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Re: Quattro Digest V1 #376

>In a parking lot he happen to be driving with the right side 
>of the truck on glare ice and the left side of the truck on bare pavement. 
>He says he applied the brakes and the pedal was 'wooden', no matter how 
>hard he pushed he got not brakes whatsoever.  The scared him greatly, as it 
>was only luck that no one was crossing the intersection he went through.  He

>went back and tried it the otherway, left on ice , right on pavement and the

>ABS operated just fine.

Sounds like maybe some or all of the wheels on one side of the car (left or
right) are on the same ABS channel(s) as wheels on the other side which would
explain the braking problem.  Most 2 or 3 channel ABS systems are laid out
this way so that if one wheel on a channel starts to lock, braking to all
wheels on the same channel is reduced to prevent lockup.  Though, if that
were the case, braking would be a problem in both instances of either having
the left or right side on ice.  It would help to know how many channels of
ABS were on the Explorer and whether it was in 4WD mode (4WD or AWD reduces
or eliminates the tendency of the front and rear axles from locking up
independently).  Faulty ABS sensors on one or more wheels might explain the
problem, though I would hope that manufacturers would have some sort of
warning for cases like that.

I drive a Mitsubishi Galant VR-4 that has a 2 channel ABS system where the
wheels diagonal to each other on the car are on the same channel.  In the
case of ice on just the left or right side of the car I should have a similar
problem slowing down (haven't been in that situation yet).

><switch off the ABS when there is snow on the ground???
> Call me crazy, but isn't that what ABS is for?  Low traction situations are
> what all of the manufacturers are claiming is THE place that people NEED

The exception with ABS and  deep snow is that you can reduce braking distance
in snow by locking up the brakes.  The snow piles up in front of the locked
up tires and helps slow the car down (works on gravel also).  Of course with
the tires locked up you won't be able to steer and could go into a spin so
it's a trade-off.

I'm new to this list so I don't know if this has been mentioned before but
there's a great book available:  All-Wheel-Drive High Performance Handbook by
Jay Lamm available from Classic Motorbooks (800) 826-6600.  It covers the
basic concepts of AWD cars and has a nice history of Audi in racing.