clutch pedal vibration

Mine did the same thing for the longest time...recently it stopped doing it though...It helped a little when I put in my UPR quadrant and firewall adjuster...

Do a search about this on here and look for posts by TxSnakeCharmer...He's got a fix to it also using a piece of metal stock and a spring that pulls the clutch fork away from the throw out bearing(or something like that)

I have the same problem on my 99 cobra, and this was with totally stock setup and still have it now, which I currently have an aluminum adjustable clutch quadrant and dual friction clutch by centerforce. The shakes comes and goes, I notice it is from hard fast shifts with me and then takes time and will go away and then come back again down the road. Very annoying because it makes the clutch feel like ****! oh well, I have never liked a clutch in my mustang, I WANT SMOOTH OPERATION ahhahahaha