Cam an Follower Problem

I am trying to make a mechanical computer in Blender. The computer is going to involve grooved cams with pins as followers. The best way to rig it seemed to be using a transform constraint which converts z-axis rotation into y-axis movement. It works well except when the cam turns 180+ degrees. At the 180 degree mark the follower jumps to the opposite limit of travel instead of continuing on. I have included the .blend so you can see what I’m talking about


Constant Lead Cam.blend (175 KB)