Anti-lock braking systems were first developed for aircraft by Dunlop back in the 1950s and were a fully mechanical system. They were introduced in the 1960s in the Ferguson P99 racing car, the Jensen FF and the experimental all wheel drive Ford Zodiac, and later in the Ford Fiesta Mk III, but were expensive and somewhat unreliable in cars. The German firm Bosch had been developing anti-lock braking technology since the 1930s, and their electronic system was first used in production cars in 1978. They first appeared in trucks and German limousines from Mercedes-Benz. Systems were later introduced for motorcycles.
The anti-lock brake controller is also known as the CAB (Controller Anti-lock Brake), which has a central electronic unit connected to four speed sensors (one for each wheel) and several hydraulic valves on the brake circuit. By monitoring the rotation speed of each wheel about 10 times a second, it can sense the instant that a wheel is rotating slower than the others (which can cause the wheel to lock) and adjusts the valves to decrease the pressure on the brakes on that wheel. The brake pressure on each of the four wheels can be computer-adjusted several times a second through the braking process.
The heavier a vehicle is, the more it will benefit from ABS, especially those with less-sophisticated hydraulic braking systems lacking the fine control of more developed braking systems. Conversely, lighter vehicles and sports cars with highly-developed braking systems without ABS can out-brake comparable vehicles with ABS.
When activated, the ABS causes the brake pedal to pulse noticeably, which can be a little disconcerting in your first emergency braking action. A driver should continue with full braking pressure until the vehicle is stopped, and let the ABS do the "thinking". Some manufacturers have therefore implemented "brake assist" systems that determine the driver is attempting a crash stop and maintain braking force in this situation.
With ABS, regular checkups should not only look at the 'friction material' as brake pads and shoes, but include a look at the hydraulic side of the car's braking system needs preventive maintenance. All cars should have their brake fluid regularly flushed out and replaced with fresh fluid. The ABS modulator unit may get damaged if the fluid in it is either dirty or moisture-contaminated, so owners are recommended to flush and replace the fluid every 2 years or 36,000 kilometres.
If you are planning to work on the brakes of an ABS-equipped vehicle read the service procedures before starting, consulting the appropriate shop manual for the vehicle, and taking all recommended precautions.
For example, the modulator may contain brake fluid under pressure and must be depressurized before any work can be done (some brands of modulator operate under little or no pressure, so check your manual).