[BarryGMC]

OK. It really does not matter how you hook it up. A dual pot master cylinder is just two separate hydraulic circuits. Internally connected. It's the same on a disk- drum setup. Only difference is that the calipers have larger pistons and cylinders and require a bigger resivore of fluid to compensate for the larger volume as the pads wear. So now let's visualize what's going on with the booster and dual pot master. With the engine running and no braking,engine vacuum is applied equally to both sides of the booster diaphragm. When you apply the brakes the firewall side of the booster is opened to the atmosphere. The rods from the pedal to the mc are continuos so vacuum + atmosphere forces the diaphragm towards the mc. This decreases pedal effort but does not increase output pressure of the mc. This may seem wrong but it's not. The input energy to the mc is the same. Boosted or not. Un boosted it may take 50 lbs of pedal energy to stop the truck. Boosted May be 25 lbs of pedal energy. The other 25 is from the energy transferred from the diaphragm to the rod. This energy is just atmospheric pressure acting against a vacuum. So if all of the hydraulic circuits are free of air the input energy should transfer to the wheel cylinders equally. This leaves only two options for your brakes to not operate properly. First you still have air in the front hydraulic circuit. Or the residual check valve is missing on the front curcuit. My bet is the later. I have seen this a lot on dual drum mc's. Barry