I had heard and seen something strange on a Chevy ABS system once.
When you hit the brakes, the rear wheels would lock, then spin the
opposite direction! This was only the case on the Blazers and
S-trucks. I saw it once in snow and couldn't imagine how it would
be possible. If I didn't see it with my own eyes, I wouldn't have
believed it either. Of course, the vehicle was moving in reverse,
but that shouldn't make a difference.
Did I mention this was on the same vehicles that had the ABS recall?
Yep, my Mom's blazer. The same one that lost pedal pressure, only
to have it back a second later. Not a welcome feeling when trying
to stop.
Mike Lishego
http://www.mgb.bc.ca/virtualgarage/
1991 Mazda Miata
1986 Plymouth Turismo T1
1984 Mazda RX-7 GSL-SE
1974 MGB
Asheboro, North Carolina
-----Original Message-----
From: Larry Dickstein <bugide@tfs.net>
To: Steve Shoyer <Steve@shoyer.com>
Cc: 'mgs@autox.team.net' <mgs@autox.team.net>
Date: Friday, January 14, 2000 6:18 PM
Subject: Re: FW: Speeding in the UK (ABS)
>Steve Shoyer wrote:
>
>> The way it's been explained to me, if you lock up the wheels when
stopping
>> on snow/sand/gravel, a wedge of snow/sand/gravel is created in
front of the
>> tire from being pushed, which helps to stop the car. With ABS,
because the
>> wheel never locks up, it continues to roll over the
snow/sand/gravel, the
>> build-up doesn't happen, so the car doesn't have that additional
friction to
>> slow it down. Something like that.
>>
>> --Steve
>
> Not completely true, Steve. What normally happens when the
brakes of a
>non-ABS vehicle lock is that the rear wheels lock first and the
vehicle tends to
>swap ends-dry pavement or ice-it doesn't matter. When that happens
the benefit
>of added friction is negligible and there was very little friction
to begin with
>since the tire is now riding on a thin layer of melted rubber.
Figuring dry,
>worn concrete has a coeffiecient of friction of 60-75 % on a good
day, adding
>sand, gravel, or snow only reduces the coeffiecient of friction.
Conversely,
>adding sand or cinders to a roadway covered w/ glaze ice (COF of
10-15%) can
>only increase the friction because there was precious little to
begin with.
> Now if the sand or gravel were deep enough like a truck runaway
ramp in the
>mountains, then whomever told you about sand and gravel would be
right. The
>vehicle sinks into the aggragate far deeper than sliding along w/
the material
>only building a little and then coming out from around the tire.
> You are right about the ABS vehicle not building up the
additional
>friction. The plan is to maximize the braking power w/out locking
up the tires,
>as you note. Some folks think the ABS works like "pumping the
brakes" (am I
>dating myself?) but it does not let the brakes ever lock but
releases pressure
>on the brake just short of locking.
> I had a '71 Lincoln Continental Mk III in the early 70's. It
was equipped
>w/ a Kelsey-Hayes setup that was a fairly primative anti lock brake
system for
>the rear tires. It made one heck of a racket when it activated but
one could
>not lock the rear brakes. The idea is not as new as some might
think.
> Obligatory MG content: tomorrow is supposed to be 60 and fair
around here.
>It might be a good day to spend some time on the V8 project!
>
>
>--
>Larry Dickstein
>Lone Jack, MO
>
>
>
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