[s-cars] abs purge procedure

Mon Dec 18 17:37:30 EST 2006

I wouldn't say here in this discussion that volume is irrelevant.

Yes the G60 has a slightly larger effective piston diameter than the
Big Reds, so it will use more fluid for that reason.   Also, the G60
is more flexible (a little or a lot, debatable), so that also means
more fluid is used.  Additionally as previously mentioned, the G60 has
a worse knockback problem which also means more fluid is used - this
all means more pedal travel for the same deceleration, which
translates for most into poorer pedal feel.  (the original trigger of
this discussion!)

The reduced piston area of the big reds is made up for the fact that
they're always paired with a larger rotor size.  So the raw braking
power is equal or slightly higher.  The math can be done but my brain
hurts, so I'm not doing it ;)  The end result is that the big red
upgrades don't afffect the front-rear brake balance that much.  From
my experience in the 93 S4 with ECS stage 2, the rears still felt a
bit overbraked, when braking heavily for corners (I remember really
noticing this at Gingerman but other tracks too along the way of 2002
One Lap of America).  Maybe my heigh sensing prop valve was stuck on
max rear bias, who knows.  Because of this I always recommend leaving
the rear pads stock even if running track pads in the front.

The G60's and stock rotors don't have any problem stopping the car,
once.  The benefit of the Big Reds (with larger rotors) is better
repeated stopping performance (resistance to brake fade) and most find
a slightly better pedal feel as well.  Another benefit is reduced
unsprung weight.   Oh and it looks cool :-D

Cheers,
Keith

On 12/18/06, Eric Renneisen <racingiron at comcast.net> wrote:
> Your numbers for the Porsche calipers are correct, but not the G60.  I
> just measured one and came up with 45 and 40 mm.  That works out to
> about 60.2 mm as a single piston.
>
> Eric R.
> '86 urq
> '93 urS
>
> -----Original Message-----
> From: Mark Strangways [mailto:StrangConst at rogers.com]
> Sent: Sunday, December 17, 2006 8:25 PM
> To: Eric Renneisen; 'Robert Rossato'; 'Mike Fitton'; keith at maddock.com
> Cc: 'S Car List'
> Subject: Re: [s-cars] abs purge procedure
>
>
> So then all else being equal, the calipers have the same effective
> piston
> area then ?
>
> Still not 100% sure that the Girlings are 44 and 36mm .
>
> Mark
> ----- Original Message -----
> From: "Eric Renneisen" <racingiron at comcast.net>
> To: "'Mark Strangways'" <StrangConst at rogers.com>; "'Robert Rossato'"
> <bob.rossato_af at cox.net>; "'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 8:16 PM
> Subject: Re: [s-cars] abs purge procedure
>
>
> > The opposed design of the Porsche calipers means that you only count
> > the pistons on one side when comparing to a sliding caliper, like the
> > G60.
> >
> > Eric R.
> > '86 urq
> > '93 urS
> >
> > -----Original Message-----
> > From: Mark Strangways [mailto:StrangConst at rogers.com]
> > Sent: Sunday, December 17, 2006 7:46 PM
> > To: Eric Renneisen; 'Robert Rossato'; 'Mike Fitton'; keith at maddock.com
> > Cc: 'S Car List'
> > Subject: Re: [s-cars] abs purge procedure
> >
> >
> > 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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