I don't have a spring pulling the pedal back. I did confirm that the is about 1/16 or so play in the rod. I also never had this problem until I swapped the master cylinder. I have since replaced it with two new ones and still the thing the master cylinder is a 1972 Chevy pick truck. It's just had to believe i have gotten 3 bad master cylinders. The only thing left is the brake lines I confirmed nothing is running by anything real hot. I even checked the fluid temp when the brakes we locked up and it wasn't even warm. The other weird thing is the pedal got real hard to push the worse it got. It only had maybe 1/2 to 1" of throw when the brakes were really locked up