[urq] bomb test variation with S4 brakes?

[Martin Pajak]

Steve,

I beg to differ with you.  
Increase in piston number is theory on paper.  In real life this is actually
a bit different.  There are many things to consider including how good the
callipers are (how far they retract after brake application) and how good
the sliders themselves are.

Previous car was '83 with G 60s up front and the travel was minimal.
The difference would be something your foot would not even register, not to
mention reduce # of pumps from 30 to 10!

BTW S4/V8 rear callipers use the same piston as Ur-q and in fact use the
same pads as well!!
Oh and my '85 with SQ callipers (4 piston fixed) has the shortest pedal
travel of them all.. probably because of lack of slider.

Hope this helps.

Martin Pajak

http://www.quattro.ca

1982 Audi Ur-quattro (50,000 mi) new project
1983 Audi Ur-quattro (85,000 mi) Concourse d'Elegance
1985 Audi Ur-quattro (214,000 km) Euro spec. import mit 3B :)
1987 Audi 4000s quattro (212,000 km) wintervagen mit 7A :)
 
 
-----Original Message-----
From: urq-bounces at audifans.com [mailto:urq-bounces at audifans.com] On Behalf
Of Buchholz, Steven
Sent: Monday, August 07, 2006 11:46 AM
To: urq at audifans.com
Subject: Re: [urq] bomb test variation with S4 brakes?

... beg to differ here ... pedal travel will also be altered by the piston
diameters of the brake calipers (altered by the ratio of the areas of the
surfaces upon which the pedal force is applied) ... I suspect the dual
piston G60s have more area than the G54s ... and I'm pretty sure the S4
rears have larger diameter pistons as well ... so you *should* expect more
pedal travel.

If you changed the brake M/C to compensate for the larger diameters then the
travel would be the same, but if you're running the same M/C I would not at
all be surprised to hear that you get less overall pedal applications before
losing assist.  

If the dynamic test works ... i.e. you do a panic stop and find that the
brake assist is acceptable, consistent and does not increase over time,
consider the problem solved.  When that situation changes then you should
consider a bomb replacement ... 

Steve B
San José, CA (USA)
> 
> Number of of times you can pump the brakes will only be determined by your
> pedal travel, not what brakes you have..
> If you have air in the system or spongy hoses, your pedal travel will be
> longer and number of pumps less.. however I can not see how that number
> can be reduced to 10 if you have properly functioning brakes.
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