Quote Originally Posted by petrified.rabbit View Post
did you replace the check valve with the booster?

it sounds like the leak caused air in the system, and a bleeding would solve it. But if its just one or two times and then everything is normal, it could be a vacuum bleed down from with the check valve, or reservoir. And it works fine again once you build enough vacuum.
Does feel like its a vacuum leak. Maybe someone can tell me where is the check valve located? I assumed the check valve built-in to the break booster. If I am understanding right is the check valve is a separate part from the booster? I still have the same problem even after we bled the brakes. Thanks again for the responses guys!