[ChrisBennet]

In my experience, SC's and Carreras cars (you don't mention the year of the car) can exhibit a similar behavior where the pedal goes down real easy and then gets suddenly firm. This is causes by pushing the pistons way back before inserting the pads.

To keep this from happening, you need to extend the pistons such that there is barely room to get the pad into the caliper i.e. you need to gently tap it into the caliper.

I take the pads out one at a time and put something thinner than a brake pad in it's place (like a screwdriver), press on the brake pedal to extend the piston then pry the piston back a little at a time until I just get tap the pad in.

-Chris