[urq] V8 Brake swap for UrQ - saga continues..

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I ended up putting a wilwood manual proportioning valve into my UrQ. The OEM prop valve was shot and I decided that any future upgrades would def need a manual valve. Pics avail of needed.

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On Nov 7, 2010, at 21:43, "Ben Swann" <benswann at verizon.net> wrote:

> Thanks for the reply - I suspected something like this.  If that is the case, then
> probably the proportioning valve won't work, except to divert all braking to the front.
> I still probably ought to install one.
> 
> There are two different master cylinders for the early UrQ.  I ordered the earlier 443
> 611 021 (23, 81X19/17) . Should I have ordered 447 611 021 (25,40X18/18) ?  I'm not sure
> what the numbers mean exactly, but presume the bore size is larger in the later version.
> Maybe there is another one I ought to get - perhaps from a different car.
> 
> I originally tried to fit the V8 Quattro Master, but it did not fit the booster - which
> prompted me to open up the booster (idiot!) thinking the plastic retainer was a spacer
> sleeve.
> 
> I could really use some help on this - I want to stay the course with the V8 brakes and
> ultimately put the Porsche monoblocks in front.
> 
> Ben
> 
>  _____  
> 
> From: Mark Rosenkrantz [mailto:speedracer.mark at gmail.com] 
> Sent: Sunday, November 07, 2010 9:14 PM
> To: Ben Swann
> Cc: urq at audifans.com; quattro at audifans.com
> Subject: Re: V8 Brake swap for UrQ - saga continues..
> 
> 
> Ben,
> 
> Without doing the calculations, I suspect you have a swept area problem. Going to
> "bigger brakes" often leaves a long pedal.
> When doing brake modifications, the size of the new caliper pistons have to be taken
> into account when choosing a brake master cylinder. With no other changes, when
> increasing piston size, often the result is a master cylinder primary piston which will
> sweep right past the correct operating area and either bottom out on the secondary
> piston, allow cross circuit hydraulics, etc. I'm tired... hardly the right term but I
> just got home after frostbiting the J-24 all day.
> Brakes are too often thought of as individual pieces and not as a system. Big mistake.
> Brembo, Stoptech, etc.... they're not taking a single caliper and making different
> brackets. The caliper bodies might be the same across different applications, but the
> piston bores sizing is application specific for, bias, area and to minimize pad taper.
> Take for example a Stoptech application for a 2000 A4 bodied car. All use the same
> caliper body, but the piston size and radio is different for a 1.8T, a 2.8, and the S4
> to match the spring rates (for bias) and master cylinder volume.
> A couple of remedies: A proportioning valve might be enough. Properly sizing the master
> cylinder. Sleeving the calipers with smaller bore pistons.
> Good luck,
> Mark Rosenkrantz
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