I thought my brakes went out, but now I still don't know what caused my accident

Question

I recently had a car accident where I gave myself a couple hundred feet to slow down before a car stopped at a red light. My car did not stop, even after pushing my brake pedal as far as I could. I initially thought that my brakes went out, but I did know that it had been raining all day and the roads were wet. I got the car checked by a mechanic and he said he could not find any problem with the brakes. Friends told me that I need to pulse the brakes next time so that will not happen. I mentioned something about pulsing the brakes to the mechanic and he said that I should not have to since the ABS should get activated. The strangest thing about the accident is that I was successfully stopped at a stop sign seconds before the accident. Even though I am driving very cautiously, the car seems to be fine now even though the brakes were not repaired in any way.

What was the most likely culprit of my accident? If I am a bad driver, I would at least like to learn what to change for the future. Do I need to pulse or tap the brakes when it is raining or wet out? Did I do the right thing by giving myself a couple hundred feet to come to a stop? Is there anything else I did not think of?

Answer 1

1. Do not EVER pulse brakes. It is an old wives' tale told by people who wish to avoid locking brakes. Pulsing brakes will rock your vehicle front and back, and that shifting of weight will hinder your vehicle's stability. Threshold braking is what you should do.
2. If you have ABS, just bury the pedal into the carpet, let the ABS do it's thing. Don't pulse, don't threshold, just hold it firm and steady. You will probably feel the pedal vibrate, that's a tell-tale sign of ABS "doing it's thing."
3. Stopping in the rain. Your brakes are wet, your tires are wet, the pavement is wet. Everything is less grippy. Whether you have ABS or not, your vehicle will take A LOT longer to stop. The best thing you can do is have tires that grip great in the conditions you are driving, give your ABS something to work with. This applies to both the "grove pattern" of your tires as well as the rubber compound used in their construction. If the outside temperature on the day of your accident was below 7-10 C, then "all-season" tires would generally be too hard at that temperature to grip properly and not have an aggressive enough grove pattern to deal with the rain.

Answer 2

Cadence braking (releasing the brakes when the wheels lock and reapplying) is an advanced driving technique which should not be required at all when using a car with ABS because that system does it for you. In an ABS equipped car simply apply as much pressure as you can to the brake pedal until the vehicle comes to a stop.

I think the clue to what happened is when you state you'd just successfully managed to stop previously. Brakes work by changing forward motion into heat. If you'd just used them it is likely that they were overheated or "cooked".

Answer 3

Assuming reasonably prudent driving and a modern car I think it is hard to believe that your brakes would have been overheated. That takes a lot of doing.

There are a couple of possibilities, that I can think of:

• "Black ice" or freezing rain. If the temperature was below freezing (or if it had been below freezing) there might have been ice on the road, even if the air had warmed up some so that it was raining.

• Hydroplaning, if the water was deep enough, and/or the tread on your tires was worn enough, the car may have been floating on a layer of water, giving the brakes very little traction.

• Oil on the road, if it had been a long time since the last rain, it is possible that enough oil residue may have accumulated on the road to make it very slippery.

• Inadequate brake boost. Since you just stopped, if you have vacuum leaks you might have not built up enough vacuum to get good brake boost.

With good tires, ABS, and even close to a reasonable road surface it is very surprising to me that you had this accident (especially since you say you'd stopped moments before, so I assume that you weren't going very fast as you approached the light). With heavy braking, I would expect the ABS to activate. If it did you may have noticed a noise and a pulsing feel in the brake pedal. If the ABS did not activate, either something is wrong with the ABS, or there weren't any of the signals that would cause it to activate (differential wheel speed).

The situation as you describe it is puzzling – you're wise to be investigating it further.

Answer 4

This probably isn't much help, but a similar thing happened several times with a '99 Cavalier. Once was after highway driving, coming to a stop on a downgrade, on wet road. The car took forever to stop. The ABS was thumping at a low rate, maybe 1 or 2 per sec. I can't swear that there wasn't a dragging disk pad or something; but, I didn't do any brake work for another two years.

The other times were on (local) snowy roads. So, overheating fluid, etc should not have been an issue. My notes don't say whether the ABS was firing or not.

I started unplugging the ABS in winter, which seemed to 'fix' the problem.