Westinghouse is a good example. I did some subcontracted work for part of the old Westinghouse company several years back
http://en.wikipedia.org/wiki/Westinghouse_Rail_Systems
...now all subsumed into Siemens..
Only part ended up in Siemens. They gradually sold off all their businesses except for "Group W Westinghouse Broadcasting" when they took over or merged with CBS and or Viacom. (they changed the names of the pieces a few times)
http://en.wikipedia.org/wiki/Westinghouse_Broadcasting (see the section called "merger with CBS" and "Epilog"
Actually I understand that Westinghouse Air Brake was almost always a separate company almost from the beginning. http://en.wikipedia.org/wiki/Westinghouse_Air_Brake_Company

