[s-cars] abs purge procedure

[Theodore Chen]

the porsche caliper has two pairs of pistons opposing each other.
you don't count the opposing pistons.  if all four of them were on 
one side, then you'd add up all of their areas.

the G60 has both pistons on one side, in a sliding caliper arrangement.

-teddy

--- Mark Strangways <StrangConst at rogers.com> wrote:

> Also from a quick google, looks like...
> 996 TT uses 44mm and 36mm
> 993 use same,
> 996 and boxster use 40mm and 36mm.
> 
> Looks like the G60 uses a 57mm DIA piston and a 52mm piston... But according 
> to some web site it uses 44 and 36 mm pistons as well.
> 
> So, since the Porsche use 4 and the Girling uses 2 pistons one might 
> conclude that the area are doubled.. ?
> Is this true ? I can hardly believe that it is.
> 
> The spec seem right for the Porsche, and I dug up and measure the outside of 
> the pistons on the girlings (not prepared to open them up right now).
> 
> So, what is the case actually.
> 
> Mark ( leaving more questions on the table) S
> ----- Original Message ----- 
> From: "Eric Renneisen" <racingiron at comcast.net>
> To: "'Robert Rossato'" <bob.rossato_af at cox.net>; "'Mark Strangways'" 
> <StrangConst at rogers.com>; "'Mike Fitton'" <rfitton at vt.edu>; 
> <keith at maddock.com>
> Cc: "'S Car List'" <s-car-list at audifans.com>
> Sent: Sunday, December 17, 2006 6:50 PM
> Subject: Re: [s-cars] abs purge procedure
> 
> 
> > First, I assume we're talking piston diameter here, as fluid volume is
> > really meaningless in this context.
> >
> > I don't have the Porsche numbers handy, but virtually ALL Porsche
> > calipers anyone has put on these cars have a LOWER effective piston
> > diameter than the G60s.  The G60 piston diameters are equivalent to a
> > single-piston of 60mm (hence the name).  The 993tt, 996t, 996, Boxster
> > S, etc. all have single-piston equivalents in the mid to upper 50s.  You
> > can expect slightly less pedal travel when upgrading.  Also, I don't see
> > a good reason to go for a larger MC when you'll have less caliper piston
> > area.
> >
> > Now, as for proportioning, you've got to consider more than just piston
> > diameter.  You're also likely changing rotor diameter and pad material,
> > both of which will effect the braking force applied by a given pedal
> > force.  I'm no expert here, but I'd say do your upgrade then test (with
> > ABS disabled) to see if the balance is off.
> >
> > Eric R.
> > '86 urq - Boxster brakes (under 15" Ronals)
> > '93 urS - Stock G60s, but not for long...
> >
> > -----Original Message-----
> > From: s-car-list-bounces at audifans.com
> > [mailto:s-car-list-bounces at audifans.com] On Behalf Of Robert Rossato
> > Sent: Sunday, December 17, 2006 6:19 PM
> > To: 'Mark Strangways'; 'Mike Fitton'; keith at maddock.com
> > Cc: 'S Car List'
> > Subject: Re: [s-cars] abs purge procedure
> >
> >
> > G60s are 2 piston calipers, but you knew that so I'll assume it was just
> > a typo ;-)
> >
> > I don't know what the relative piston diameters, and depth of the piston
> > cavities, are for the G60 and 993tt calipers, but my understanding was
> > that there was a larger volume in the Porsche calipers.
> >
> >> -----Original Message-----
> >> From: s-car-list-bounces at audifans.com
> >> [mailto:s-car-list-bounces at audifans.com] On Behalf Of Mark Strangways
> >> Sent: Sunday, December 17, 2006 6:03 PM
> >> To: Mike Fitton; keith at maddock.com
> >> Cc: Robert Rossato; S Car List
> >> Subject: Re: [s-cars] abs purge procedure
> >>
> >>
> >> 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
> >
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> 
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