Subject: Hanging rear caliper

Bernie Benz b.benz at
Sat Apr 16 19:33:07 EDT 2005


See! If not careful one can learn something new every day.  You just made my
day!  More below.

> From: Phil Rose <pjrose at>
> Nope, it's been lurking there on your car all these years, Bernie! ;-)
> Actually this valve was something I first encountered last year when
> I needed to replace a badly corroded brakeline coming from the left
> rear caliper (return line). This brakeline goes to passenger side by
> way of a sharp u-turn into this mystery valve--the one with the big
> internal sliding weight. This valve and the plumbing are located
> about dead-center and face to the front--making it hard to access and
> not especially easy to see until you try to follow the path of the
> rear brakelines from side to side. As Chris says, the function of
> this valve is claimed to be sensing hard turns so as to prevent right
> rear wheel lock-up. Not sure why hard turns in only one direction
> were singled out for special anti-lock attention by Audi's
> overengineers.
I'll try.  The proportioning valve, intended to modulate rear braking effort
based on SRH, works only on left rear suspension input so, in a right turn
LR suspension deflection would increase the breaking pressure to both rear
wheels.  Not good for the RR wheel!  So, apparently this may be the reason
for the aadditional transverse acceleration sensitive band aid device.
Better for symmetry, IMO they should have used two proportioning valves, one
for each side of the rear suspension.

You make me crawl back under to check this out!


> Phil
>>> From: c1j1miller at
>>> -------------------
>>> There's a load sensitive proportioning valve over the left rear; then
>>> the line runs across to the right rear. Part way there it goes into a
>>> big cylinder with a moving weight that is supposed to keep the right
>>> rear from locking under a hard corner. Perhaps that is stuck?
> -- 
> Phil Rose
> Rochester, NY
> mailto:pjrose at

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