Auto, Truck ABS or Antilock brake systems,problems,help,diagnosis

If you drive a vehicle less than 10 years old, it's probably equipped with some type of Anti-lock Brake System, or ABS.
Most drivers never "use" this feature of the car, but it can prevent accidents, especially in a panic stop with a less experienced driver.

THE PURPOSE OF ABS

First some basics:

WHAT MAKES A CAR STOP?

I'm not going into how hydraulic brakes work: see my article on brakes to learn more about that.
You press the pedal, the wheel and tire start to slow down, slowing the vehicle down also. At some point, if you press the brake pedal hard enough, the wheel will "lock up." At this point the wheel is no longer turning, but the vehicle is still moving. The tire is skidding, and a skidding tire has very little traction. It is no longer slowing the car down nearly as fast as when the tire had traction and the brake pads were slowing it down.

It's kind of like "burning rubber" on a hot rod, but in reverse... You can spin the tires on a hot rod and make a lot of smoke and noise but not move an inch.

When your tires squeal on braking you aren't slowing down much.

The old driver's trick for this is to release the brakes and then re-apply them. The old adage used to be that you should "pump your brakes" in a panic stop. I never advocated "pumping" exactly: a good driver senses a skid and releases the brakes slightly, maintaining a pressure just short of the tire skidding.

Still, every driver on the road is NOT an expert driver. Often a driver will "freeze" in a panic stop, press the brakes as hard as they can, and skid into the object they were stopping for.

ANTILOCK BRAKES TO THE RESCUE!!!

Car makers developed antilock brakes many years ago, but recently with the advent of cheap computer stuff (along with the "encouragement" of U.S. auto Safety Regulators) they've started putting ABS on just about every vehicle.
The ABS computer senses the speed of the wheels through sensors at each wheel. When a wheel slows down a lot slower than all the other wheels, the computer releases the brakes on that wheel. Almost immediately the computer re-applies the brakes. The computer is, in effect, "pumping the brakes" for you, but doing it much faster than you could.

SAFETY WARNING:

When the ABS operates the rapid applying and releasing, or "pumping" of the brakes by the computer makes a rather loud noise and vibration. The first time I worked on a car with ABS I thought I'd check it out. When the ABS "kicked in" during my "test" I thought I had broken something on the car! The vibration freaked me out!

When ABS was first introduced a trend was noticed: rear end collisions actually INCREASED in cars with 4 wheel antilock brakes. The theory was that the noise and vibration they make "freaked out" drivers, who released the brake, then rear ended the car in front of them.

MY ADVICE:

Get out on an open stretch of road with no one around and try stopping as hard as you can a few times. Get used to the "ABS experience" so the vibration ABS makes won't freak you out if the ABS system activates in a panic stop.

If the ABS "kicks in" during a panic stop, don't release the brakes. It should stop you as fast or faster than an "expert driver" in the same circumstance, "pumping his brakes!" Remember, the vibration of ABS is just normalm operation!

The absolute fastest stop still happens when you are right on the verge of the wheel locking up, but not quite.
When the ABS activates it means the brakes have been applied too hard and a wheel has locked up. Thus an experienced or very careful driver may never use the antilock brake system, or at least never notice its operation.

ANTILOCK CAN HELP EVEN THE BEST DRIVERS

If a single wheel loses traction on braking, like when one wheel hits a puddle or slick spot, anti-lock can release the brakes on just that one wheel and leave the others alone. That's why the first and most high tech antilock brakes appeared in the sports car and racing industry. Close to follow were Tractor-trailer rigs: anti-lock brakes for the trailer and the rear wheels of the tractor have been common for quite some time.

ANTI-SKID SYSTEMS

Some cars now use the anti-lock brake system as a anti-skid system also: if a wheel "breaks loose", losing traction, the brakes will apply to that wheel until its speed matches the other wheels. This keeps traction on the wheel, and distributes power to the other wheel(s!) which have better grip on the road. These cars can't get stuck in the mud, with one tire still and the other one spinning, digging a hole in the dirt.

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Thank you for visiting the ECONOMECHANIX WEB SITE. Please feel free to comment. We also serve the surrounding communities of Alachua, High Springs, Hawthorne, and Newberry! Gainesville has been my home since 1974, and I've loved Gvl and the Gators since I came here in the fall of 1974 to attend the University of Florida. I loved it so much I stayed and opened my car repair business. Originally it was out of the back of a 1963 Chevrolet wagon, but in 1977 a fellow mechanic and I opened an auto repair shop with actual walls, etc. I stayed in the same location for 26 years, and recently moved my operation to property I bought 15 miles east of Gainesville. I am doing most all the repairs myself now, having reduced my overhead from $1500 per month to practically nothing. I do work by appointment only. I mostly work only on my established customers cars, but I will occasionally take on new clients. E-mail me and I will either make arrangements to look at your car, or I will recommend you to someone who will.

George G. Scott, Jr.