[Ozdunc]

Scott,

I wouldn't worry to much about it. Its just a small amount of oil to lube the rings between the positive and negative air chambers.


Re-pressurise the shock as you would normally. If it rides OK - sweet. If it loses air, you'll probably need to change the seals.

The seals are readily available from Fox, and its a fairly simple job if you are mechanically minded and have a bench vice.

Cheers

 

[scottm]

Thanks, that's pretty much what I assumed. There should be a little oil left in there, probably enough. If it's been sitting I should probably flip the bike over to distribute the oil over the seals before I ride, just to be extra anal about it.

 

[Ozdunc]

Good idea. It will also lube the fork foam rings and seals as well.