Loss of Braking power on 100CSQ Avant

[David Torrey]

Todd -

I think you may have solved this one.  I couldn't find much in the way of
failed vacuum boosters in the archives for this model.  Your theory of the
rear brakes not working sounds very plausible.  My emergency brake does
work, but I can only raise the handle 2 - 3 inches.  I just took a peek at
the rear rotors and they have ridges on the braking surface.  The front
rotors are smooth.

Does this mean my calipers are probably seized?  Or, rather the carrier that
slides on the pins to be more exact.  I assume the caliper and pistons are
still ok.  Perhaps the pistons in the caliper are not working either. I
won't know for sure until I try and take them a part.  If the guide pins are
corroded, would spraying them with penetrating oil loosen them enough to
remove and lubricate?  It looks like I may need new rotors as well.  Did you
have to replace yours?

 Elliott,  thanks for the heads up on the proportioning valve.  I'll look
for it, but as you say, it is probably not on my quattro.  I appreciate all
of the help.

Best Regards
David Torrey

'93 100CSQ Avant  128K miles
'88 Saab 900S  213K miles
'87 Saab 900S  207K miles
'79 BMW 320i   100K miles