Rumplestiltskin

Back in the '50s when I was in high school people used to talk about cars of the past with two speed rear ends. One of my fellow students brought an old Lincoln Zephyr to school that had one. Later I was friends with a fellow who said he'd owned a different make that also sported a two speed rear axle when he was a kid. I have often thought that putting one in a modern car would be fun. Off and on over the years I have tried to find out more info on this topic on the internet and also to see if they are still available somewhere. Up to now I have been completely unsuccessful. Does anyone know which cars had them, and does anyone know if they can still be had?