55rsturbo

hi i know its not a cosworth, but i have cosworth 4x4 brakes on my s2 have put a refurb rear caliper on, and for the life of me can not get peddle after bleeding countless times, new master cylinder, no leaks any where,have pressure bled it, pumped it no joy, tipped the calipers back so bleed nipple is at its highest no luck. i wonderd if anyone had encounterd any similer problems. cheers frankie