its not the rubber pads, its either gotta be the clutch or flywheel your using, and id more than likely say its the flywheel. The balancers for an engine is made for a particular combination of the block itself (crank, rods, pistons) and the flywheel also.. and of the rotating parts are taken into consideration to balance,,and the harmonics of an engine. this also includes the flywheel for an automatic transmission. Such as the most serious difference like wrench said is the 400 combination....another example is the 305 takes a different balancer combination... unlike most popular belief,,, ALL chevy small block parts are not interchangeable...sure they will fit.. but can be a bad combination...
it could also be the clutch disc..?? or the transmission pilot shaft..?? did your have a pilot bushing..???
