Disc brake
After the war, technological progress began in 1949, with caliper-type four-wheel disc brakes on the Crosley line and a Chrysler non-caliper type.
In the 1950s, there was a demonstration of superiority at the 1953 24 Hours of Le Mans race, which required braking from high speeds several times per lap.
The poor state of the roads at this time, no more than dusty, rough tracks, meant that the copper wore quickly, making the system impractical.
Patented by the British Motorcycle & Cycle-Car Research Association, Douglas described the device as a "novel wedge brake" working on a "beveled hub flange".
[16] Crosley four-wheel disc brakes made the cars, and Crosley-based specials, popular in SCCA H-Production and H-modified racing in the 1950s.
[16] This four-wheel disc brake system was built by Auto Specialties Manufacturing Company (Ausco) of St. Joseph, Michigan, under patents of inventor H.L.
[16] In 1953, 50 aluminum-bodied Austin-Healey 100S (Sebring) models, built primarily for racing, were the first European cars sold to the public to have disc brakes, fitted to all four wheels.
"[5] Before this, in 1950, a Crosley HotShot with stock four-wheel disc brakes won the Index of Performance in the first race at Sebring (six hours rather than 12) on New Year's Eve in 1950.
[4] Despite early experiments in 1902, from British Lanchester Motor Company, and in 1949 from Americans Chrysler and Crosley, the costly, trouble-prone technology was not ready for mass production.
[30] The Bendix units were optional on all American Motors' Rambler Classic and Ambassador models as well as on the Ford Thunderbird, and the Lincoln Continental.
Lambretta introduced the first high-volume production use of a single, floating, front disc brake, enclosed in a ventilated cast alloy hub and actuated by cable, on the 1962 TV175.
Although this gave the brake pads better cooling, it is now almost universal practice to site the caliper behind the slider (to reduce the angular momentum of the fork assembly).
Improved technology has seen the creation of vented discs for use on mountain bikes, similar to those on cars, introduced to help avoid heat fade on fast alpine descents.
In the U.S., drums are allowed and are typically preferred for their lower purchase price, despite higher total lifetime cost and more frequent service intervals.
Should the braking energy exceed the maximum, for example during an emergency occurring during take-off, aircraft wheels can be fitted with a fusible plug[47] to prevent the tire bursting.
For normal car and light-truck applications, SAE specification J431 G3000 (superseded to G10) dictates the correct range of hardness, chemical composition, tensile strength, and other properties necessary for the intended use.
Reinforced carbon discs and pads inspired by aircraft braking systems such as those used on Concorde were introduced in Formula One by Brabham in conjunction with Dunlop in 1976.
[49] Carbon–carbon braking is now used in most top-level motorsport worldwide, reducing unsprung weight, giving better frictional performance and improved structural properties at high temperatures, compared to cast iron.
Due to the high heat tolerance and mechanical strength of ceramic composite discs, they are often used on exotic vehicles where the cost is not prohibitive.
Porsche's Composite Ceramic Brakes (PCCB) are siliconized carbon fiber, with high-temperature capability, a 50% weight reduction over iron discs (hence reducing the vehicle's unsprung weight), a significant reduction in dust generation, substantially extended maintenance intervals, and enhanced durability in corrosive environments.
The machining process is performed in a brake lathe, which removes a very thin layer off the disc surface to clean off minor damage and restore uniform thickness.
When the hotter sections of the discs reach extremely high temperatures (1,200–1,300 °F or 649–704 °C ), the metal can undergo a phase transformation and the carbon which is dissolved in the steel can precipitate out to form carbon-heavy carbide regions known as cementite.
[citation needed] Scarring (US: Scoring) can occur if brake pads are not changed promptly when they reach the end of their service life and are considered worn out.
Manufacturers that use drilled discs as OEM typically do so for two reasons: appearance, if they determine that the average owner of the vehicle model will prefer the look while not overly stressing the hardware; or as a function of reducing the unsprung weight of the brake assembly, with the engineering assumption that enough brake disc mass remains to absorb racing temperatures and stresses.
Over time, vented brake discs may develop severe rust corrosion inside the ventilation slots, compromising the strength of the structure and needing replacement.
Floating caliper (single piston) designs are subject to sticking failure, caused by dirt or corrosion entering at least one mounting mechanism and stopping its normal movement.
Sticking can result from infrequent vehicle use, failure of a seal or rubber protection boot allowing debris entry, dry-out of the grease in the mounting mechanism, and subsequent moisture incursion leading to corrosion, or some combination of these factors.
This allows the metal-to-metal parts to move independently of each other and thereby eliminate the buildup of energy that can create a frequency that is heard as brake squeal, groan, or growl.
Hot spots are classified as concentrated thermal regions that alternate between both sides of a disc that distort it in such a way that produces a sinusoidal waviness around its edges.
DTV is usually attributed to the following causes: waviness and roughness of disc surface,[72] misalignment of axis run-out, elastic deflection, wear and friction material transfers.
