the mystery of the missing clutch fluid

My buddy and I went riding today. Me on my 450SX and him on his 450EXC. About 2 hours into the ride his clutch goes south. It breaks down like this. I am on a steep and extremely muddy hill and stall my bike while trying to turn hard right to get on a different trail. My buddy has to come to a stop and when he starts up again the clutch feels funny. By the time we got to the top of the hill all of his fluid was gone (we checked and it was bone dry). We limped back to the cars and when he got home he couldn't see any damage to the lines, the master or slave cylinders. We didn't have any fluid to pour back in to see if there were any leaks. He did just finish putting on the slave cylinder protector and he bleed the clutch during that process. But it was fine for several days and several hours worth of riding. Any ideas? :)

I would check the slave cylinder.I know of a few that have leaked.

Also check the crimp connection on the clutch line near the MC. A few of those have been reported to leak at the crimp.

If you are sure there is no fluid anywhere on the bike and the clutch worked fine before, then the fluid could possibly have leaked into the gearbox, past the slave cylinder seals,... and been absorbed by the engine oil.

By the way, there is no need to bleed the slave cylinder when fitting the clutch guard, as long as the clutch is not pulled while the slave cylinder bolts are removed, the piston will seal the oil in, exactly the same as a disc brake caliper.

Once again this board amazes me. I was just out washing my 520 EXC. While wheeling it out onto the drive, I noticed a tiny stain on the garage floor from under the bike. It looked like oil, but not dark like motor oil. Hmmm I thought. I swiped my finger in it, and it was oil, but it didn't make sense to me since it was so clean, until later, it dawned on me that it must be the mineral oil from the clutch line.

Before my last ride I had put in all new clutch fluid, and now I think its leaking (slowly). The clutch feels a little weird too, harder to pull.

Now I come in here to see what's new on TT, and sure enough there's a thread on leaking clutch fluid! :)

I'll have to get out there and take a closer look at it next chance I get. -Ed

It turns out that it was the crimp on the hose near the master cylinder. It was a bad crimp and leaked when the clutch was pulled in. Good call JEB!

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