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

[qshipq at aol.com]

 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


 

 

-----Original Message-----
From: Ben Swann <benswann at verizon.net>
To: 'Ben Swann' <benswann at verizon.net>; urq at audifans.com
Cc: quattro at audifans.com
Sent: Sun, Nov 7, 2010 7:08 pm
Subject: [urq] 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.

 

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