A real step forward for ABS, however, came when Bosch and Mercedes-Benz developed an updated system for the Mercedes S-Class in 1978. A significant refinement on their original 1936 system, it was a completely electronic, four-wheel, multi-channel system. Other companies soon built on this model and today most cars, regardless of their price class, are fitted with ABS. In 2006, Mercedes unveiled a further update with its Brake Distronic Plus system. Using long-and short-range radar, it can bring the car to a stop even if the driver does not touch the brake pedal—no more rear-end collisions.
Now, back to disc brakes. There were some problems with drum brakes right from the beginning. Heat builds up with them and, over time, the brake can warp, causing vibrations. Disc brakes, on the other hand, wear longer, are self-adjusting and self-cleaning, less prone to grabbing or pulling, and stop better, too.
In 1949, Crosley utilized disc brakes on its Hotshot (though they had to be replaced about once a year) and Chrysler fitted disc brakes on their Town & Country and Imperial models, an innovation which continued through 1954. The Chrysler brakes, built by Auto Specialists Manufacturing Company (Ausco) based on a design by H. L. Lambert, used twin discs that spread apart and rubbed against the interior of a cast-iron drum. These brakes required less pedal pressure than caliper discs and provided more friction surface than drum brakes—but they were expensive to produce. You could order them added to other Chrysler vehicles at a cost of $400 but that was a lot of money back them and few buyers asked for them. Even when they did, they found that they had to exert a good bit of pressure to the brake pedal to bring the car to a stop.-
Bendix made a break-through in brakes in 1962 when it supplied four-wheel disc brakes for the high performance Studebaker Avanti. The introduction was a success—in part because this system assisted the piston in the master cylinder to move, meaning the driver had to exert less pedal pressure. Until then, drivers saw better braking action from drum brakes since they had self-energizing capacity, i.e., the forward motion of the car helped pull the brake shoe into contact with the drum. In 1964, Studebaker introduced disc brakes to all its models and it took only a few years for these improved disc brakes to appear in many other new cars. It was a good thing, too, since the size and horsepower of cars had increased and drum brakes could no longer meet the increased demands.
Throughout the early years, there was a single Master Cylinder reservoir that pumped through a junction block to lines and hoses, distributing fluid to each wheel. The only real problem came if any portion of the system failed or leaked. Then pressure wouldn't build up anywhere within the system—and the brakes stopped working.
In 1960, Wagner Electric (later acquired by Studebaker) developed and filed a patent for a dual-cylinder brake system. Two years later Cadillac introduced a new braking system with a dual master cylinder and separate front and rear hydraulic lines so that if one circuit had a leak, the other could still stop the car—and AMC also offered the tandem cylinders as standard equipment. Studebaker joined them in 1963.
The federal government stepped in, too; in 1967, it mandated the use of dual-braking master cylinders. A 1983 NHTSA report calculated that the feature prevented 40,000 accidents each year.
Automotive companies are experimenting with full contact disc brakes which increase the contact between the surface of rotors and brake pads from 15% to 75%. Siemens has a "green" electronic wedge brake that takes less power, just that of a car's simple 12-volt power system—and achieves a significant reduction in braking distance, not an unimportant feature in emergency conditions. Whatever additional braking improvements are just round the bend, you can bet that braking systems will be more compact and more efficient with faster response times.