A little while ago I wrote about drum brakes and it reminded me of the Le Mans winning Jaguars of the 1950s. One of the advantages the Jags had over their American, German and Italian rivals was their use of disc brakes. The other cars mostly still used drum brakes that were inferior in their ability to slow a car down. Thus the Jags could brake much later than the other cars going into a corner.
The first disc brakes appeared 50 years earlier – right at the start of the industry and they were invented by Edward Lanchester, whose company was bought by Jaguar in 1960 when they absorbed Daimler, who had themselves bought Lanchester back in 1931. Disc brakes were fitted to Lanchester cars for a while, however they weren’t that successful because the road infrastructure was lagging behind the technology and the materials used for the discs were being damaged by the rough road surfaces.
It was after the Second World War that several companies experimented with the disc brake. Crossley fitted them to a model in 1949 and Chrysler also fitted a form of disc brake to the Imperial around the same time. It was Dunlop who were developing braking systems during the 1950s that cracked the secret to reliable and efficient disc brakes and it was these that were fitted to the Le Mans winning Jaguar C-Type.
Citroen and Triumph introduced disc brakes on their road cars soon after the C-Type win and in 1954 the Austin–Healey 100 was the first production car to feature discs on each wheel. It took nearly 10 years before the American manufacturers caught up with Studebaker and Chevrolet fitting discs in the mid 1960s. These early versions were fitted close to the differential – a design still used in racing today. This is known as inboard brakes and helps to reduce the heat around the tyres. Most modern road cars have their discs mounted so that the wheel surrounds them and they are connected directly to the hub.
Dunlop’s discs were made out of cast iron however nowadays they are made from “grey” iron, a form of iron that has chemicals added to aid with the tensile strength and heat dissipation. On high end sports cars and racers, carbon ceramic discs are used for their increased strength and ability to retain their shape and performance under extreme heat conditions. Quite often high end sports cars and motorbikes also have drilled or slotted discs. These are designed to remove hot gases and water from between the disc and the pad which would impede their performance.
The other half of the braking system is the calliper that clamps the disc to provide the braking force. The caliper holds the pads – made of a variety of materials depending on usage – and it also holds the piston that applies the pressure. In industry jargon, a piston is called a pot, so if a calliper has 4 pistons then it is a 4-pot braking system. The pads used to be made of asbestos and now they are made with various materials, again including carbon and ceramics. Asbestos is now banned as a material to be used in any auto component due to health risks. I used race brake pads on my old Honda and these had a metal compound added. They were significantly more effective than standard pads, however they wore out much much quicker! They were also noisy until they reached the correct operating temperature.
Worn out pads can damage a disc and this will require the disc to be skimmed (at a minimum) to regain its shape. Discs can also warp if subjected to extreme and constant heat and they can be scarred if poor or worn pads are used. I saw an Aston convertible the other day ay a local mechanic with the worst discs I have ever seen. I should have taken a photo as they were beyond skimming with very deep grooves caused by worn pads and an inattentive owner.
The braking system is just one part of a group of technologies that need to be maintained to work well together. A car will brake well if the system has clean discs and plenty of material left on the pads – there are many after market manufacturers like Ferodo that can provide pads for differing conditions and uses. It is also important to ensure that the tyres still have plenty of rubber on them and that the suspension is not worn. Any problems with just one of these components will cause the brakes to have reduced performance.
Looking after your car will mean that when you need it to help you in an emergency it can do, thus reducing the risk of a major event.