Clutch update, think I found the problem..., Looking for help on draining/replacing CMC fluid. Options

[Delta_Phoenix]

I've been doing some reading about the problem I'm having with my clutch. I came to the conclusion that since the car will go when started, and the fact that I've had no telltale signs of a bad clutch, that either my master cylinder or slave cylinder needs to be replaced or possibly the system needs to be bled. I haven't replaced my CMC fluid since I've had the car, which is over 4 years now. It just seems odd that this whole thing was so sudden with no signs of an up-and-coming problem. I took off in first, and when I disengaged the clutch to shift, it just wouldn't go. Massive grinding. And now the clutch is stuck engaged and I can only shift with the engine off. Sounds more like a master/slave cylinder problem.

I've also been trying to find some how-to's on replacing the clutch master cylinder fluid, but I came up fairly nil. I know that I have to drain the fluid from the slave cylinder, and that's about it. One how-to said NOT to let the fluid level drop below min. on the reservoir (I completely drained my brake system when bleeding, refilled, and had no adverse effects). But my question is, why not? I'm putting more fluid in it anyway. Is there some consequence to completely draining the system, and then putting more fluid in? It recommended to repeat the process of depressing the clutch, loosening the bleeder valve, tightening the bleeder valve, adding more fluid, rinse and repeat. But why mix old and new fluid? Out with the old, in with the new. I'm rambling. Someone help me out here.

[bindertch]

The only reason why they say to not let the Master cylinder run low is because then you get air bubles in the line. If you are going to replace all of the fluid then you can do this with a vacuum pump. I have drained the master cylinder and replaced the fluid once before in Toyota T100 pickup.