That’s true, but, there’s no combination that would effect all 4 wheels. A disk residual valve holds less pressure than a drum residual valve. So you could get the disks to drag with a drum residual valve, but neither residual valve should cause the drums to drag.
All 4 wheels effected the same with a disk/drum combo has to be either the master cylinder or combination valve. Or multiple different parts causing the same effect, which is unlikely.
