This is from Wikipedia - and they started on cars earlier then I thought:

"Modern-style disc brakes first appeared on the low-volume Crosley Hotshot in 1949, although they had to be discontinued in 1950 due to design problems.[1] Chrysler's Imperial also offered a type of disc brake from 1949 through 1953, though in this instance they were enclosed with dual internal-expanding, full-circle pressure plates. Reliable modern disc brakes were developed in the UK by Dunlop and first appeared in 1953 on the Jaguar C-Type racing car. The Citroën DS of 1955, with powered inboard front disc brakes, and the 1956 Triumph TR3 were the first European production cars to feature modern disc brakes.[2] The first production car to feature disc brakes at all 4 corners was the Austin-Healey 100S in 1954.[3] The first British company to market a production saloon fitted with disc brakes to all four wheels was Jensen Motors Ltd with the introduction of a Deluxe version of the Jensen 541 with Dunlop disc brakes.[4] The next American production cars to be fitted with disc brakes were the 1963 Studebaker Avanti[5] (optional on other Studebaker models), standard equipment on the 1965 Rambler Marlin (optional on other AMC models), and the 1965 Chevrolet Corvette Stingray (C2). The 1965 Ford Thunderbird came with front disc brakes as standard equipment."

http://en.wikipedia.org/wiki/Disc_brake

The rears on my '31