when u let off the hadnbrake the spring inside the hub should pull the brakes into their 'rest' position, u could try to jack up the back off the car and pull the handbrake ,then turn both wheels,they shouldnt be able to move. the let off the handbrake and turn the wheels again,they should turn freely obviously.
when you drive it hard on a straight road and apply the brakes,does it pull to the same side everytime?
did u remove the ABS system? is the system still diagonally linked?
because of the diagonal linked lines, make sure the front calipers/pads are ok as this might make the rear having more braking force.
also make sure the system has been bleeded properly.