Shugart 800-8 media centering problem

[tony duell]

> The clamping is not out of alignment.  If it were, the results would be
> more consistent.  Besides, the clamping is not really responsible for
> the alignment.  It is a matter of the media relationship to the spindle
> as the clamping comes down on it.

The fact that it sometimes centres properly suggests to me that it is not
excessive runout on the spindle, but none the less the first thing I would
do is remove the clamp arm and check the inside surface of the spindle
with a dial guage while turning it by hand. Then probably take out the
spindle and its bearings and check all the parts are there (compare with
the service manual or the good drive). If something there is coming out
of place it will cause big problems.

Take the centring cone apart (there are lots of bits and at least 2 
springs) and again check for anything missing. Make sure the spring
are in the right places, if you swap them over the cone will not expand
properly and will thus not centre the disk properly.

Now look for wear on the 2 main plastic bits of the centring cone. If
the inner part sticks, again it will not centre correctly. If there's wear
on the outside of the larger part, the disk may not run true.

-tony