Greetings. I had the same problem on my 51 one ton with front disc( 2011 one ton Express van ) and stock rear drums. I utilized a dual master cyl with 7 “ booster. Couldn’t get a good pedal after a few bleeds. Went from a 1 inch bore to a 1 1/8 bore m/c and used a portioning valve rod block when bench bleeding. The insert goes into the portioning valve where the switch is removed. Center the rod, insert the “block” to prevent the rod from moving when bleeding the vehicle. WOW, what a difference, when bled, remove the block and reinsert the switch in the portioning valve.
