The Eagle was the kind of segment-busting product that engineers and marketers spend entire careers trying to create.

The company, an amalgamation of respected old US brands like Nash, Hudson and Willys, was perpetually a decade late and a few million dollars short of Detroit’s Big Three – Chrysler, Ford and General Motors. Though the company, known universally as AMC, hung on by its fingernails through the 1970s, it is best known for homely, temperamental vehicles – indeed, lemons – such as the Gremlin, Pacer and Concord.

In 1979, all of the company’s cars were saddled with desperately obsolete hardware that would have looked at home in cars 25 years older. Yet in this mixed bag was a honey pot named Jeep, which had the transformative power to turn a lemon like the Concord into pure lemonade. Adapting Jeep technology to road use, the car became the 1980 AMC Eagle, the first full-time all-wheel-drive passenger car to reach mass production.

Just as Jeep can stake a claim to the invention of recreational off-roading, it also claims parentage of the world’s first crossover vehicle, an all-wheel-drive station wagon with an extra three inches of ground clearance. Subaru, mind, manufactured cars that made do only with part-time four-wheel-drive, installed in cars with no additional clearance.

The Eagle was, in essence, the kind of segment-busting product that engineers and marketers spend entire careers trying to create.

Earlier Jeeps used full-time all-wheel-drive, but they lacked the sophistication of the Eagle’s system, which was supple enough for use in a car rather than an off-roader. Also, unlike Jeeps of the era, the Eagle employed a car-like independent front suspension.

At the heart of the Eagle was a viscous hydraulic single-speed transfer case, a technology that has been at the heart of some of today’s most popular all-wheel-drive cars and crossovers. The device, created with the assistance of FF Developments, known for its contribution to the exotic Jensen FF, allowed the Eagle’s front and rear wheels to rotate at different speeds when needed, but also kept them from spinning wildly in low-traction conditions. In effect, the transfer case provided a primitive mechanical form of traction control. Because it equalised wheel speed, whether the car was accelerating or braking, it also provided a measure of anti-lock braking effect.

The Eagle was available as a two-door sedan , two-door liftback, four-door sedan or four-door wagon, but it was the latter that found broadest adoption, leading AMC to drop the two-door.

The recipe worked so well that AMC sprinkled some AWD sugar on its slow-selling compact models, creating the Eagle SX/4. This was an all-wheel-drive coupe based on the AMC Spirit, providing a template for rally-inspired AWD sport compacts like the Subaru WRX and Mitsubishi Evolution. AMC even bolstered the Eagle range during 1981 and ’82 with the odd-duck Sundancer convertible

The original mid-size Eagle was powered by AMC’s ancient 4.2-litre inline six-cylinder engine. Its 1970s emissions technology choked the engine to an output so hopelessly low that the official spec sheet from 1979 excluded that information entirely. The smaller SX/4, betraying its massive rear spoiler and alloy wheels, offered a gutless version of General Motors’ archaic “Iron Duke” 2.5-litre inline four-cylinder engine. But if the power plants were antiquated and the chassis behind the times, the all-wheel-drive system was cutting edge, and it provided some valuable benefits.

For drivers, the Eagle created the all-weather security and peace of mind that has since propelled vehicles so equipped to dizzying sales, even outside snowy climes. And for AMC, the Eagle brought financial security that kept the company afloat for eight more years, until it was acquired by Chrysler in 1987.

The new owner had no interest in selling obsolete cars, but it did want Jeep and the all-wheel-drive technology of Eagle. AMC’s name disappeared with the acquisition, but the Eagle name carried on, worn by various Renault- and Mitsubishi-sourced models through the ‘90s, when it was finally retired in 1998.

Alas, being a trail-blazer is no guarantee of longevity.