If it goes to the floor with no pressure, chances are the Slave Cylinder is gone, or you are out of fluid and have a leak somewheres. But chances are if you're losing fluid, it is your slave cylinder leaking.
Remember, keep the master cylinder full so you don't suck air into the slave cylinder. Then you put the fluid in the slave cylinder.
The clutch slave cylinder in your 1998 Mitsubishi does not use fluid. The clutch slave cylinder is sealed with grease inside of it.
In the master cylinder
The brake fluid for the entire system is added in the master cylinder container. The slave cylinder does not have its own reservoir.
There are two normal causes. The clutch is worn out or there is a leak in the hydraulic clutch slave or master cylinder. To check the clutch, press the clutch slave cylinder down. If the clutch slave cylinder bellows compresses down to the slave cylinder, the clutch is worn out. Check the clutch master cylinder fluid level. if this is low, then the clutch cylinder need to be checked. To check for a hydraulic leak in the clutch slave cylinder, remove the cylinder's bellows and check for any fluid. If fluid is present, rebuild or replace the cylinder and bleed the system. To check the clutch master cylinder, check the back the of clutch master cylinder for leaks. If fluid is present, replace or rebuild clutch master cylinder and bleed the system. In my experience, hydraulic leaks occur at the clutch slave cylinder.
No, the slave cylinder is a typical hydraulic piston; if the system was 'opened' then the fluid would come out.
All clutch slave cylinder require brake fluid. You will need to check and see if it is Dot3 or Dot4. Do NOT mix the two.
it leaks fluid.
It's the slave cylinder.
Bad clutch slave cylinder or failed soft hose from master to slave cylinder.
Normally Dot 3 or Dot 4 brake fluid.