I have a bad engine vibtration with my NEW 383 setup and it is killing me trying to find out where it is coming from. i have pulled my T56 about 6 times in 2 months and I am tied of it already. here is what I have: 383 balanced rotation assembly from Eagle. it is for a 87 and later 1pc RMS. it is internally balanced. I have a 8" internally balanced harmonic balancer. I have 1 stock LT1 t56 flyhweel AND a SLP billet flywheel, new SPEC clutch. I listed both flyhweels because the stock one ha s aweight on it and the SLP one has nothing. I am confused on this whole internal and external balance crap. AM I correct when I say that I need to use a zer balanced flywheel with my internally blanced kit I have? can someone break this down for me. I spent $2000 on a balanced kit from Eagle and really dont want to start over again

 

when i got my centerforce flywheel they said it was zero balanced...so i would think yea...have it brought down to a machine shop and have it balanced

 

Update:

I replaced the stock LT1 T56 flywheel with the SLP one and ther is no vibration now so that means that I cannot use any flywheel that has weights on it at all.This is weird because what happens to all those guys that have bought the SLP flywheel and just installed it the way it was? How can you just go from a flywheel with weights onb it to one without anything?Anyway all I do know is that I HAVE to use a neautral balanced flywheel with my internally balanced kit. I did notice that I picked up a slight car vibration about 2500 RPMS but it went away after 3000. It did it after I put the new clutch in. I thought maybe the clutch was bad so I put in an old SLP one and it did the same thing. I will be putting the trans back in tomorrow and update again on my results.