I found an article on another forum. It was published in the April 1949 edition of Popular Science magazine. I found it to be the best explanation of the operation of the Borg Warner overdrive unit that I have encountered. It probably won't be news to some but might be helpful for others. Unfortunately, the actual article is too large to attach so, if interested you can access it by this link and then searching "How overdrive works" in the search this issue box.
https://books.google.com/books/about...d=eSQDAAAAMBAJ