Just after reading some of the debate on a recent/current ABS thread, I went
out and jumped on my brakes on a wet road with a slight curve. (I won't say
whether it was planned or not.)
The anti lock system activated, and I came to a controlled stop.
Let's just say it was exciting.
Now my question: The pedal feeling and sounds are so rapid and violent,
like a small machine gun, that I can't help but think that it's wearing
something out pretty rapidly. Is it?
The modulator valves? The hydraulic brake line fittings? Nothing?
Congradulations. Now you know what abs feels like. I agree with your
assessment that it sounds like some damage is occuring, but I assure you, none
is. Perhaps someone with more mechanical knowledge than I can explain it
better, but in short what is happening is, you activate the brake and pump
fluid to the pads causing them to grip the disc to stop. The sensors detect
approaching lock-up and briefly release the hydraulics. What you are feeling
and hearing is this release. The first abs brakes where worse than today's,
giving you much kick-back through the brake pedal, and rachet noise from the
brakes. But, nothing is being damaged.
What you experienced is what *everyone* does when they *use* the abs. It is
far better to experience this in a non-emergency condition, because your first
inclination is to lift from the pedal.
Whenever I rent a car (usually on fishing trips) I immediately find out whether
it has abs, either by asking the agent, or check the panel at start-up. If I
am still unsure, I will put the right side in some dirt and jump on the brakes.
It's important to know this because the operation of non-abs is exactly
opposite of what you do *with* abs.
And most important - remember to steer!
It's not aproaching lock-up, it's lock-up! That's what you hear on a dry
road and you'll even leave marks on the road which the cops use to determine
your initial speed.
Well, one out of two isn't bad, Ronald. I'll go along with your "lock-up" but
most abs experts use the term "approaching lock-up". It locks-up for the
shortest of time (milliseconds?). The tire tracks you see in the road are not
caused by the abs at lock-up. Otherwise you would see tire marks once on every
revolution the same as you would see if the tire was on grass or dirt.
Ok, this is sort of funny now.
I have known (through inattentive driving and such) what ABS feels like for
years now. It's also caused me to have no illusions of my personally being
able to out perform it - especially while steering. I most likely can not
without the proper training, practice, and road conditions.
After yesterday's event, I am just now wondering (new thread) what the weak
point in the mechanical system might be, regarding wear.
In other words, if I want to practice max stopping/steering maneuvers within
slick or snowy parking lots, am I wearing anything out aside from my brake
pads and rotors?
The answer seems to be "no", but it was worth asking.
I'm one of the converted, believe me.
You are causing wear, of course, but you are not hurting anything. The wear
would be on the pads and the rotor. The school cars (Ford Taurus) take a big
beating each day they are used, but brakes last a long time, even under school
I don't believe *any* human being is capable of out-performing a decent
The one obvious wear issue is the tyres themselves (tires for our US
cousins :) I doubt a full bore ABS assisted stop from high speed does
much good to your tyres at all, but then this is relative. Compared to
a long skid on totally locked wheels, the tyre wear is obviously less
and distributed around the circumference of the tyre rather than in a
single spot, but there's obviously more wear involved than if ABS were
never invoked in the first place.
Then I believe that you should re-read the comments, take any additional
training that (may) be required, and prove yourself wrong.
Tyre wear should be fairly neutral, I'd have thought. Locking the wheels
would induce more wear (the phrase "flat-spot" ring a bell? ;o)
The number of flat-spots that an ABS system would induce is - IMHO - a very
minor amount of wear in the overall wear-pattern of a tyre, assuming
"normal" usage and material. I think that we agree on that one! :o)
Yeah, what he says. I know lots of drivers that can beat abs. It is nothing
more than training. At a school teaching teens defensive driving in Vermont,
after a lane change exercise using abs, we turned off the abs and did it the
old way with threshold braking. My first student did it perfectly at 45 mph.
I upped the speed to 55 and again he did it as well as anyone I've ever
observed using threshold braking. This kid was 18 and he was good. We
normally didn't go above 55 without abs, but he was so good I took him through
at 60. Again, perfect.
We questioned him later and found out that he lived on a farm and drove the
school bus. His farm was on a hill and at the bottom was a stopsign: you had
to turn left or right or go into a river. He taught himself threshold braking
on that hill in the worst of weather.
Although when the wheels actually lock-up, they obviously have to slow
down to zero rotational speed, I believe this slow down happens so
quickly that not even the fastest ABS system is actually capable of
detecting the rapid speed drop and releasing the calipers in time to
stop it. Basically by the time the calipers are released, the wheel has
already stopped rotating. Obviously the faster the system reacts, the
less time the wheels will spend "stopped", but no system can stop it
Actually, I think you're incorrect. I know that the engineers decide
*how much* rotational difference is tolerated before the ABS is
engaged. BMW used "25%", last time I'd heard anything in particular.
Now what *that* means I'm not quite sure. We didn't ask for enough of
an explanation to completely understand it. Any *more* anal retentive
engineer/trivia freaks out there?
(Been there; done that)
If you drove like that all the time, you'd wear out your brakes :-)
Seriously, though, although the ABS is only designed for emergencies to
prevent skidding, the quattro system uses the same components and is very
reliable even in continuous winter use.
It (should!) be designed to take the load.
Arguably there is potentially more damage to the surface of the pads (the
on/off is arguably more violent and frequent than a typical human driver
would apply), but - IMHO - I would very, very much doubt that it has a
significant difference on the service interval for the pads.
Theoretically, depending upon the materials used, it could shorten the life
of the calliper seals. Mind you, they should have failed any rational
test/inspection w-a-y before then.
Hairy One Kenobi
Disclaimer: the opinions expressed in this opinion do not necessarily
On Fri, 12 Dec 2003 01:15:22 -0000, "Hairy One Kenobi"
I politely disagree.
The actual travel of the calipers when the ABS opens and re-applies
brake pressure is IMO a few hundreds of a Millimeter. The pressure on
the pad's fluctuates, but for that not a lot of travel is needed
anyway. This travel is IMO covered in the flexibility of the seals
itself, there's not much real relative movement there. If you look at
it the travel of the calipers is mostly caused by the wear of the
pads, making them thinner and the calipers moving out.
I think the ABS control valve and the tubes running to the wheels will
vibrate but I haven't heard or read about mechanical damages to these
* Audi A6 Avant TDI *
* reply to wolfgang dot pawlinetz at chello dot at *
I'm thinking crack propagation. That said, I would reverently hope that the
callipers had been overhauled w-a-y before then..
The pipes should be OK, as long as they're not copper (work hardening)
Respectfully disagreeing, IME, there's always enough hydraulic pressure to
push the pistons *out* and very little in terms of piston seal flex to bring
them *back*. That's why the simplest visual indicator of a stuck piston is
excessively worn pads on that wheel.
(Been there; broke that)
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