I have a 96 z28 with a t56 conversion. When I did the conversion I bought a Spec Billet steel flywheel. I did not have it ballanced with the original auto flexplate because I was told I would not have to. I have a severe vibration above 3000 rpm and I think it is due to this. Is any flexplate off an lt1 the same. I would like to know so I can get another one so I can have the flywheel ballanced. Please help and thanks for your time.
Steve

 

Anyone, please!!!!!!!!!!!!!!!!!!

 

I have the same problem right around 3000 rpm up to 4500 And I did the same thing I have a spec flywheel, the vibration is'nt horrible but enought to keep me from pushing the motor to hard. I am going to try putting a fluid damper on the front to see if that takes care of it. any one else have a simmilar problem? how did you correct it?

 

TTT Please help!!!

 

I wouldn't think it is due to your flexplate swap. The reason I say this is because these engines are internally balanced, meaning the flywheel and balancer don't have a role in balancing the crank. Unlike some of the older engines like 454's and 400's that were externally balanced that did rely on the flywheel and balancer. I would check the flywheel to make sure it isn't warped, some companies will ship them that way once in a while. Also, did you use an alignment tool when you installed you clutch? And does it vibrate when you rev it while the car is parked or is this only while you are driving?

 

Was the flywheel made for one piece rear seal cranks? The stock one has a small weight on it. Did the one you use have a small weight?

 

The flywheel has a small weight on it and was made by spec for a 1 pc rear seal. I was told to have it ballanced with the flexplate after I changed over everything and got rid of the stockl trans stuff. Thanks

 

not entirely true.

The LT1 is a strange animal. It is internally balanced at the front of the crank, and externally balanced at the rear via the flywheel / flexplate.

I would definitely get the flywheel balance checked before going any further.

 

I agree totally. yes, the LT1's are both int. and ext. balanced. front int. and rear ext. with the flywheel/flexplate. when I had my eng. fully int. ballanced, I had to grind off the weight from the flexplate. if i were you, Id take the stock flexplate and have them match the new flywheel.
on another note, my car is now an auto (was t56) and it also has the same vibration if I cruise at around 3Krpm. my Iroc has it with the oldschool sbc350, and my buddy john's corvette also has it. I think its just a normal vibe/frequency that is transmitted more after doin some mods that would stiffen up the chassis or eng. to chassis. but I wouldnt describe the vibe as bad as you did. so its a good chance your flywheel needs to be balanced. sucks to have to pull the trans again just to try it, but thats what your gonna have to do. also, since you also just added the trans (as in you never drove that trans before) its totally poss. the input or output shaft could be bent too. so, is the vibe speed related, or is it rpm related? can you get it to do it sitting in the driveway? or does it have to be driving down the road?
chris

 

I know mine is engine related it will do it with the clutch in or out sitting in the driveway, Has anyone tried a fluid damper on this type of vibration? I would rather throw a new damper on before pulling the tranny back out. and I would have to locate a stock flexplate to balance my clutch assembly to.

 

I'm not sure what you're trying to say here. The flywheel and pressure plate are spinning right along with the engine, clutch in or out. So if you're flywheel is out of balance it's going to vibrate either way. The most accurate balance is obtained by balancing your flywheel and pressure plate together as a unit, even though most people don't bother balancing the pressure plate as it should be neutrally balanced. As said before in this thread the balance on a LT1 setup is accomplished by balancing the rotating assembly with a "standard" counter-weighted LT1 flywheel. The flywheel isn't modified, material is removed or added from the crank counterweights so that it "matches" up to the "standard" LT1 flywheel. That's why, theoretically at least, that you can go and buy any LT1 flywheel and not have to re-balance the rotating assembly.

Also the balancer or more accurately dampner, which is neutral, isn't meant to deal with "out of balance" issues, it's purpose is to deal with the harmonic torsional vibrations that result "naturally" from the centrifugal force that any rotating mass generates.

 

mine does it when sitting, here is the prob, I need to know if all lt1 flexplates are the same so I can get another one to have it ballanced to since I did not have the chance since the guy who took the auto had it installed in about a week before I could ask to use it.
Thanks for your help.

 

You should be OK match balancing to a standard LT1 Flexplate or Flywheel. I know lots of guys who have replaced an LT flywheel or flexplate out of the box without issues.

 

thanks!!

 

Did the pressure plate have an index mark? Some do.
If not get the whole assembly balanced,Flywheel & pressure plate.