Hitting the Brakes: A History of Automotive Brakes - Page 2
Other car manufacturers followed suit. In 1924, the Hupmobile Straight-8 came with four-wheel hydraulic brakes, while the Six still had mechanical brakes. Stutz, in 1926, was using hydrostatic brakes with six bladders replacing brake shoes, a system that lasted only a year before Stutz licensed Lockheed hydraulic brakes. The hydrostatic brakes worked OK but the water in the system froze up during cold winters. There were definite advantages to the hydraulic brakes but few manufacturers—among them Dodge, Desoto, Auburn, Graham, and Plymouth—were using them by 1931.
But GM and Ford still utilized mechanical brakes. It wasn't until the mid-30s, in fact, that GM went to Bendix hydraulic brakes. Vincent Bendix, after meeting French engineer Henri Perrot at a European auto show in 1924, acquired the license to make mechanical shoe-brakes and took over Perrot's contract to supply brakes to GM. With design improvements, Bendix offered a four-wheel drive mechanical braking system but contention was sharp as to whether mechanical or hydraulic brakes were better. Bendix, figuring no one needed fluids leaking out onto the garage floor, favored reliable mechanical brakes. Lockheed, however, claimed that hydraulics meant less skidding and were, overall, much safer than mechanical brakes. As more manufacturers chose hydraulic brakes over mechanical ones, Bendix eventually purchased Lockheed's Hydraulic Brake co. in 1930, and in the mid-30's GM switched to hydraulic brakes for all its cars.
When the Ford Model A was being designed, Edsel Ford equipped them with hydraulics. When his father Henry Ford test drove one, however, the luck of the draw applied. He got a car that had been tested previously and had a cracked line—so the brakes didn't hold. Hydraulic brakes were out at Ford—at least until the late 30's.
While Ford acknowledged there was a need for brakes, he didn't think there was a need for anything fancy. The Model T, which arrived in 1908, had service brakes applied to a drum inside the transmission—and Ford used these mechanical brakes through 1938. Ford was, in fact, the last auto manufacturer to switch to hydraulics.
Brake Assist (Power Brakes)
Some early innovations with brakes now seem way ahead of their times. Brake assist, for instance, was first made available in 1903 with the Chicago-based Tincher. A small pump compressed air to stop the car, or, if you wanted, the same pump could inflate the tires or toot the whistle. The 1928 Pierce-Arrow was the first production car, however, to come with a vacuum-operated power booster for brakes, the Bragg-Kliesrath. Caleb Bragg and Victor Kliesrath, in the mid-20's, had invented the vacuum-assisted brake booster for the aeronautics industry. The intake manifold supplied the vacuum needed to reduce the amount of effort required to apply the brakes. Chandler cars, from 1927-29, came with a Westinghouse Vacuum Booster, and by the early 30s, Lincoln, Cadillac, Duesenberg, Stutz, and Mercedes were also including vacuum- assisted drum brakes. Drum brakes remained standard, however, because they worked well and were cheaper to manufacture than disc brakes.
Beginning in the 40s other power-assist systems began to appear, and by the 50's power brakes were common. Systems such as the Hydrovac, the Hydroboost, and the Treadle-Vac (known as the Easamatic on '52-'56 Packards) came factory-installed. In the Hydrovac system, when the driver pressed the brake pedal, fluid pressure was increased to a slave cylinder and the wheel cylinders. More pressure activated a valve that, in turn, activated a triangular arm. The arm rotated valves to close an atmospheric valve and open a vacuum valve, pulling vacuum air into a large chamber and pushing a bellows against a valve in the slave cylinder to increase fluid pressure to the wheels. It was a real Rube Goldberg system but it worked.
The Hydroboost system, rather than using a vacuum, relied on power generated by the power steering pump. The Bendix power booster was the Treadle-Vac, mounted on the floorboard right under the brake pedal and available on all GM cars in the 50s as well as on Edsel, Lincoln, Mercury, Hudson, Nash, and Mercedes models. The Treadle-Vac was a single line system, however, which meant that a failure of any hose or joint could impair the entire system. In 1959, the Delco-Moraine power booster mounted high on the firewall became the system of choice instead. All these systems meant that the driver no longer need stand on the brakes to stop the car. With far less pressure, the car could be brought to a halt.
There were also early self-adjusting brakes. The 1925 Cole, in its last year of production, had them. They would not appear again until 1946 when Studebaker used a Wagner Electric Co. mechanism. As the linings wore down, a pin and lever moved against a tension spring, engaging the adjusting wedge which moved the linings slightly and kept them at the same distance from the drums. Self-adjusting brakes showed up on the '57 Mercury and the '58 Edsel and were recommended to purchasers anxious to avoid frequent and costly brake adjustments. By the mid-60s, AMC was offering self-adjusting brakes, as well.
Antilock (antiskid) brakes (ABS) are not entirely new, either. They are a safety feature which prevents the wheels from locking while braking. If speed sensors detect that a wheel is about to lock up, a series of hydraulic valves reduces braking on that wheel, preventing a car from going into a spin. Gabriel Voisin, a French pioneer in aeronautical and automotive engineering, introduced them in 1929 for airplanes. By 1936, Bosch and Mercedes-Benz had an electronic ABS for the Mercedes. It wasn't until 1958, however, that a practical ABS was developed for cars: Maxaret was developed in Great Britain and used in the Jensen FF sports sedan in 1966. The Ford Zodiac in the 60's experimented with ABS for all-wheel drive but the ABS was very expensive to produce. Then, in 1969, Ford brought out the Lincoln Continental Mark III and the Thunderbird with "Sure-Track", a Kelsey-Hayes Auto-Linear antilock unit in which wheel sensors transmitted data to a transistorized computer set behind the glove box. The system controlled only the rear wheels, there were some technical problems with the system and, again, the production costs were very high.
In 1971, Chrysler introduced the first reliable ABS with its Bendix "Sure Brake" system on the Chrysler Imperial. That same year, GM offered an ABS "Trackmaster" as an option on its rear-wheel drive Cadillacs. Ford stayed the course and, in 1975, included its "Sure Trak" on the Lincoln Continental Mark II and the LTD station wagon. In the 80's, Ford also had an electronic, 4-channel ABS on the Lincoln Continental Mark VII (1984) and utilized a Kelsey-Hayes rear-wheel ABS on its F series trucks (1987).