'91 100q Alternator Belt Screech & 400-500rpm Idle Speed

[mboucher70 hotmail.com]

Along similar lines, I started experiencing a belt screech earlier this 
summer.  I figured it was the A/C belt because it only happened when the A/C 
was running at the moment when the car went from stopped and accelerated to 
move off.

Got all ready to tighten the A/C belt, got on the garage floor where I could 
get to it, and to my surprise, the A/C belt was quite tight.  The alternator 
belt was a little slacker than it should've been, so I tightened it up and 
the noise went away.

Fast forward through a long, hot summer of hard driving and pushing this old 
beast through some record setting temperature days.  Towards the end of the 
summer it started squealing again.  But only when the A/C is on!

Ever heard of an alternator belt that squeals ONLY when the A/C compressor 
is running?

Belts look good, have about 10,000 miles on them, and were sold & installed 
by a shop that only does Audi/VW's, so I'm pretty sure they're the correct 
belts.

-----Original Message----- 
From: Fred Munro
Sent: Tuesday, September 18, 2012 8:24 AM
To: wadd-wadd at usa.net ; quattro at audifans.com
Subject: RE: '91 100q Alternator Belt Screech & 400-500rpm Idle Speed

There are a few things to check.
Are you using a metric V-belt (i.e from the Audi dealer) or a SAE belt from
your local FLAPS? Metric V-belts use a different numbering system than SAE
V-belts and some metric cross-sections cannot be matched with SAE belts.
There are cross-references available to match up belts, but before using a
SAE belt you should check for differences in length, cross-section, and
ride-out. I had a squealing problem with my first Audi ( an '86 5000tq) and
solved it by using metric belts from the dealer.
If a V-belt is worn, it can get narrow enough that it bottoms out in the
pulleys - if the top of the belt sits below the outer edge of the alternator
pulley it may be worn too much.
Check for wear on the pulleys. Pulleys don't last forever and these cars are
getting enough hours on them that the pulleys may be losing their profile to
wear.
Are all the pulleys aligned in the same plane? If one pulley is cocked at an
angle (i.e. the alternator mounts allow it to twist a bit) the belt will
squeal and wear.

HTH

Fred Munro
'97 S6

-----Original Message-----
From: quattro-bounces at audifans.com [mailto:quattro-bounces at audifans.com] On
Behalf Of wadd-wadd at usa.net
Sent: Monday, September 17, 2012 9:37 PM
To: quattro at audifans.com
Subject: '91 100q Alternator Belt Screech & 400-500rpm Idle Speed

Two issues with my '91 100q

-the alternator belt lets out an embrassing screech every other day
regardless of how much I tighten it. Any way to address this? Any special
belt or dressing?
-the idle speed is about 400-500rpm. The car doesnt stall though.

Thanks!

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