I don't know if this will help but here is a link to the parts list and repair instructions for the 5850-0001.
http://www.xylemflowcontrol.com/file...43000-0202.pdf
Is the cam touching the wear plate at the back? It should and the other end of the cam should be flush with the front surface of the pump. If the cam is protruding from the front and touching the wear plate, maybe the wear plate isn't seated correctly.