Doug

I think this is just normal ABS, but it was a little freaky, so I thought I'd post.

I was coming into downtown Seattle on I-5, which has a rather pitted road surface, due to the use of studded tires here in WA. There was light rain and the pavement was fully wetted. Traffic was slowing down and the truck in front of me, I found out, had no brake lights.

I hit the brakes just as I passed over a metal expansion joint and there was no breaking action for about .25 to .5 seconds, then the started pedal pulsing as the car began to slow, but braking performance seemed slow. Once safe, I then let up on the pedal, braking action improved, and the pulsing stopped.

I've never had an ABS car before, so I'm just guessing that the braking was poor due to the wheels locking up on the expansion joint at low pedal pressure. ls this normal ABS functioning. Any comments?

Doug

CraigB

Sounds normal. You can do it in the dry, if you stand on the brakes hard enough.

mm

This is normal ABS behavior. When the ABS activates, the brake pedal will pulse under your foot. In conditions where you want the maximum braking possible with an ABS equipped car, DO NOT release of let up on the brake pedal when you feel the ABS pulsation. Doing so will reduce the amount of braking force, which is of course not what you want for maximum braking. The pulsing you feel in the pedal is actually the ABS system modulating the brakes to prevent wheel lockup and provide maximum braking. ABS will generally allow your car to stop in the shortest possible distance and will also allow you to maintain maximum steering control while braking.

In an emergency stopping situation where you need to stop as quickly as possible with ABS to avoid a collision, remember the following rules:

STOMP on the brake pedal hard even though it may pulsate,
STAY on the brake pedal even though it may pulsate,
STEER around any obstacles as best you can while keeping your foot firmly on the brake pedal for maximum braking.

Many people end up getting into accidents because they are not familiar with the ABS pulsation and actually release the brakes when they feel it, causing their stopping distances to be greatly increased and often resulting in an unnecessary collision. If you have never driven an ABS equipped car very much before, you should familiarize yourself with how the system works and feels. The next time it rains or is slick out, go to a large empty parking lot and practice ABS braking and also steering while ABS braking. The more familiar you are with how ABS reacts and feels, the better you will be able to avoid an accident in an emergency situation on the road.

Also note that tests have found that while ABS generally yields the shortest stopping distances on most driving surfaces, on some loose surfaces, such as gravel or snow, ABS may actually increase stopping distances somewhat, although it will allow you to maintain better steering control while braking. The increased stopping distances on loose surfaces result in situations where the quickest stops can actually be accomplished by locking up the wheels, which ABS (i.e. Anti-Lock Brake System) obviously prevents. However, ABS does at least allow for greater steering control which would could be as well achieved when braking with locked wheels.

Generally ABS is a good thing IF the driver knows what to expect and how to use it. Educate yourself, know your car, learn how your car responds in different situations, and drive safely.

Peace!

Doug

... that braking performance improved when I let up on pedal pressure and ABS kicked out. Guess I just need to experiment with it more.

Doug