Any idea what would cause clutch fluid to turn black (like oil. Really dark.) within a couple hundred miles after changing it? The bike has steel braided lines, and I know the fluid will turn dark if it gets mixed with air or water over time, but I don't think that's happening. Everything is tight from what I see. I haven't checked the clutch plates, but it shifts fine. This has happened over the last 5-10k miles actually. I swap it, and it goes black again within a couple tanks of gas.
The bike is a non-VFR, but that shouldn't matter really.
Thoughts on where to start looking?
Sounds like the brake fluid you are using (assume dot 4) is not happy with some of the "rubber" materials.
It's a simple system so either the master cylinder piston seal, the hose, or the slave cylinder O-ring. I'd guess one of the elastomers is getting soft & deteriorating. It's definitely worth a look.
Possibly someone used an incorrect fluid in the past and that caused softening.
i would say the slave cylinder and or master need a rebuild. for what its worth, my fluid is doing the same thing right now.
I put a master cyclinder rebuild kit in it a couple thousand miles ago. Honed the bore as well. Did not do the slave cylinder though. Mabye that's up next. Good ideas.
Looked up my slave cylinder parts. Should I only replace the rubber seal, or should I do the spring (not sure how that would cause an issue with the fluid being dark) and the piston/cup as well?
Fwiw, my VTR1000F did this within weeks of buying it new. Never did figure out the cause but it certainly was due to wear or age.
Did you do anything to track it down? Or live with it?
I am thinking calipers.
Since we don't know the are or model of the bike, we just have to guess.
The calipers is were the heat is created.
If there is moisture in the lines the heat and moisture will start to eat away the aluminum.
Oh...the bike is a ZX10 Ninja. Eat away the AL? I don't have any AL eaten away anywhere....
Really?
So you have had the calipers taken a part and the insides were shiny and new?
I find that odd.
Brake fluid is an extremely harsh chemical.