I have an older house, with the hot, cold knobs and middle diverter. I have changed both the hot and cold sides with no problem. I have taken the packing screw, cap, the small nutt, the larger nutt, the screw on cover that conceals the stem, now I only have the stem left but it will not come out. There is a brass piece that will turn and seems to have threads but will not come out? I can not get the rest of the stem through the opening without taking off that brass piece? Any suggestions, this has turned into an all day affair. Please help.

I have an older house, with the hot, cold knobs and middle diverter. I have changed both the hot and cold sides with no problem. I have taken the packing screw, cap, the small nutt, the larger nutt, the screw on cover that conceals the stem, now I only have the stem left but it will not come out. There is a brass piece that will turn and seems to have threads but will not come out? I can not get the rest of the stem through the opening without taking off that brass piece? any suggestions, this has turned into an all day affair. Please help.

Does your valve look like this? See image. Let me know. Tom