soft pedal means that the hydraulic system has a air leak or pressure leak main spot master cylinder and so you know that it wont be soft with the car off because it uses the brake booster and the brake booster is powered by engine vacuum and one more thing im not trying to step on anyones toes but the major no no is reviving dead threads they are defined as more than three months old anyways you also have the rear wheel cylinders which are located in the brake drum also did you open a brake line like take a brake hose off or run really low on fluid because you mentioned that you changed your master did you remember to bleed the whole brake system including the master