[urq] bomb test variation with S4 brakes?

[Schaible, David]

This sounds like the most accurate analysis so far....i believe the
pedal travel difference should not be big unless there is still air.
Last time I rebuilt my fronts (g54) I had to bleed three times, with a
power bleeder till  the feel was good.  I have the original mc but may
switch to the 5k mc one that my friend has on his which gives better
bias to the rears.....i lock up the fronts way to easy.  

However, the rear tires have been taking a beating from ebraking which
seems to me to take way too much effort on tarmac. I was wondering if
there is a better lever system which would require less torque to lock
the rears.




-----Original Message-----
From: Renneisen, Eric 475 [mailto:Eric.Renneisen at CIGNA.com] 
Sent: Tuesday, August 08, 2006 10:39 AM
To: urq at audifans.com
Subject: [urq] bomb test variation with S4 brakes?

Martin wrote:
> Show of hands to all who have done G60 upgrade (or 4 piston
callipers), 
> did not change MC and still have great brakes (i.e. very little pedal
travel)??

I don't really consider minor variations in pedal travel to be
indicative of the 
quality of braking--consistency and modulation are far more important.
That 
said, both my '85 and current '86 had G60s and stock MC when I got them.

The brakes worked fine (not "great"), but the pedal travel WAS slightly
longer.  
This makes sense because the G60 calipers have an effective piston
diameter 
(equivalent single piston) of 60mm, hence the name.  Similarly, the
stock urq 
caliper (G54) is 54mm.

Currently, I'm running Boxster 4-piston calipers.  My calculations show
that 
the effective single-piston diameter of these is 53.8mm, very close to
the 
stock 54mm.  My pedal travel is noticeably shorter than with the G60s, 
which makes heel & toe action MUCH easier.  In this respect, pedal
travel 
does directly impact my opinion of brake quality.

FYI, even the Porsche 993t (big reds) and 996t calipers have an
effective 
single piston diameter of about 57mm, proving yet again that it's not
the size 
that counts, it's how you use it.  ;^)

Eric R.
'86 urq
'93 S4

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