Diagnois my clutch problem on 1991 Ford Explorer

I was driving my 1991 Ford Explorer XLT when I pressed the clutch in to shift into 5th gear it went to floor and it lost all pressure to it. After that I could not use the clutch to shift at all. What's the problem?

Asked by for the 1991 Ford Explorer
Check your clutch fluid, is it up to the correct level? If not, then you may have a problem with your clutch hydraulics. If so, I advise doing BOTH the Master and the slave cylinder as a set, which will mean removing your transmission an doing a clutch job. You need to remove the transmission to replace the clutch slave cylinder. If you do a clutch job, be SURE to replace the clutch slave as well, this is a must.
here are some shops:
Fluid levels are correct. What's the differnce between the slave cylinder and the master cylinder and are they sold seperately or together?
They are sold separately. The slave cylinder is the functional mechanical part inside the bellhousing of the transmission that actuates the clutch. The master cylinder supplies the fluid and is under the hood near the brake master cylinder.

I have personally never had issue with the clutch master cylinder, but have experienced multiple repetitive failures of the slave cylinder on the M5OD Mazda 5 speed manual transmission in the Explorer, Ranger, Aerostar, F150.
1 more answer
To support Dan, the slave cylinders are very common for failures on these. It is an assembly containing the throwout bearing as well inside the bellhousing of the transmission (thus requiring removal as Dan mentioned).