For sure hub needs to be taken apart. Regarding the back pedaling distance for brake engagement, internals will likely be version 17 discs or 23 discs. For both, brand new the disc pack thickness is about 0.75" provides 1/8 turn back pedal to brake, but worn disc packs around 0.68" or so and function fine. I even have one that is missing a disc with total thickness 0.7" and works fine but needs 1/4 turn for braking. If you 1/2 turn (180 degrees), I think too many missing discs.After doing some basic research - it seems to be what's commonly called "ghost pedaling". Also, I can move the pedals / and in effect the rear cog more than a 1/2 a turn.