i'm going thru some a-body front discs on a b-body issues. i don't have an answer to your problem but i do have some observations. when i switched from a 1.03 bore master cylinder to a 15/16 bore master cylinder the calipers would lock up. switched back to the 1.03 and the calipers are free. neither master cylinder has residual valves. the pistons in the calipers are very tight; i think too tight. i think the 15/16 bore master cylinder is applying more pressure moving the piston out of the caliper further. because the pistons are so tight they just can't release. i'm trying to find some rebuild kits (o-rings-dust shield) to see if i have the wrong o-rings. i hope yours stops better than mine, 'cause mine ain't worth two dead flies!