The two rear ports on the master cylinder are teed into one line which then goes through the biast valve and tees off again into each caliper at the rear. I also jointed out the biast valve to see if it was faulty but made no difference I also wondered if this was somthing to do with the problem,cos like i said my mate just changed the drums for calipers with the coversion bracets on his cabbie with out touching any thing else and his brakes work realy well.So he will still has the diagonal split?