The History of Automotive Brake Systems
"Ninety-nine percent of you is invisible [...]"
- Buckminster Fuller
Even as brake system experts we don't think about our brakes too often. Brakes are brakes, and despite how ingenious their design is, often they stay "ninety-nine percent invisible." In his quote about being 99% invisible his reference is philosophical, but it's a concept which applies to the world abroad-- including your brake lines. In this overview, we'll dive into that 99% by covering the evolution of brakes, the challenges thrown against brake systems, servicing considerations, and brake system design requirements.
Consider Newton’s First Law of Motion: an object that is put into motion will stay in motion unless it is acted upon by some external force. This is the principle behind brakes; vehicles gain energy from burning fuel to put it in motion, then they must act upon theirselves to bleed off that gained energy. Certainly some environmental factors can do this: air resistance, gravity, drivetrain loss, and even just friction with the ground, but the most efficient way to bleed energy is with brakes.
Modern brake pads and shoes generate the friction necessary to stop a car, but even earlier wheeled vehicles like oxcarts and carriages required brakes. Up through the time of steam-driven automobiles of the 1880’s, stopping power was achieved with blocks of wood which could be pressed against the side of steel-rimmed wheels with a lever and rod. Then around 1880 came Michelin with the production of solid rubber tires which revolutionized small-scale wheeled travel. Suddenly wood blocks weren't a tenable braking method any more.
It was at around this point near the turn of the century that things in the braking world started to change exponentially. Horse-drawn travel was gradually giving way to steam and gasoline engine, road speeds were increasing, and the automotive world needed a better solution to bleeding off momentum. Two of the most famous names in the motoring world rose to the challenge: Gottlieb Daimler and Louis Renault. Daimler envisioned that a cable could be wrapped around a big drum that could then be bolted to the vehicle chassis. While it was Daimler who had the original idea, Renault ran with it, creating the first functional design. Soon, the first production-ready drum-and-cable brake system was developed for a Mercedes. They were mechanical, and operated with a hand-lever
This early drum brake execution was revolutionary, but it had some major downsides; the external cable arrangement would frequently slip on hills, and the metal-on-metal design didn’t last long at all and required constant adjustment. Safety and longevity were major problems with this new brake system. Gradually, however, metal cables and bands gave way to woven asbestos and copper brake linings, improving stopping power. Yet even these braking systems remained completely external and operated on only one axle until around 1915 when mechanically-connected 4-wheel brakes started to enter the scene. Early on, these 4-wheel braking systems were considered to be top-tier options, if not an outright luxury: the 1915 Duesenberg racer was equipped with the new style of braking system.
Soon after Renault's design took off it was determined that moving the friction pads inside of the drum produced improvements in both braking consistency and brake pad life, and they took the industry by storm. Internal-expanding drum brakes remained mechanically actuated through 1918 when Malcolm Lockheed began development of the first hydraulic braking systems. The decision to integrate hydraulic technology with braking systems was another leap in the technology of brakes. This earliest hydraulic system concept used a single pedal to transfer force from the main cylinder through a series of tubes and cylinders to the brake shoes, thus reducing the amount of force needed by the operator to slow the vehicle and increasing system reliability.
The Lockheed design saw its first practical application in 1921, but these early hydraulic systems were notorious for leakage issues. The automotive scene was a mix of mechanical and hydraulic systems through the early 1930’s. Some of the high-end domestic manufacturers and many of the European’s committed to the hydraulic design, where GM and Ford remained traditionalists, using mechanical brakes through the mid-1930’s. Interestingly, while Ford is lauded for their forward-thinking mass production techniques in the automotive world, they remained one of the last holdouts when it came to switching brake systems: they only moved to hydraulic brakes in 1938 after finally abandoning a design where a mechanical drum brake was fitted inside the transmission case.
4-wheel hydraulically-operated internal-expanding shoe-drum brakes remained the standard for domestic production right up into the 1970’s… Then things got interesting: enter disc brakes! The original concept of caliper-contained brake pads was developed by British engineer William Lanchester all the way back in 1902, but they arrived later on in US designs. European manufacturers were focused more on vehicle speed capabilities and understood that disc brakes offered promising advantages in terms of heat dissipation: disc brakes shortened stopping distance and reduced vehicle weight. Early adopters of disc brake systems included Mercedes-Benz, Renault and Lancia all around 1960 and by the mid-60’s Nissan and Volvo. The 1949 Crosley Hotshot was the United States' first domestic-production vehicle to be equipped with disc brakes, but the system didn’t catch on until the 1970’s.
Today, front-disc, rear-drum and double-disc configurations are the norm. The noise problems that plagued early disc brake systems have largely been overcome and- frankly- manufacturers have relied on hydraulic designs for a while now, but let’s not forget two other significant milestones in brake system design: self-adjust and power assist features. While there were some early attempts at self-adjusting brakes in the mid-1920’s, the concept really didn’t take hold until Wagner Electric marketed the idea in the mid-1940’s. So why is self-adjustment such a remarkable innovation? As brake shoe friction material wears, the distance between the shoe and the drum increases to the point that an adjustment must be made to bring the two surfaces into closer proximity and reduce brake pedal travel. Prior to self-adjusters, involved brake service was frequently required. Now self-adjusters are common, and a screw or wedge automatically adjusts the brake shoes to keep them in good content.
Power-assisted brakes (“power brakes,” for short) generally use a vacuum canister which utilizes intake manifold vacuum to assist in the application of hydraulic pressure, thus reducing the amount of pedal pressure required to slow the vehicle. Vacuum-assisted brakes were in general production for high-end vehicles by the early 1930s and have found their way to practically every production passenger car and light truck today. Vacuum assist is usually associated with gasoline-powered vehicles like Diesels, which operate without enough intake manifold vacuum to operate a brake booster. For Diesel vehicles, various hydraulic assist mechanisms have been applied to reduce brake pedal effort.
We established early on in this article that better braking systems were needed due to increases in vehicle speed. As vehicle speeds have increased, safety has become the paramount consideration for automotive designers. A result of this new need was the development of the anti-lock brake system (ABS). ABS was originally invented in the 1930s to reduce the chance of an aircraft skidding off the runway. By the 1950s, ABS had found its way onto a limited number of automotive applications, spearheaded primarily by Mercedes-Benz and Bosch Corporation.
Advances in modern electronics have led to rapid advances in the sophistication of automotive ABS systems. Broken down, the ABS system consists of wheel speed sensors, a processing computer, and a hydraulic modulator. The wheel speed sensors generate frequency signals that are read and constantly interpreted by a dedicated ABS computer. This computer contains complex algorithms called maps that continually compare the sensor inputs between any given wheel and the other three, and then this data is compared against the map. During hard or panic braking, one or more wheels may lose traction; the ABS system then acts to regulate hydraulic pressure to the affected wheel(s) to optimize stopping distance. It does this through three sets of lightning-fast calculations for the rapid pressure build, pressure hold, and pressure release cycles. Often, the driver will notice what feels to be a grinding or vibrating sensation during hard braking: this is the ABS doing its job and regulating the pressure of the brakes. ABS has done a remarkable job in reducing stopping distance, and can be combined with other functions such as automatic stability regulation (ASR) to increase safety and performance even more.
The extensive use of all this complex, computational technology raises a question: have these super-advanced systems put servicing and repair of modern brake systems out of the reach of independent repair shops and DIY mechanics? Not at all! There is an abundant amount of information from the internet, repair books, and journals to perform most automotive repair work independently: everything from a simple brake pad replacement to a more involved task such as replacing brake lines. Fortunately, innovation and thoughtful repair solutions are equally abundant in the solutions presented by the automotive aftermarket.
We often see “pattern failure” occur in-vehicle systems and components years after the vehicle was produced. Braking systems are far from immune to these sorts of problems. For example, let's examine General Motors full-size pickup trucks and sport utility vehicles, produced from the mid-1990s through the mid-2000s. Hydraulic brake tubing ("brake lines," for short) are known for rusting and failing at an above-average rate, and if a brake line fails hydraulic pressure fails to be delivered to that wheel and the brakes won't engage. As with most vehicles, the original equipment (OE) brakes lines are made of mild steel, which is notably rust prone. Lines like these are Zinc-galvanized to add a layer of protection around the tubing, but offer little long-term protection from the elements. Our team at 4LTL sees this problem often, and we like to think that they are becoming a part of automotive innovative history by offering an innovation of their own: Copper-Nickel brake line. Copper-Nickel is the perfect choice for brake lines because the alloy used affords all of the material-quality benefits of steel lines with none of the drawbacks. Steel rusts and corrodes if not carefully maintained, especially in rust-belt states. Copper-nickel tubing does not. Copper-nickel tubing bends easily by hand but stays rigid and strong, standing up to both the internal pressure of your vehicle's hydraulic fluid and the external conditions of a car's undercarriage. It flares quickly and uniformly, and with 4LTL you can even purchase pre-flared and pre-fitted kits with rust-resistant black-oxide finished tube nuts.
Ninety-nine percent of a car is invisible. The mechanisms, the manufacturing process, and the history are lost when you're actually driving the vehicle0 . Learning about that 99% and keeping it in good order takes a lot of work, but the 4LTL team hopes that this article has been illuminating. We love being a part of this industry because it's always progressing into the next best solution, and we hope we can be part of yours.
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Best of luck on your next project,
the 4LTL team.