Started my truck up this morning and put it into reverse, but when I pushed clutch in to put it into 1st the pedal just fell to the floor.

I got it back in my driveway and discovered the clutch master cylinder was dry. I removed the master cylinder and hydraulic line and zip tied it straight along a post in an attempt to bleed out the bubbles. I performed this once before when I replaced my clutch and it worked perfect. This time however, I'm positive I have pushed out all the bubbles, but I'm still able to push in the plunger with minimum force. It is staying full but I'm not seeing any fluid coming out as I push the plunger.

Could it be something faulty with the plunger on the master cylinder?

 

Yes, master's piston seals have failed, replace Master, make sure you get correct year, Ford changed Ranger quick connect fitting in early 1990's, so Master's hose and slave must match connector types

 

What happens when the Pistons in it fail?

 

It doesn't push fluid out it just moves thru the fluid