fitted loads myself and never had any problems at all so looks like you got unlucky depends how bad the vibrations are slight vibration through the pedal when it is depressed is normal on cars with hydraulic clutches as the pipes are usually mounted to the engine or gearbox and the vibrations you feel are just the engine moving about against its mountings, excessive vibration could be caused by a loose flywheel i have seen this on a focus it aint good cus this one had parted company with the crank and smashed throught the side of the block, smashed the bellhousing to pieces, smashed the rad and dented the bonnet! luckily it didnt go through the bulkhead and into the car as that has been knoen to happen before (so ive heard!)