[s-cars] abs purge procedure

[Mark Strangways]

I don't actually think the Porsche calipers are have any less fluid then the 
G60's.
Remember that the Porsche are 4 piston and the g 60 is 1 piston.

The proportioning valve works on pressure principals not flow.
You may find that if the front NEW calipers contain less volume than the OLD 
calipers, you will get a firmer pedal due to the higher force required to 
exert the same pressure and you will also find that they react faster.
The reverse would be true for the rears if the NEW calipers where large 
volume.

Either way I don't expect you will have any problems.

As Robert beat me to it... you will find there is a ton of pedal firmness to 
be had by servicing and adjusting the rear calipers properly. Many factors 
can lead to the pads being way to far away from the rotors, this adds the 
need for more fluid volume to the caliper before it starts to build force.

Mark
----- Original Message ----- 
From: "Mike Fitton" <rfitton at vt.edu>
To: <keith at maddock.com>
Cc: "Robert Rossato" <bob.rossato_af at cox.net>; "S Car List" 
<s-car-list at audifans.com>
Sent: Sunday, December 17, 2006 5:43 PM
Subject: Re: [s-cars] abs purge procedure


> Interesting.  I've never looked closely at the rears, but I was halfway
> thinking about going the A8 caliper route just for the weight savings.
> That would mean new components pretty much everywhere.
>
> Something I'm concerned about...the Porsche calipers I'm betting have a
> lot less fluid capacity than the G60s they're replacing.  The A8 rear's
> piston I've also heard is slightly bigger than stock.  Less capacity in
> the front, more capacity in the rear.  I see trouble brewing.  Any
> chance the stock prop valve is adjustable?  Any thoughts?
>
> -Cheers!
> Mike
>
> Keith Maddock wrote:
>> Mike, Bob:
>>
>> I was talking to one of our foundation brake engineers the other day
>> who also has a 95.5 S6, after he drove mine.   We started talking
>> about the stock brakes and the Porsche upgrade options.
>>
>> It was interesting to hear him counter my comments that the G60's were
>> very flexible.  The idea offered was that the G60's tend to wear the
>> pads/rotors in a slightly uneven fashion - which causes more pad
>> "kickback" than normal.  This results in increased pedal travel as you
>> have to move the pistons that much further before you actually start
>> getting clamping.
>>
>> Anyway - this would support Bob's suggestion that new pads/rotors
>> would firm things up.
>>
>> Cheers,
>> Keith
>>
>> On 12/17/06, Robert Rossato <bob.rossato_af at cox.net> wrote:
>>> Well, as we all know the North American models of the UrS4/6 have fairly
>>> soft brakes to begin with.  However, one thing I've noticed that will
>>> dramatically improve the feel of the brakes is new rear rotors and pads.
>>> What shape are your rear brakes in?  Even if they have a decent amount
>>> of pad material left, they will feel much better with new pads & rotors.
>>> For whatever reason they definitely do not stay firm throughout their
>>> pad life.  It may be due to corrosion build-up on the caliper carrier
>>> where the pads slide.  It might have a tendency to push the pads back
>>> when they're thinner.  I always wire brush that area to get rid of all
>>> scale and add a little anti-seize.
>>>
>>> And then of course there is the flexure of the front G60s, which it
>>> sounds like you're already planning on replacing.
>>>
>>> bob
>>
>
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