Two car lengths? Do you expect the car to stop as though you had hit a solid wall? At what speeds are you going that the car can stop that quickly? ABS systems are supposed to stop working below about three to five miles per hour.
First you need to understand the purpose of anti-lock brakes. It has nothing to do with stopping distances. I've test-driven Caprice Classic county police cars after aligning them and had the chance to experience them with and without anti-lock brakes. A skidding tire has no traction and will slide easier than one that is braking near but not beyond its maximum traction. A real lot of trucks have rear-wheel-anti-lock brakes to prevent the rear of the truck from passing the front when the rear wheels lock up. Cars have a higher percentage of total weight on the rear tires so it makes sense to have anti-lock brakes on all four wheels.
The purpose of all anti-lock brakes is to let you maintain steering control, period. If your front tires are skidding during a panic stop, you can turn the steering wheel all you want to, but you're going to slide straight ahead into that other car. Non-skidding tires allow you to steer around the obstacle.
Getting back to my sad police car story, applying the brakes as hard as possible without locking up any brake will stop those cars much faster than those with anti-lock brakes. With those with ABS, the car will go and go and go, and they'll find you in the next county before the car stops, but you'll always have steering control.
Those cars used the Bendix-9 ABS system. I have a '93 Dodge Dynasty with the Bendix-10 system. The only difference is on the Caprice, when either rear wheel is about to lock up, brake pressure is reduced to both rear wheels together. On my Dynasty, each rear brake is modulated independently. There's more to the story than that because in my Dynasty you'll just about tear the seat belts off their hinges, even when panic-stopping on sand. To understand why, you have to go back to the "skidding tire has no traction". If you have to panic-stop and you hear one tire starting to skid, you'll stop faster if you let up on the brake pedal a little to keep that tire rolling. So you let up on the brakes, but the other three tires weren't at their maximum stopping power yet. Anti-lock brake systems look at all four wheels and keep all four of them spinning even though they are all near their maximum stopping power. All the while this is happening, you have steering control.
Chrysler was the first to have an anti-lock brake system in 1969. Unfortunately it only pulsed the brakes three times per second, which you can do with your foot. Newer systems can pulse the wheels up to 30 times per second, but 15 times is more typical. The valves turning on and off are the buzzing noise you hear when the system activates.
The reason they used to teach you to pump the brake pedal was many driver's can't adjust brake pedal pressure accurately to achieve maximum stopping power while maintaining steering control. Pumping the pedal makes some tires skid, then release, skid, then release. It takes time for a skidding wheel to start rolling again, and by the time it does, you're pressing the pedal again. All ABS systems are much more effective because they never allow a wheel to completely stop turning. Also, they never reduce braking power to any wheel that is not near losing traction. The systems keep each wheel close to its maximum stopping power, but that's just the side benefit. The systems' purpose is to maintain steering control.
Tuesday, January 5th, 2016 AT 8:50 PM