scary ABS action tonight

[JasonF]

I was out driving tonight and it was about 36 degrees out. The roads were wet but not what i would call icy, maybe slightly slick. I came up to a stop sign where they hadn't plowed over far enough to the right so I decided to try my ABS out and see what it would do if the right side was in the snow and the left sides were on the wet pavement. I expected to feel the ABS come on on the right but still stop in about the same distance since my left tires were on pavement. Boy was I wrong! Felt major ABS humming and really laid into the pedal, but I continued to roll for the duration of the snow, went past the stop sign and then finally stopped quick once I was back to pavement under both front tires. Needless to say I was quite surprised that the system was not able to take advantage of the grip on the left side to stop me faster. I can somewhat understand it not braking harder on the left to keep the truck from pulling to the left, but hell I would rather have it pull to the left a little bit and stop than just keep on going! Is this typical of ABS or is there more to the story?

Jason

 

[dejello]

ABS keeps your tires from locking up and skidding.. Gives you the control to swerve if you need to (Someone correct me if I'm off).. Scared the living crap out of me when it first happened to me because I wasn't trying, and didn't need to swerve..

About a week after I got my Ex, I was turning off a highway like I always did in my previous vehicle without ABS (And yes, it was a lighter car, easier to stop)... Well, I just kept on going and went off the road... Now I'm used to it, but it acts up sometimes...

I don't know about your specific experience though (or setup - I only have rear ABS), mine was warm weather, dry roads..

 

[ldspartan]

Assuming your brakes are powerful enough to lock up the wheels (which they generally are, as thats the reason ABS exists), then the distance you can stop in is defined by how much friction your tires have with the ground. Since you had half your tires on snow, you stopping distance considerably. All the ABS does is allow you to stop as fast as possible without locking up a wheel.

Some Xs (at least mine, a 98) have 4 channel ABS, meaning that individual brakes get pulsed just the amount they need to in order to keep that particular tire from locking up; older cars (the 95 taurus I used to have, for instance) had 1 channel ABS that would pulse all the brakes together. A 1 channel system would show an increased stopping distance (especially in the situation you described) over a 4 channel system.

Hope that clears things up a bit.

--
Phil

 

[boominXplorer]

My ABS light is always on and all of the bakes work but they lock up. They seen to work better then just the regular ABS. Expecially offroad whe the tires are spinning!

 

[JasonF]

Phil, I agree with what you said, but I was under the impression that my truck had 4 channel ABS. However, I am not 100% positive about this. What I do know is I could have easily stopped in a shorter distance in a non-ABS vehicle in the situation I described. I can only imagine how many accidents people must have had when they relied on ABS and this is what happens

 

[Robert]

My '97 uses 3-channel ABS. I know for a fact the '95 & '96 also do. I am about 90% certain that the '98-'00 Explorers do as well. There is one rear ABS sensor. It is mounted on the top of the differential. Since Ford went to using the RABS sensor as the vehicle speed sensor in '98, that says to me that the rear is still only a single channel. Unless your rear wheels have a sensor for each wheel like the fronts do, you only have 3-channel ABS. I haven't seen any Explorer with individual ABS sensors on the rear wheels, but I haven't exactly been looking for them though.

JasonF - Since yours is only a 3-channel system, you only had one tire that could provide maximum braking once you got the one side in the snow. Your left rear tire's braking efficiency would be limited by the traction to your right tire (which was almost zero). Your right front tire was also almost zero. You really only had one tire that could brake at its maximum efficiency. This is one of the downsides to 3-channel ABS. The upside is that is is cheaper to manufacture.

 

[JasonF]

Thanks Robert, that sounds correct. Knowing this I will take it under advisory that if I ever have to make a panic stop, I will NOT lay into the pedal as hard as I can (like they tell you) and rely on the the ABS to do its job. Instead I will try and do maximum braking like in a conventional car and be just shy of the point of locking them up.

Jason