The drive works perfectly for double sided disks (using the
appropriate index hole).
Yea, 8" drives are a bit funny like that.
You know this, because context. Some future google-ologist might not.
So. 8" drives have a different index position for SS and DS.
In your case I suspect either the emitter LED or the receiver
phototransistor ro maybe the wiring or what ever conditioning on the
PCB is b0rken for the SS sensor.
Assuming of course your drive has two sensors -- I have not yet owned
an 8" drive like that, the ones I have had were dedicated SS or DS.
W