Automotive Anniversary: 70 years of the disc brake

Numerous automotive technologies are the result of innovations fostered within the aerospace and defence industries – which, unfortunately, does mean that much has its roots in developments focused on improving military hardware.

Direct petrol injection, for example, was developed by Bosch in the late 1930s to increase the performance and reliability of German fighter aircraft engines. Some twenty years later, the same expertise was employed to produce the first direct-injected petrol passenger car – the Goliath GP700 Sport of 1951; the direct-injected Mercedes-Benz 300 SL (pictured below) would follow in 1954, yet garner more attention due to its high-performance nature.

DEVELOPED FOR MILITARY USE

It is a similar story with concepts such as turbocharging, supercharging, head-up displays, engine management systems, sequential and compound forced induction, hemispherical combustion chambers and nitrous oxide injection. These, although sometimes not originating from military-related research, were refined and employed in earnest in the pursuit of improved air power.

Not all were designed to grant an edge in combat, that said, as some technologies were instead focused on protecting the crew – or making the task at hand less complicated.

Reliable anti-lock brakes, for one, were the result of efforts to ease the process of stopping aeroplanes. The terrific pace of aerospace development during World War II had resulted in aeroplanes that were faster, heavier and more complicated; they were subsequently more challenging to stop and improper application of the brakes could lead to excessive tyre wear, longer stopping distances or worse.

As a result, production anti-lock braking systems such as the Hydro-Aire Hytrol Mk1 were developed in the late 1940s – with it first being employed in the Boeing B-47 Stratojet to help reduce the workload of the crew and assist in safely and steadily stopping the six-engined bomber.

ANOTHER STOPPING POWER DERIVED FROM THE AEROSPACE INDUSTRY

Safety systems such as the aforementioned ABS were not the only braking-related improvement sourced from aviation. In the early decades of flight, drum brakes were used to provide stopping power when on the ground. As the performance and weight of aircraft increased, and the braking demands rose, the drum brakes themselves also had to get bigger and heavier.

Aside from the obvious implications, bigger drum brakes were difficult to package and manufacturers began encountering clearance and design issues with the landing gear and wheels. Fortunately, in 1902, British engineer Frederick Lanchester had patented a type of brake that was compact, powerful and reliable – the disc brake. It adopted some concepts that had been explored in the late 1800s, and did away with the need for a bulky drum, brake shoes and often fiddly operating mechanism.

Instead, Lanchester’s design featured a rotating disc to which friction pads were clamped by a caliper. This set-up, among its other benefits, could dissipate heat better than a drum and also deliver more consistent braking.

THE DISC BRAKE AND AUTOMOTIVE APPLICATIONS

Material problems made Lanchester’s disc brakes unworkable at the time but, during the 1920s and following other developments, they finally became a viable option. Companies such as Sikorsky introduced multi-disc systems for its aircraft during the 1920s, for example, which delivered improved stopping power in a more capable, compact and straightforward package – one which was also often lighter. Unsurprisingly, as the aerospace industry quickly improved and demonstrated their effectiveness, the use of disc brakes spread.

In the automotive world, Jaguar is often cited as being the first manufacturer to adopt disc brakes in earnest. It adopted a set-up produced by Dunlop for its C-Type race car (pictured above) in 1952 which, after some development to combat heat-related issues, delivered excellent and reliable stopping power that gave the C-Types the advantage they needed to eke ahead of their rivals.

A NICHE OBSCURE MANUFACTURER TAKES THE DISC-BRAKED CROWN

Other manufacturers would soon begin offering disc brakes, including Citroen in 1955; the ever-graceful DS, which was packed with innovative features, had front disc brakes. Jensen and Austin-Healey also launched cars, in the same year, which were available with disc brakes all round.

However, all were beaten to the disc-braked punch in 1949 by America’s first post-war sports car – the Crosley Hotshot. This compact, affordable and economical roadster was offered with ‘ultra modern airplane type hydraulic brakes’ – a disc brake set-up called ‘Hydradisc’, which was an adaptation of the Goodyear-Hawley aircraft braking system.

It was not to prove successful, alas, due to problems resulting from winter road salt that corroded the calipers. Crosley subsequently reverted to drums later in 1950 but, in any case, 70 years ago you could indeed go out and buy a car with all-round disc brakes.

THE DISC BRAKE BECOMES COMMONPLACE

Chrysler also experimented with a production braking system that utilised discs at each corner, in 1949, but they were of a very different and short-lived configuration that bore little resemblance to the Crosley or any modern automotive set-up.

Regardless, the benefits were clear for all to see – and front disc brakes were soon commonplace. Drum brakes remained the norm for the back axle for decades to come, often for cost and simplicity reasons, but today they are far less common on new cars.

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