Anti-lock braking systems (ABS) prevent a car’s wheels from locking up during hard braking, so the tires keep grip and the driver can still steer. Sensors monitor each wheel’s speed; if one is about to lock, the system rapidly releases and reapplies brake pressure many times per second. ABS began in aircraft, appeared in early mechanical form on cars in the 1960s, and the modern electronic four-wheel ABS was introduced by Bosch and Mercedes-Benz on the 1978 S-Class. It became the foundation for traction control and electronic stability control.

Timeline

Year Development
1950s Anti-skid systems in aircraft
1966 Mechanical anti-lock on the Jensen FF
1971 Early electronic systems on some U.S. luxury cars
1978 Bosch electronic four-wheel ABS on the Mercedes S-Class
1990s–2000s ABS becomes standard on most cars

How ABS works

  1. Wheel speed sensors measure how fast each wheel is turning.
  2. The control unit detects when a wheel is slowing much faster than the car — about to lock.
  3. Valves in the hydraulic unit reduce, hold and reapply pressure to that wheel, many times per second.

Drivers feel a pulsing in the brake pedal, which is normal — keep pressing firmly.

Why it matters

A locked wheel slides and cannot steer. With ABS, the driver can brake hard and steer around an obstacle. On wet or slippery roads it helps maintain control.

The S-Class debut

Mercedes and Bosch spent years developing a reliable electronic system. Its introduction on the W116 S-Class in 1978 marked the start of modern ABS. Read the W116 S-Class and S-Class safety firsts.

The foundation for more

ABS sensors and hydraulics made possible traction control, electronic stability control and automatic emergency braking. Read electronic stability control history and automatic emergency braking.