ABS light and Vagcom scanner

[Mark Rosenkrantz]

No proportioning valves with ABS systems on VAG cars since 1995 (That's the
last year I can think of at the moment).  GTiVR6 had one in 1995... by 1996
they were gone.  Did any of the Audis have proportioning valves past 1995?

The real safety issue is having to turn the car when braking.  Locking up
the rears in a straight line isn't such an event, but if you have to
turn/swerve with locked rear brakes, then you will start to skid.  The only
way to stop the oversteer is to release the brakes (and usually must apply
some throttle), which will surely lengthen stopping distance.  If you keep
your foot on the brake, a full spin will occur.

As an instructor, had to say it.  =)

Mark "loves to slide" Rosenkrantz

On Tue, Oct 13, 2009 at 11:51 PM, Louis-Alain Richard <larichard at plguide.com
> wrote:

> Kneale and Victor,
>
> There is a tiny little difference on newer cars. Modern ABS is a multi-task
> system, as it is now the one that do the proportioning front-rear. There is
> no hydraulic proportioning valve (dependent to the rear suspension travel)
> anymore on recent cars so the rear pressure is bled internally and quietly
> in the ABS module accordingly to the wheels speeds. Usually, ABS will
> tolerate up to 20% slower wheel at the back before the ABS pulsing could be
> felt by the driver.
>
> So Bentley is right : a non functional ABS will not release pressure on the
> rear wheels when braking hard with the nose down and the rear getting
> light.
> So braking force will be more rear-biased than in a normal braking, hence
> the warning. If your car does have a proportioning valve, then the problem
> doesn't exists.
>
> In my modest experience about this problem, it will show only at high
> speeds, and when stomping on the brakes. But that's precisely when you
> don't
> want them to lock... But it's probably no worse for safety than worn tires
> or marginally powerful brakes. Each car will behave differently, so one may
> want to test his car before concluding that it is not a safety issue.
>
> Louis-Alain
>
>
>
>
> -----Message d'origine-----
> kneale at coslink.net
>
>
> My 200q20v avant has been without ABS for two years because I mashed one of
> the sensors replacing an axle (forgot to pull it out of its socket).
> Brakes work fine except there's no ABS, which means the rears CAN lock up
> in hard braking circumstances.  Just like brakes always did before ABS.
>
>
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