79 200 series Van 318/727.

Sitting at idle its ok. Press the brake pedal and it gets rougher, tries to smooth out but the engine shaking is noticeable since its right there in the vehicle. foot off the brake pedal and its back to normal. Do I have a 'bad' booster ? With the new carburetor I can actually get the engine to idle properly, with the old BBD it was all I could do to get it to run at all sometimes. Before the conversion to 4bbl, just running with the engine cover installed and pressing the pedal at idle I could hear a moderate 'woosh' sound and thought it odd but nothing more. The crappy idle before probably helped to mask the problem.

Booster is a cardone reman from the local store, maybe 3-4 years old at most.

Had same thing happen several years back...the seal that the rod goes through from the booster to the master cyl. went bad causing a vacuum leak.

Oh, and I just remembered, the real problem was a very small leak from the master cyl. onto the rod causing it to rust and ruin the booster seal.

My van has an extra port on the vacuum hose fitting going into the MC. The caps I put on seem not to last long, and leak. Might not be the problem, but it's an easy check.