Re: Warning Lights

["Fred Munro" <munrof@isys.ca>]

----- Original Message -----
From: Buchholz, Steven <Steven.Buchholz@kla-tencor.com>
To: 'qlist' <quattro@audifans.com>
Sent: Thursday, September 30, 1999 1:54 PM
Subject: RE: Warning Lights


> >     I can bet that your ABS did not engage, because without a
> > bomb full of
> > pressurized fluid, there is nothing to power the ABS system!
> > From what I
> > understand, when the ABS activated, it uses up a lot of
> > pressure in a hurry,
> > and without a charged bomb the pump can't keep up to the demand.
>

Then Steven Buchholz said:

> No ... the ABS system has its own pump ... it makes no assumptions about
the
> steering/brake assist hydraulic system.  If you think about it the working
> fluid that the ABS system operates in is the DOT-3/4 brake fluid, not the
> ATF/Pentosin fluid that the "bomb" deals with.
>
[snip]

Are you absolutely sure about this, Steven? I think what you are calling the
ABS pump is the ABS hydraulic modulator. It receives signals from the ABS
computer and releases hydraulic pressure on individual calipers to release
the brake if the wheel slows too fast. When activated, the ABS system
rapidly clamps and unclamps calipers. It takes energy to do this, and the
only source of energy is the hydraulic pressure in the bomb, which is fed to
the brake system ( the DOT 4 working fluid as you put it) via the brake
servo. Your foot has only pumped the pedal once and at this point is
probably trying to push it through the firewall.
    I'm not an expert on the ABS system, but this is the way I see it
working. Any comments from other listers?

Fred Munro
'91 200q  281k km