V8 Brake swap for UrQ - saga continues..

[Ben Swann]

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.
 
So., 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.  That was the reason I molested the
master and booster in the first place.
 
Main reason for this post: Recommendations for adustable proportioning valve and any
installation advice.  
 
Am I on the right track with this?   I will replace the rear lines, maybe front lines
too.  So system will have new master, adjustable proportioning valve, V8 rear brake
setup.  Presently the fronts are the dual caliper brakes from an '87 5000 turbo quattro.
Except for the left rear caliper dragging and locking up  before all the work, the
brakes worked great.  I had already swapped the rear calipers out too for the newer
style which lasted several years.
 
I have the option to install PORSCHE Monoblock calipers too - like I want to make more
changes, but being I'm changing ther rears, master and proportioning valve, maybe time
for these I've had on the shelf for sometime.
 
So looking for advice on the proportioning valve as well as anything else that will keep
me from digging this hole any deeper.  I have not ruled out booster problem, but no
reason to suspect that - new booster, relatively new bomb, new bomb to rack hose, no
leaks!
 
I recall having a similar, if not identical problem on an '83 CGT that I did the MC-1
turbo install.  I had pretty much installed "retro" brakes all-around. converted rears
to disk and fronts to larger model 80 brakes.  I never was able to get those brakes
right.  Same thing - spongy pedal, reduced braking, followed by pedal going to the
floor.
 
Ben


  _____  

From: Ben Swann [mailto:benswann at verizon.net] 
Sent: Saturday, September 18, 2010 12:47 AM
To: urq at audifans.com
Cc: benswann at verizon.net
Subject: V8 Brake swap for UrQ - bad info worse than no info.?

I have been in process of upgrading rear brakes to V8 calipers, carriers and rotors.
That part went fairly well and except for having a little mixup with the rotors - that
looks great!

There were several "suggestions" from folks I put high credibility in information I get
on this list -  that in order to utilize the larger diameter rears I needed to also use
the V8 or 200 master cyl.  Good suggestion I thought - pretty trivial to replace that -
albiet a bit or a PITA.    One ought to presume that unless additional information is
given to the contrary that a swap is a simple swap.

Now this is where someone should have provided a clue that this was not a doable swap
for mere mortals or at least there was more to just swapping the master cylinder out.
If there was BTDT on this I should have been advised
.

OK - The line hookup needed to bend the lines  and reconfigure the hookups - old MC had
lines   on bottom and sides - new MC had a V configuration. That is not t a real big
deal, but should have been mentioned.  Not everyone presumes things need to be bent or
... 

  [ SNIP ] 

Ben