Hi,
 can anybody tell me wether a gecko 340 servo drive will be wrecked if
is back driven by a servo generating current?
  What I mean is that I would like to retain the handles (retractable) to
use my mill manually,I am just concerned that turning the motors might
burn the drives out?
  cheers
   tony

Gecko has no warning about that in their extensive instructions.

I have turned my steppers many times and lit up the power indicators on my Gecko203V with no apparent ill effects. But that doesn't mean it's OK.

That would be useful info to ask Gecko and then post back their answer. I just got my first 320 so I'm interested also.