[s-cars] abs purge procedure

[Eric Renneisen]

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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