First thing we need to do is figure out what the problem is. It could be as simple as the return spring is broken. The Imperial Club not only has troubleshooting info, it has a parts manual back near the home page. I have the link to the trouble shooting area attached.
http://www.imperialclub.com/Repair/Transmission/index.htm
http://www.imperialclub.com/Repair/Transmission/index.htm