Power to Manual Brakes - D150

My 79 D100 was a manual everything truck. Manual brakes, manual steer, 3 on the tree. and as long as I kept those back brakes adjusted up I never had any issues with stopping. and I towed and hauled ALOT with that truck, I am sure I was deep in 3/4 ton territory with it several times. Manual brakes don't scare me.