brake systems
It still amazes me that the industry had to be FORCED to apply a simple engineering change so late as 1967 to make brakes so much safer. To their credit, Cadillac was ahead of its time with dual master cylinders in 1960, but why only Cadillac? Then AMC followed in 1962. But before that, with the exceptionof one other make, a failure of one component left you literally careening toward disaster. The only other carmaker to address the issue before Cadillac was Hudson, who retained a backup mechanical system that would kick in if the hydraulic system failed. I've never seen how it was engineered, but sure would like to.