July 22, 2024


Where Innovation Lives

The Rearview Mirror: The 1940s Technology That Underpins Your Car

4 min read


Earle MacPherson’s U.S. patent drawing for his strut suspension.

Most of the major components in an automobile date back decades, or even more than a century. The first internal combustion engine dates to 1860. The manual transmission is nearly as old. The first automatic transmission came to market in 1939. 

And given that until the 1970s, most cars didn’t have a MacPherson strut suspension, you’d expect it to be a relatively recent innovation, but you’d be wrong. If fact, its genesis dates to World War II, and was perfected shortly thereafter.

This week in 1947 Earle Steel MacPherson filed a patent for his new vehicle suspension system, now known as the MacPherson strut suspension.

A lifetime auto industry engineer

Earle MacPherson was working for Chalmers Motor Car Corp. when this 1917 Chalmers 6-30 was built. Photo Credit: RM Auctions.

MacPherson’s career in the automotive industry started after graduation from the University of Illinois in 1915, when he joined Detroit-based Chalmers Motor Car Co., one of America’s more popular cars at the time. After serving in the U.S. Army during World War I working on aircraft engines, he returned to Detroit. But MacPherson didn’t rejoin Chalmers.

Instead, he landed at the Liberty Motor Car Co., founded in 1916, whose vice president, James Bourquin, came from Chalmers. The Liberty is an assembled car using Continental engines rather than proprietary ones. Despite some success, the company begins to falter once they moved to a larger factory. MacPherson left in 1922, just as the company began sliding into receivership. 

He joined Huppmobile, where he remained until 1934 when struggles among Hupp shareholders led him to General Motors’ central engineering office, eventually becoming Chevrolet’s chief design engineer. 

A novel postwar sedan

The Chevrolet Cadet’s MacPherson strut suspension handled batter than a contemporary Cadillac, above.

During World War II, automakers were thinking about the postwar market. Their only guidance came from World War I, which saw a sudden deep recession hit, severely affecting car sales. Chevrolet managers were concerned an economy car might be needed. GM’s chairman, Alfred P. Sloan disagreed, saying the postwar economy would bring prosperity. But he let the project proceed.

Known as the Light Car, the four-door sedan was targeted to have a weight of 2,200 pounds. To reach that goal, MacPherson called for a 108-inch wheelbase, 8 inches less than contemporary Chevrolets. Since it didn’t weigh much, it wouldn’t need a big engine. So, a 2.1-liter inline 6 was specified, producing 61 horsepower, which was more than adequate for the time. 

Beyond minimizing unsprung weight, MacPherson wanted to make the car as roomy as possible. So MacPherson took a hard look at the car’s suspension. 

A radical approach to a traditional problem

Cars initially inherited their leaf spring suspensions from 19th Century horse carriages. While they had advanced from there, the MacPherson strut suspension proved novel.

A MacPherson strut supension patent drawing.

The strut itself is a combination of spring and shock absorber. The bottom part of the strut links to the wheel hub, while upper part of the strut mounts to the body, eliminating the need for an upper control arm. A lower control arm links the bottom of the wheel hub to the body.

By eliminating the upper control arm, and mating the shock that rides between the upper and lower control arms to an external spring, it frees up space for a front-wheel driveshaft. (This is why so many front-wheel and all-wheel drive cars use them more than seven decades later.) But the strut needed to mount to the body, requiring MacPherson to use unibody construction at a time when few, if any, cars used it. 

With fewer parts than traditional suspensions, the new suspension weighed and cost less yet proved stable and easy to adjust. It was also narrower and more compact than traditional suspensions, which freed up cabin space. For Chevrolet’s Light Car, now called the Cadet, it was used at all four corners. 

When the new car underwent tests at GM’s Milford Proving Grounds, its handling wasn’t only better than a Chevrolet, it was better than a Cadillac.

What killed the Cadet?

The MacPherson strut would finally be used not by GM, but by Ford of Europe in the Consul and Zephyr.

As is often the case, great engineering often runs afoul of accounting, and so it was with the Chevrolet Cadet.

General Motors wanted to sell the Cadet for $1,000 or less. But even at $1,000, the company would have to manufacture 300,000 units to be profitable. GM engineering vice president James M. Crawford insisted that the Cadet’s engineering be simplified and cheapened, and the project was postponed in 1946 before being killed the following year. Alfred Sloan had proven prescient; postwar prosperity and booming vehicle sales negated the need for an economy car.

MacPherson jumped ship and went to Ford Motor Co., and filed a patent application for the new suspension, filing a refined version two years later.

In the end, his suspension would debut on the 1949 Ford Vedette in France, followed by the Ford Consul and Zephyr in England. It wouldn’t appear on a General Motors car until the 1980 Chevrolet Citation, when General Motors relearned the lessons it first pioneered, then rejected, 34 years earlier. 

MacPherson would retire from Ford Motor Co. as engineering vice president, dying in Detroit in 1960 at the age of 69 years old.


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