Brake Problems

[Tony71c10]

First time posting here, by the way this is a great page. Long story short, I purchased a 71 c10 that was originally standard. Previous owner had rigged a booster to firewall with out brackets. So I purchased brackets and installed them. Now my brakes are hard as a rock and pedal has about 3 inches of travel. I tried to bleed rear brakes but got no fluid to rear. Im thinking the proportioning valve might be the issue. Im going to purchase a new booster and brake cylinder, but cant find a proportioning valve at the located parts store. I have front disc oand drums in rear. Thanks in advance