[urq] Rear 'proportion valve'

[Keith Lloyd]

I am not sure exactly how the stock one works. I thought it did not "allow" 
pressure to the rear until it experienced a certain level of force. My 
experience suggested this to me anyway.......I ltried to be mechanically 
sympathetic to my then newly rebuilt car. I was very gentle on the brakes. 
Some while later the hand brake began to have little effect. When I 
investigated I found that the handbrake/rear brakes had not been adjusting 
and the whole braking power of the car suffered. This was because I was not 
hard enough on the brake pedal to "make" the rear brakes work, so they did 
not adjust and seized up. End result - two new rear calipers. So the lesson 
I learned was to make the brakes do the braking and really stand on them. 
Sounds daft but the quattro was/is a performance car and Audi built them to 
be driven hard.

Regards
Keith

'87 WR

----- Original Message ----- 
From: "fdekat" <fdekat at sentex.net>
To: <urq at audifans.com>
Sent: Friday, November 12, 2010 9:13 AM
Subject: [urq] Rear 'proportion valve'


>
> THat 'proportion valve' that a lot have been discussing lately, in
> conjunction with Ben's brake problems:
>
> If you read the IST documents  that Martin has stashed on his web site
> (www.quattro.ca), there is a good explation as to how that valve works.
>
> It does nothing, until the rear brake circuit reaches a set pressure, then
> limits the rear circuit to that pressure.  (Also has a mechanisim to give
> rear brakes full line pressure, if front braking pressure is lost)
>
> At 'less than heavy stops', I'm thinking that it has no effect, so perhaps
> keep that in mind when doing your problem dignostics. (See chart inthe 
> IST|
> docs). Thoughts?
>
> As those 'rear line limit valves' are notorious for leaking, the Tilton 
> setup
> sounds like a good alternative.
>
> I'm curious as to exactly what that valve does or how it works?  Does it 
> just
> (adjustably) limit the rear line pressure (as the stock piece), or does it
> variably modify the rear line pressure as a percentage of the front line
> pressure?
>
>
> Regards,
>
> =Frank de Kat=
>
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