misc 93 90 questions (somewhat long & rambling)

[Elliott Potter <epotter@abraxis.com>]

Until I came to this list, I had always been pretty pleased with the
brakes on my 93 90CS, comparing them to those of my 85 4000S and 95 Peej
Grand Cherokee.  Thanks to you guys, I'm now only somewhat pleased with
the brakes (and other aspects of the car).  Then I got a crazy idea--I
really like the new 5-spoke wheels on the 1.8T (and most of the other
new Audis these days), and had tossed around the idea of buying a set
and switching them out.  Then while I was at the Goodyear shop having a
nail hole patched in one of the tires, it struck me how pitifully small
the rear brakes are.  My question: is there a difference in size in the
brakes on the 1.8 and my 90?  If so, is it possible (ie without large
physical alterations) to put the 5-spoke wheels and the 1.8's brakes on
my car?  Of course if the brakes are the same then it doesn't matter.

Another question: the 4000's fan stays on after the car is turned off
(as we've been discussing recently), but the fan on my 90 doesn't...  It
didn't strike me as important until one day when I was checking a fuse I
noticed 2 missing--both had to do with the low-speed radiator fan. 
After about a week (yea ok sometimes things just don't connect) it
occured to me that I couldn't recall the fan ever running on low
speed--just high(very) speed.  Is there a low-speed setting on this
fan?  If so, does anyone know why it might have been disabled?  Is it
possible that the guy who puts fuses in the car was having marital
problems/drunk/half asleep/whatever and didn't put them in?  In
retrospect I don't think they were ever there.  If I just put in the
missing fuses, will my car spontaneously combust?

I just read someone mentioning an amplifier board on the rear speakers
of their 90 underneath that huge metal basket...just containing a
transformer and a capacitor?  If that's all it had it's most likely a
second-order low-pass filter (part of the crossover).  If there are 12v
going into it then I'm probably wrong as what I'm thinking of is a
passive filter (uses no volts).  I might check that out this weekend if
I get time, as my rear speakers are starting to act up again...

Last one: I've got an auto. transmission, and in a couple of places
there are large, bold-faced instructions to check the differential fluid
(not the stuff you check from the dipstick).  This should happen every
30K miles.  Flipping through my reciepts I noticed that for some reason
we skipped over the 30K service, and I don't know if this has been
checked.  What does checking this bit of fluid involve?  I recall the
auto trans on my 4000 died about a month before the recall notice (had
to pay for it myself; got reimbursed about a week after the recall
notice was issued...good experience) and I would like to not have that
happen here...


Thanks!

Elliott