Stock '66 Chrysler 300. 383/727 carter AFB #4131S

Drove it round a bit today up and down some hills, kind of warm outside.

When I shut off the ignition, it backfired through the carb about 3 times in quick succession, ending with a nasty whizzing sound and a puff of smoke from under the hood (ka-chunk ka-chunk ka-chunkwhizzzzzzzzz). Now it runs like crap and the power brakes don't work. I have to stand on both the main and parking brake pedals to stop the car. Any ideas on what happened and how to fix it?
-Chris

Have you checked the vacuum lines.
maybe a split in the vacuum line from carb to booster.
Check the PVC and that vacuum line aslo.

vacuum lines look good. Could I possibly have blown the diaphragm in the power brake booster? Has this ever happened to anyone?

I'm wondering if the backfire(s) fried the check valve in the booster.

Check the second nipple on the booster. It should have a cap on it unless you have cruise control.

Ok. Thanks for the help guys. I looked at the check valve and it was indeed broken- backfire blew the entire top off, but it looks like the rubber valve is intact. I think I'll just RTV it back together for now. Anyone know where I can find a new valve though? Anyone know of a specific part part number or what to spec at the parts store or will I just have to jury rig it?
-Chris