Re: ABS Operation, was Re: Warning Lights

["Bernard Littau" <bernardl@acumenassociates.com>]

Yes, that is part of the reason the pedal pulsates.  The state transitions
are the result of a plunger moving up and down, and the plunger motion will
also add to the pulsation.

HTH,

Bernard Littau
Woodinville, WA
'88 5kcstq
-----Original Message-----
From: Fred Munro <munrof@isys.ca>
To: Bernard Littau <bernardl@acumenassociates.com>
Cc: quattro@audifans.com <quattro@audifans.com>
Date: Monday, October 04, 1999 5:23 PM
Subject: Re: ABS Operation, was Re: Warning Lights


>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
>> >
>>
>>
>
>