Shugart 800-8 media centering problem

[tony duell]

>There is no play in the spindle at all.  Certainly not 1/2 track worth.
> Can't wiggle it at all, no visible wobble, etc.

Not necessarily play. Anyway, half a track width is just over 10 thou
and I am not sure I could notice that amount of runout by eye. Also
I have learnt by bitter experience to check everything, otherwise you
discover (far too late) that the thing that was 'obviously right and
didn't need checking' was the problem


> The centering cone/clamp has just one continuous spring, all the way around.

Are you sure. The cone is in 2 parts. Normally there is a spring between them 
inside the cone and a (stronger) spring between the cone and the clamp arm.

> And, there is no point:  I did mention: I swapped those plastic
> centering cones / clamps with the other drive, and it made no difference
> to either drive.

What exactly did you swap? The cone and internal spring? The obvious spring
on top of it and all the washers? The clamp arm itself (check for burrs round
the hole where the cone spindle goes)? 

If the cone is alright then it pretty much has to be the spindle itself. Are you 
sure the spindle bearings are correctly fitted with all the parts shown in the 
service manual?

-tony