If you have a later Model B, lets say a 55, the picture does not have the aluminum ball 37.
Here is a link
http://chevy.tocmp.com/1955truck2shop/55ctsm06m06.htm So if I read it right, the large steel ball, 3/16, goes in the pump discharge cavity with the bronze spring and the other steel ball goes in the main well support for the power piston.
The aluminum ball must be for the earlier model B only.
Well I know what I'll be doing tomorrow. My air horn is coming off because I have the later model B, and I put the aluminum ball in the main well for the power piston. I guess it makes a difference.
