are you bleeding with a helper or by yourself, I'm thinking you have an issue with the system, not the booster, I run a 9" booster with low vacuum and do not have the hard pedal issue or spongy pedal. Either you have a bad proportion valve or it traveled to far to the rear or forward or you have a wheel cylinder that isn't releasing. you should always bleed all 4 Check the rod off the pedal could be set to tight. did you bleed the MC before installing it? When I converted to disc from drum, I would go into skids when I applied too much foot pedal, I then looked into adding stock components and it was eliminated. Maybe you have too much pressure for the system and need the front brake proportion valve too, Dist. block and the hold off for the rear brakes, Are you using original Wheel Cylinders?
