[s-cars] abs purge procedure

[Eric Renneisen]

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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