Bad power brake booster?

My '69 Polara has factory power drum brakes. They work fine in normal driving but if I step on the pedal for a "panic" stop the pedal just gets rock hard and it doesn't slow down any quicker. Has anyone experienced this before? I have driven other cars with this problem and asking around some brake shops they say the usual crap like "duh what about new pads and rotors?" I know what worn brakes feel like, they are still linear and it shouldn't affect the pedal feel like that where you can't panic stop worth a damn.
Author: 360dusted