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

[Ben Swann]

From: Ben Swann [mailto:benswann at verizon.net] 
Sent: Monday, November 08, 2010 7:41 AM
To: urq at audifans.com
Cc: quattro at audifans.com; 'Mark Rosenkrantz'; qshipq at aol.com; 'Ben Swann'
Subject: RE: V8 Brake swap for UrQ - saga continues..

I ordered the later version of the MC anyway - I can return or shelve whichever I don't
use.  I think that the earlier is 23mm bore and later 25mm.  I'm not sure what the
second set of numbers mean: The two versions are described in ETKA as earlier 443 611
021 (23, 81X19/17) vs.  later 447 611 021 (25,40X18/18).
 
At least I'll have both on hand.  It certainly does feel like a bad master cylinder.
 
I'd like to order an adjustable proportioning valve today, so any more recommendations
on that?
 
Ben
[From: qshipq at aol.com [mailto:qshipq at aol.com] 
Sent: Sunday, November 07, 2010 11:23 PM
To: benswann at verizon.net; urq at audifans.com
Subject: Re: [urq] V8 Brake swap for UrQ - saga continues..

Sounds like a bad master or bomb to me, or air/leak in the system  I've installed a
couple dozen v8 rear brake setups on urq's over the years, with a wide variety in front
from G60 and to Big Reds....  Most with the stock urq 23mm MC.  I routinely replace the
prop valve with the Tilton 7 position adjustable, and normally set it almost full front,
except when at the track, and/or locking the center diff.  For the G60 brake setup with
'v8' rears, you can use the euro 20vt stock brake prop valve, as the G60F/v8R setup came
on that car from the factory.


IMO, what you describe has nothing to do with the size of the rear brakes or the prop
valve (36/38mm stock to 41/43mm v8 rear piston dia should yield little to no difference
in pedal travel).  The stock MC can handle several different caliper setups with no
significant difference in pedal travel, btdt.  Certainly if the pedal goes to the floor,
one can be assured there is another problem.  IME with every audi hydraulic brake setup
that exhibits this issue, I first go to the MC, then to the brake bomb.

Scott J
Stock urq MC'd
84 urq Big Reds Front/V8 R Tilton-7
83 urq Steamboat car G60F/V8R Tilton-7
Sold
83 urq G60 F/v8R 
83 urq G60F/v8R
83 urq G60F/v8R]
[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][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]
From: Ben Swann [mailto:benswann at verizon.net] 
Sent: Sunday, November 07, 2010 8:09 PM
To: 'Ben Swann'; urq at audifans.com
Cc: quattro at audifans.com
Subject: V8 Brake swap for UrQ - saga continues..

The Brake saga continues on my '83 Ur Quattro.  I finally have a replacement booster
installed to replace the one I botched.
 
To recap., I installed V8 brakes in the rear and messed up the original hydraulic
booster when trying to retrofit a V8 master cylinder.  That in order to proivde correct
brake proportioning/compensating for the newly installed rear V8 calipers.
 
After repetitively bleeding the system - I now think there is another problem or two.  I
am fairly certain I have the air out of the lines, Master cyinder and slave cylinders.
I have gone through no less than 4 full liter containers of DOT 4 in several attempts to
remove the soft pedal.  Even though I got some air out in repeated attempts using power
bleeding and manual ( foot and other techniques), the brakes still do not work.  Seems
no matter what I do, I still have the same end result - spongy pedal that provides
little braking and continues to the floor with moderate pressure.
 
I ordered a master cylinder since the pedal  is not only spongy, but continues to go all
the way to the floor when held.  The pedal can be pumped hard, but shortly after the
slight braking, the pedal goes down, and then again until it bottoms out.  Braking is
almost non-existant, although will skid in rear  or lock up sometimes when near bottom
of pedel travel.
I think I need to replace the proportioning valve, and should do it with the new master,
since I need to crack the system again.  I was going to get a stock proportioning valve,
but since I changed the calipers, part of the problem may be that I need to adjust the
bias for the rear V8 calipers.  
Main reason for this post: Recommendations for adustable proportioning valve and any
installation advice.  
 
Am I on the right track with this?  [Snip]
Ben