I coulldnt find this situation anywhere else so I'm looking for answers and asking for help. I have a 2012 6.7 with no brake assist. Several months ago my vacuum pump went out and so I replaced it and have had no problems since until the other day. I was stopped at a red light when i heard a funny noise and the brake pedal came up and got hard as a rock. From that moment on I had no power assist brakes. I checked all vacuum lines and hoses so I decided to check the brake booster. Well long story short oil from the vacuum pump has worked its way into the booster and over time the rubber boot inside had a tear in it. I removed and replaced the booster sure that it would fix my hard pedal but surprisingly it didnt. I eventually replaced every line, hose and even the check valve but still have a hard pedal. I checked the vacuum and even with 25 all the way to the booster it still has no power assist brakes. Anyone have any ideas???