Ok kiddies -- I've been on this rock almost 75 years and here is a 2-speed rear end story. Back in the day my uncle had a 57 Stud Golden Hawk with a Caddy engine and a Columbia 2-speed rear. I remember getting in that ride and him and he would shift the rear end at about 90 MPH ... how fast we went from there is hard tellin' ... but what a ride.