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Was bleeding clutch fluid the other day and noticed that there was a very thin and brittle layer of brown substance kn the floor of the reservoir. When disturbed it would break away in brittle sheets. I did my best to suck it up with a syringe but I'm just wondering what would have caused it?

Hydralic fluid is hygroscopic so absorbs water and anything in the water into the fluid. That gunk is years and years of mineral crap taken from the air etc. if you've disturbed it I'd consider replacing the reservoir or the entire master. Cheap part and better to have done that than to allow some gunk to block or restrict the lines and/or slave.

If it's black then it's normally a sign of aging seals in the master or slave cylinders or rubber in the flexible lines. Basically as the seals get older the rubber gets harder and weaker. The action of rubbing the seals against the cylinder walls strips off a tiny bit of rubber each time as a superfine powder which slowly makes its way up to the fluid reservoir. So when you start getting black in the reservoir you should replace the seals and check the lines for perishing.

Brown I don't know about though - could be rust except that I can't think of any steel anywhere in the clutch system.

Probably as above minerals or bits of the slave cylinder boot.

I replaced the master with an OEM, slave with an aftermarket unit, and replaced the factory rubber line with a braided line.

After a fresh bleed I had bits of black sediment in the clutch master. Fluids also turned a little bit dark from the clear yellow.

Seems to be normal.

Thanks for all the suggestions. Clutch seems to be working fine, rubber line was replaced with braided a while back. Can't remember if it was there then or not

mitch_f1 wrote:rubber line was replaced with braided a while back.

from China?

949 racing so whatever they use.

shoud be good then.