The brakes are applied when coupling has moved about 2" .. as there is just over 5" of travel of coupling brakes are really locked on hard.
Once locked on you cannot rotate wheel backwards, just too much pressure of shoes on drums.
No amount of trying adjusting shoe gap, adjusting rod play has fixed this.,
It has been into 2 Indespension dealers - and both gave totally different advice, and failed to resolve it
I have spent must be at least 60 Hrs on this.
I'm not going to waste anymore time ..........
I have my 'locking pin' workaround - I'll live with that - frustrating but where we are on this.