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

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I'm pretty happy with my wilwood prop valve.  Dig for my build thread on motorgeek under the name dubbinchris for pics

Chris

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On Nov 8, 2010, at 8:36, "Ben Swann" <benswann at verizon.net> wrote:

> 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
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