I opened up a 1981 Campy Grand Sport read hub to change the bearings and replace the grease and discovered a bad cone. I wasn't able to find a replacement GS cone but was able to find Record cones. Problem is, that the GS and Record cones have a different profile and use different size bearings.
The GS cone is more shallow and uses a smaller bearing.
The Record cone is more concave and uses a bigger bearing.
I did a lot of internet and forum searching to see if swapping was possible, but found no definitive answer.
So I used the Record cones and larger bearings but left the original cups in the GS hubs.
Problem is, I can now hear the bearings slapping into each other. I believe I have the bearings adjusted correctly.
No play with skewer tightened and wheel spins freely: a little play with skewer loose.
Anyone have some knowledge on this?
PS. I also thought to title this: Trouble with my balls slapping. :-)