[s-cars] abs purge procedure

[Eric Renneisen]

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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