Re: ABS Operation, was Re: Warning Lights

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

Thanks for the info, Bernard. I wonder where the fluid goes when it is
pumped back into the MC in state (3). Does it increase the pressure on the
other brake circuits? Maybe that's the source of the pulsation in the pedal
when the ABS activates? Hmmm, I'll have to think about this some more.

Thanks again!

Fred

----- Original Message -----
From: Bernard Littau <bernardl@acumenassociates.com>
To: Fred Munro <munrof@isys.ca>; Phil Payne
<quk@isham-research.demon.co.uk>; <OorQue@aol.com>;
<Steven.Buchholz@kla-tencor.com>; <quattro@audifans.com>
Sent: Monday, October 04, 1999 1:14 AM
Subject: Re: ABS Operation, was Re: Warning Lights


> Hi Guys,
>
> I have in my hands the Audi publication: Anti-Lock Brake System,
> Introductory Information for the Audi 5000S and Audi 5000CS Turbo, printed
> 10/85.
>
> The hydraulic modulator has three states: 1) passive pass through of brake
> pressure from the master cylinder to the slave cylinders, 2) two way block
> of the movement of brake fluid, 3) return flow from slave to accumulator
to
> master cylinder via return flow pump.  The system is normally in state
(1).
> When the wheel speed sensor detects a rapid deceleration of a wheel, the
> modulator enters state (2) to prevent more pressure for reaching the
slave.
> If a wheel continues to decelerate, or has stopped, state (3) is entered
> (whereupon the wheel will start to spin), and the system enters state (1)
> again.
>
> From my reading, the operation is not dependant on the bomb, and no
mention
> of the bomb is made in the service training manual.
>
> However, as a personal note, a good bomb will reduce the pedal effort in
> both normal braking and when the ABS is engaged.  A good bomb is just a
good
> idea in an Audi.
>
> Best,
>
> Bernard Littau
> '88 5kcstq
>
> -----Original Message-----
> From: Fred Munro <munrof@isys.ca>
> To: Phil Payne <quk@isham-research.demon.co.uk>; OorQue@aol.com
> <OorQue@aol.com>; Steven.Buchholz@kla-tencor.com
> <Steven.Buchholz@kla-tencor.com>; quattro@audifans.com
> <quattro@audifans.com>
> Date: Saturday, October 02, 1999 10:35 AM
> Subject: ABS Operation, was Re: Warning Lights
>
>
> >
> >----- Original Message -----
> >From: <OorQue@aol.com>
> >To: <munrof@isys.ca>; <Steven.Buchholz@kla-tencor.com>;
> ><quattro@audifans.com>
> >Sent: Saturday, October 02, 1999 6:09 AM
> >Subject: Re: Warning Lights
> >
> >
> >> >  It takes energy to do this, and the only source of energy is the
> >hydraulic
> >> pressure in the bomb
> >>
> >> So what does that make the +12 VDC that's fed to it via the wiring
> >harness?
> >> ;^)
> >>
> >> JG
> >>
> >
> >    I didn't think the harness would supply enough 12 VDC power to drive
a
> >pump to put out the 2000 - 3000 psig required for the brake system.
> However,
> >I see there is a 10 gauge wire feeding an ABS Return Flow Pump, whatever
> >it's function is.
> >    I seem to recall a post (I think it was from Phil Payne) a while back
> >saying that activation of the ABS ate up the stored pressure in the bomb
in
> >short order, and activating the ABS with a bad bomb was bad news. As I
> >understand Steve's post, he is saying that the bomb/hydraulic boost
system
> >has nothing to do with the ABS system and a bad bomb will not affect ABS
> >operation. Is this correct?
> >Can anyone explain how the ABS modulator/ABS return flow pump/ master
> >cylinder interact?
> >
> >Fred Munro
> >'91 200q  281k km
> >
>
>