To install the new diaphragm assembly, insert the assembly into the body, and using hand pressure, compress the spring while looking inside the body thru the arm hole. You should see the top of the pull rod sticking thru the seal and into the pump. Slide the arm in and hook it onto the rod. Make sure the arm isn't in there upside down. (been there, done that) After it is seated on the pull rod you can release the pressure off of the diaphragm. Now you can line up the holes in the arm with the holes in the body so the pin can slide in. Done.