Anti-lock brakes/suspension on "washboard" pavement..

[birchy]

I've noticed a few times while braking on "washboard" pavement that the ABS is activating and I'm sometimes scared that I won't be able to stop in time! I know for a fact I could stop alot faster without the ABS in this case (although in icy conditions I feel the opposite).

Has anyone else had this happen? I'm starting to wonder if maybe it's more of a problem with my suspension. Since I've gotten my replacement 4Runner (original was stolen and wrecked), it seems the suspension is too stiff. In the above situation I'm thinking that the tires are probably actually 'bouncing' and causing the ABS to engage when it shouldn't. The other thing that makes me think suspension is that sometimes in this situation, when the ABS doesn't engage.. the back end on occasion will get a bit loose on me.

Any thoughts on that?

Something else I noticed.. and this is going to be hard to explain in words.. when i'm coming to a complete stop, you know how you'll be 'leaning forward' while braking.. and then when the vehicle stops you sort of 'bounce backwards' in your seat slightly. At that point, I seem to be feeling some play in the suspension I think.. almost like it's a bit lose and sort of 'clunking' back up right at the point when you stop. Is this a sign of worn suspension? Did that make ANY sense at all?

 

[techno]

I'm pretty sure I understand what your talking about, but when you say washboard pavement, what exactly do you mean? Pavement to me is a hard surface like asphalt, bitumen or concrete etc, and the washboard thing, are you talking about corrugations on gravel or dirt roads? I only ask since I never see corrugations on hard surafced roads (even here in PA!).

 

[Ron Helmuth]

you are not going crazy birchy

I think it is good you were able to describe it so well. This is an occurrence that others have noted as a shortcoming of ABS braking. Especially noticeable in deep gravel for example and slushy ice I think it is. Some people go so far as to pull their ABS fuse in winter.

I believe some studies have shown that while you are convinced you could stop in a shorter distance, the ABS will win almost every time-not every single time, but most of the time.

techno we get some washboard pavement here that I characterize as "frost heaves"- when the pavement ripples very closely together.

I think it may happen also in the hottest days of the summer. I notice it most at downhill intersections frequented by lots of semi trailer trucks. Our RTD transit buses squish the pavement here-often leaving little "waves" of asphalt-ours has a lot more give out here-not sure why...

But washboard is definitely most often found on the flattest of dirt roads with no natural ability to drain.

The back end does tend to lose traction-everyone has a theory on the best way to deal with it. I find experimenting with the correct speed is a tradeoff of speed and steering control versus bounce and jounce feel on your butt.

And I also notice the "clunk"-for me it happens on my first hard stop of the day-end of the block at the stop sign. Has not bothered me enough to mention it, and I seem unable to duplicate it for service.

 

[birchy]

Thanks Ron.

You understood exactly what I was trying to say. "Frost Heaves".. yes, I can all but guarantee thats exactly what it is.

I was talking to my uncle about it last night too because he's a pretty good mechanic. He mentioned that because these vehicles are pretty light in the rear, that the ABS engaging and the rear end getting a bit loose is pretty normal. He did suggest that I crawl underneath and check for any leaks in the shocks/struts just in case.

 

[Ron Helmuth]

makes me yearn for some washboarding now.... gotta hit some trails this weekend.

Your uncle sounds to be a wise resource-keep that guy around!