confused about this sure-grip

.............OK, just 2 clarify, yes ma mopar made clutch style suregrips from 1957-1964 that did infact act as an open rear as wheels rotated in opposite directions..........only when u loaded it up did the ramps come into effect and lock up both wheels............I have personally had about 10 of these thr u out the years...........and yes I have taken each and every1 apart 4 inspection, and have rebuilt some.....all the discs r flat in the old 1s........newer 1965-69 have a couple beveled discs 2 preload the system........kim...........