Just to add some info, parts for these are hard to find. When I rebuilt mine the spring was broken and the boot was torn. I ended up buying parts here, it's a jeep parts place but some jeeps used the same coupling as GM.
Also, pressing that dowel pin out and then back in is a bear!
Hope this helps, Rg
http://www.quadratec.com/products/918018_02.htm
or complete coupling
http://www.quadratec.com/products/918018_06.htm