i had the vibrations in my pedal at once also. it only stopped when everything in the bell housing broke one day. it had only done it for a few days though. but anyway i learned that everything was worn out. there is a collar that the bearing rides on that sometimes gets ridges in it, also there is a lead weight on the fulcrum that can get loose. last but not least the post that the fulcrum uses when it is enaged can wear out.......hope this helps also if some of this is wrong then you may also have other problems like a bad presure plate that is out of balance causing the vibrations with the engine.