Developed for airplanes in the 1930s, anti-lock brake systems (ABS) were first installed on passenger vehicles in the 1980s. By the end of the millennium (or the beginning of the current one depending on whether you see the glass as half-full or half-empty) about one-third of the cars in America were equipped with ABS. That is long enough for some to have not known a time when ABS was not available.
According to the ABS Education Alliance, a coalition of ABS companies, the original system was patented as the antiblockierysystem in Germany in 1936. While early on it had its detractors, ABS has been called one of the most significant safety advances in automotive engineering by many in the transportation industry and government.
As you most likely know, ABS prevents your wheels from locking up and your car from skidding in a panic stop.
Many of us learned in driver’s ed that it was best to pump the brakes on a slippery or snow-covered road to improve the ability to stop and avoid sliding off the road or hitting something. This works, but not perfectly. After all, how fast can a human pump the brake pedal? Certainly not as fast as ABS, which does so up to 18 times per second.
Though anti-lock brakes have been around for more than two decades, many motorists do not know how to best use their ABS-equipped car or truck. Even fewer know how the system works.
There are two basic types of ABS. The first, on cars and some light trucks, is four-wheel anti-lock. The other operates only on the rear wheels and is on some pickup trucks. Without much weight in the bed, pickups tend to slide sideways or spin under hard braking, even on dry pavement.
And just because your car has ABS, you can’t drive like a demon and expect the brakes to save you. Basically, by preventing wheel lockup, ABS can help you avoid a collision by allowing you to maintain steering control while stopping–without skidding–in the shortest possible space. That space may be insufficient if you don’t allow adequate following distance.
When you mash on the brake pedal, the system modulates the brake pressure to each of the four wheels independently. If only one or two wheels are about to lock up, the brakes for only those will be modulated.
When the ABS is activated, you may hear a chattering noise and may feel the brake pedal pulsating. This is normal so don’t take your foot off the brakes–keep them firmly applied. On some newer cars, the noise and vibration are almost eliminated, though.
If you have never felt your ABS system in operation, find a safe place to practice in slippery conditions, like when the first snowfall arrives.
The mechanics of the ABS system are simple. Speed sensors at each wheel send signals to a processor. As long as all of the wheels are rolling at nearly the same speed, the processor does nothing. It just waits until it gets an input from the brake light switch alerting it that the brakes are being applied. Then, if one or more of the wheels slows down significantly, the processor sees this as imminent lock-up and jumps into action. It sends signals to the ABS modulator valve assembly (usually under the hood near the master cylinder) that applies the brakes to that wheel.
If, however, that wheel’s rotation almost stops, the pressure is released then reapplied rapidly and repeatedly. This is what keeps the wheels from locking up and what causes the pedal feedback.
If your car has ABS, a light on the dash will glow if something should go amiss with the system. When that happens, your brakes will work fine, just as though your car was not equipped with ABS. The light will come on briefly when you start the car to let you know the bulb is working. But if it stays on as you drive, get your ABS fixed.
We hope you won’t be flying down the Kennedy, Edens or Stevenson in the snow this winter. But even at safe speeds, ABS may help you avoid crashing.
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Bob Weber is an ASE-certified Master Automobile Technician, having recertified every five years since 1978. Contact him at MMTribune@netscape.net.
Dos and Don’ts
Four-wheel ABS is a safe, effective braking system when used properly. It offers an important safety advantage by preventing the wheels from locking during emergency braking situations, allowing drivers to maintain control over steering and operate vehicles more effectively. To take full advantage of the maximum safety benefits, drivers must learn how to operate their anti-lock braking systems correctly.
DO
– Keep Your Foot on the Brake. Maintain firm and continuous pressure on the brake while steering to enable four-wheel ABS to work properly. Avoid pumping the brake, even if the brake pedal is pulsating. In vehicles that are equipped with rear-wheel anti-lock brakes, however, the front wheels can still lock up the same as conventional brakes. If that happens, the driver should ease up on the brake pedal with just enough pressure to allow the front wheels to roll again so he/she can steer.
– Allow Enough Distance to Stop. Follow three seconds or more behind vehicles when driving in good conditions. Allow more time if conditions are hazardous.
– Practice Driving with ABS. Become accustomed to pulsations that occur in the brake pedal when ABS is activated. Empty parking lots or other open areas are excellent places to practice emergency stops.
– Consult the Vehicle’s Owner’s Manual for additional driving instructions on the anti-lock brake system.
– Know the Difference Between Four-Wheel and Rear-Wheel ABS. Four-wheel ABS is generally found on passenger cars, and is designed to maintain steerability in emergency braking situations. Rear-wheel anti-lock brakes, found exclusively on light trucks, vans and sport-utility vehicles, is designed to maintain directional stability and prevent the vehicle from skidding sideways.
DON’T
– Drive an ABS-Equipped Vehicle More Aggressively than vehicles without ABS. Driving around curves faster, changing lanes abruptly or performing other aggressive steering maneuvers is neither appropriate nor safe with any vehicle.
– Pump the Brakes. In four-wheel ABS-equipped vehicles, pumping the brake turns the system on and off. ABS pumps the brakes for you automatically at a much faster rate, and allows better steering control.
– Forget to Steer. Four-wheel ABS enables drivers to steer in emergency braking situations, but the system itself does not steer.
– Be Alarmed by Mechanical Noises and/or Slight Pedal Pulsations while applying the brake in an ABS-equipped vehicle. These conditions are normal and let the driver know ABS is working.
Sources: ABS Education Alliance, a coalition of three companies that represent anti-lock brake manufacturers in the United States: Robert Bosch Corporation, Delphi Automotive Systems and Continental Teves.
— Bob Weber
