Imperial Sure-Brake put computer-controlled anti-lock brakes on all four wheels of a 1971 Chrysler Imperial. Bendix developed it, and the option cost $351.50. That was seven years before Mercedes-Benz and Bosch launched the system most people still call the first ABS. Few buyers ticked the box, and Chrysler dropped it after three model years. Yet the basic idea is the one every new car uses today. Sensors watch each wheel, a computer spots a lock-up coming, and the brakes ease off just enough to keep the tires turning. That matters because a locked front wheel can’t steer. Stand on the pedal in a skid with old brakes and the car goes straight, wherever the steering wheel points. The Imperial’s system was built to stop exactly that. How Imperial Sure-Brake worked According to Hagerty’s history of anti-lock brakes, each wheel carried its own speed sensor. Those sensors fed an electronic control box that sat in the trunk. The goal was simple: keep the front wheels from locking so the driver could still steer during a full-force stop. The hardware split the car into three channels. Each front wheel had its own modulator, while the two rear wheels shared a third, Hagerty explains. The modulators were vacuum canisters that worked cutoff and relief valves in the brake lines. Rather than pumping the brakes on and off, the system released pressure in steps as it detected lock-up. A mercury switch also judged how slippery the road was from the rate of deceleration. Then it chose between two pulse speeds, according to Hagerty. Drivers could feel it working, too. In a panic stop, Road Test magazine said, the system clunked “precisely four times a second,” Hagerty reports. Similarly, Jalopnik describes a computer that “rapidly and intermittently released pressure on the hydraulic brakes at individual wheels.” What the testers found Early reports were glowing. Popular Science writer Jim Dunne covered the system in November 1970. He reported a 40 percent cut in stopping distance on slippery surfaces, according to Hagerty. Dunne also wrote that the car made “firm, steady stops – even when driving on glare ice.” For anyone driving a big luxury sedan through a northern winter, that was a real selling point. Why buyers passed on it Price was the first problem. The 1971 Imperial started at just over $6,000, Hagerty notes, so the $351.50 option added nearly 6 percent. Jalopnik puts the cost at nearly $3,000 in today’s money. Chrysler trimmed the price to $344 for 1972 and 1973, but demand stayed low. Hagerty estimates that Sure-Brake went on fewer than 5 percent of Imperials through 1973. By its count, that meant a few hundred cars a year at most. In fact, Jalopnik argues the problem was partly understanding: “Buyers were hesitant to pay extra for an invisible computer module they didn’t fully understand.” As a result, Chrysler did not offer Sure-Brake for 1974, Hagerty says. Jalopnik also dates the end of the technology at Chrysler to 1974. Ford, Jensen and the race to stop skidding Chrysler wasn’t alone, but its system went further than the others. Ford’s Sure-Track, developed by Kelsey-Hayes, arrived in late 1969 on the Thunderbird and Continental Mark III for about $195, Hagerty reports. However, Sure-Track worked only on the rear wheels. It later became standard on the 1974 Continental Mark IV. The idea itself came from the sky. Aircraft used anti-skid brakes from the late 1940s, Hagerty says, and a purely mechanical aircraft system called Maxaret found its way into a car in 1966. That car was the Jensen FF, a four-wheel-drive version of the Interceptor grand tourer. Still, the FF never became a mass-market car. Only 320 were built through 1971, all with right-hand drive, and Jensen never officially exported the FF to the United States, according to Hagerty. The Imperial, by contrast, brought electronic four-wheel anti-lock brakes to an American showroom. Seven years before Mercedes For decades, Mercedes-Benz claimed its Bosch ABS was the first electronically controlled four-wheel anti-skid system in production. That system arrived in Europe in 1978, Hagerty notes. Even so, Hagerty credits the 1971 Imperial as first, while conceding that the Mercedes system “probably had an advantage with more modern digital controls.” In other words, Bosch got the digital brains right, but Chrysler and Bendix got there first. The Imperial’s analog setup proved the concept on public roads seven years earlier. Imperial Sure-Brake ended as a short experiment. Hagerty’s records show Chrysler sold the option for three model years, 1971 through 1973, at $351.50 and then $344. Chrysler did not offer it again for 1974.
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