70 Challenger New Brakes, Losing Vacuum. Need Help.

So we just installed new brakes on the Challenger. When the car is in neutral , going down a hill the car stops perfectly, as soon as you put it in gear , it loses vacuum and the brakes don't respond as well at all. any ideas? thanks

Check tha vacumm on your engine at idle, and in gear with a gauge on the manifold port, chances are your pulling 12 or more inches in idle with the RPM slightly higher, but in gear your probally doing 10 or less inches,......if your cam is a high lift/duration, it's eating up your vacumm,.....unless you have a vacumm leak somewhere,....if your cam is the culprit, your gonna have to invest in a vacumm resv. can and pump

Mike