Cannot screw in the brake caliper piston

[musubk]

I took apart a set of EA82 front calipers today, to replace the seals inside the cylinders. One of them I'm having trouble getting back together. On the 'inside' of the piston, there's a female threaded hole that should screw onto a threaded rod inside the caliper. My problem is that female threaded hole in the piston spins freely within the piston. That bit, which seems to be set into a thin rectangular plate that connects to the outer piston body, doesn't seem to be retained in that rectangular plate at all. I can't screw it onto the rod in the caliper because, after a couple of threads engage and I get some resistance, the outer body of the piston just spins forever without turning the hole about the threaded rod in the center.

 

I hope this description is making sense. The threaded hole inside the piston just spins freely when turned clockwise to install, but is retained when spinning counterclockwise - which allowed me to unscrew the piston from the caliper but not reinstall it. Is it supposed to do this, or is the retention of that part somehow broken and I need a new piston? I feel like I may be missing something simple. The piston on the other caliper screwed back in with no trouble other than being very difficult to turn.

[two85s]

Sorry I can't be of more direct help but this video may give you some tips.  There are more you can search or look it up in a FSM.  Good luck.