Detroit Report‥ DISK BRAKES will completely replace drum brakes in most American cars by 1971. Disks will be the standard front-wheel brake on all but a few－odd models. Ford has led tbe way. They've been fitting disks on all cars ordered with power brakes since last year. For '69, Chrysler is expected to do tbe same, and some GM models will follow, among them the GTO, the 4-4-2, the Skylark GS, and the Chevelle SS.