I am restoring my 67 Malibu and began looking at the rear springs. I noted that I was missing the rubber insulator at the top. I also noted that installed at the top was somethng that looked like an inverted dish, about 6" diamter, inside the spring. There is a bolt going thru it with a nut used to hold the "dish" tight against the top of the spring and the frame. None of my manuals show what this is. After I install the new springs and insulator, do i still need to re-install the 'dish" and bolt, or does the spring stay in place alone? Does anyone know what this is? thanks