Well here we go again. I have replaced everything when I upgraded my brakes. IE C5 brakes up front, WillWoods in the back. A 1" WilWood master cylinder and an adj prop valve. On the most part they work great. But every once in a while the paddle is hard and it barely slows down. but give it a sec and it is fine. So now I have a new booster with check valve to go in. I am one bolt away from removing my old booster.
Was wondering if it could have been just the check valve. The car makes 17" of vac at an idle so I hope that's enough. I do have some sort of filter in the vacuume hose to the booster.
Thanks

 

I replaced the booster and it is all fixed. Thanks for the help. Now everything except the hard lines are new. Stops on a dime and give you back change.

 

Spoke to soon. It still does it. I push and the peddle goes further then normal and then ferms up but no brakes to speek of. Then take foot off and fether the peddle a couple times and the brakes are back.
The only thing I didn't replace is the in line filter. I was wondering if maybe the connecting rod is to short. I never had this problem till I took off the Master Cylinder and replaced it with a Wilwood.

Well what do you think. You can see where I am going.