Replacing brakes system

[shadowgray396]

Maybe the master cylinder and not the booster. I agree with Hank about moisture in the brake fluid. I would do an inspection of of all the brakes first, make sure the rear brakes are adjusted correctly and no leaks around the rear wheel cylinders, the front disc are working correctly and you don't have a frozen front piston, new fluid in the system and see where you at.
My stock brakes work great, but everything is new or rebuilt. I'm also running synthetic brake fluid so I don't have a moisture problem.