Iron Filings in Centre Diff

[paul.heneghan@bbc.co.uk (Paul Heneghan)]

A couple of months ago, I changed all four tyres on my 1984 80q to some 
second-hand Continental Sport Contacts.  At about the same time, I noticed a 
roaring sound (like a wheel bearing noise) that was speed dependant.  I 
wasn't sure whether this could all be due to the new tyres, so I started 
thinking about the transmission (now at 140,000 miles).

Last weekend I thought I would check/change the oil in the transmission. 
 When I took out the sump plug on the centre diff, I found it had a magnet 
in it (confirmed by Bentley) and attached to the magnet was about 1/3 cc of 
iron filings.

Is this normal?  Should I worry?

I have a leak in the rear diff - it needed 500ml to top this up.

I tried to grease the UJ in the middle of the prop shaft.  Unfortunately, 
the nipple doesn't point outwards, so it is very difficult to get to - I 
have no idea whether I got any grease into it or not.  Any suggestions about 
how I can check this - is it possible to rotate the square shaft (that the 
nipple is mounted on) that attaches to the UJ so that the nipple points 
outwards?

There is a bearing close to the UJ in the centre of the prop shaft.  It 
looks OK, but if you tug on the propshaft, you can move the bearing around 
quite a lot.  I would have thought the rubber would have been very stiff - 
any comments?

Sorry for so many questions, but it is difficult to find expertise on these 
relatively rare beasts.

I saw one in a magazine for UKP350 which needed a new wing and headlamp - I 
nearly bought it for spares, but my wife would never allow me to keep it in 
the drive.

Paul
paul.heneghan@bbc.co.uk
1984 Audi 80 quattro
1983 Audi 100 Avant