Why can I not reinstall a drain linkage assembly for my bathtub?

Question

I have a bathtub where I discovered that the prior owner had lost the linkage assembly plunger down the drain, but screwed the broken overflow cover plate back in place. With a new overflow cover I went to reinstall the linkage assembly, but the section of the assembly with the cotter pin is getting stuck on the lip of the overflow drain pipe and not able to move further down. If I try to force the assembly down into the pipe, the linkage assembly hooks pop apart, resulting in the plunger down into the bottom of the pipe.

What am I doing wrong when trying to reinstall this?

Answer 1

1. Likely, part of the original linkage is still stuck inside. Hopefully, it can be fished out with a bent wire or a pickup tool (claw grabber), such as that below. (Magnetic tools likely would not work, since parts are probably brass.) An illuminated inspection camera (endoscope) might give a view inside, if needed.

_{Image from Amazon}

2. If the cotter pin itself is hitting something, the long end can be ground shorter.