K-H brake swap done, but doesnt stop!

Usually they let fluid by them to the brakes but it doesn’t have enough brake spring pressure to force it back into the system. But if it’s bad enough, it won’t let enough fluid though to operate the rear brakes. It’s really strange to me that you couldn’t get fluid to the rears when attempting to bleed them. I figured if the drum brakes were working and then you change the balance switch out for a proportioning valve and now you’re not getting fluid to the rears, it’s probably the source of the trouble.