I have a Vibration from about 3k - redline, while in Nuetral. Doesn't matter if I'm reving or holding a steady rpm. The motors internals are completely stock and the car has about 38k miles. I recently put a Mcleod Twin Disk Clutch in and had it matched balance to the factory flywheel. It was off by only 14 grams, so no big deal. I have new poly mounts for the engine and trans. I had a water pump leak, which I replaced but I know the opti got soaked with coolant for a little while. It doesn't feel like a miss.

Could it be the opti? I need some options because its pretty bad!
What steps can I take to narrow down the problem?

 

did the vibration start when you added the poly mounts? more than likely that is your cause.

 

I had the same exact is on my 96 M6. Had to change the flywheel twice to finally cure the issue. Just a thought. The lt1 is externally balanced and any deviation can cause vibrations.

 

The rotating assembly and the balancer are internally balanced. The flywheel is externally balanced. It's pretty much what you said but I wanted to clarify.

I have a 3K - 6K vibration too and just changed the to poly mounts. But, I've got a lifter not pumping which is causing a severe vibration.

 

Actually..unless you have changed the rotating assembly...it is not internally balanced but externally balanced by the flywheel on a lt1.

 

I had a Centerforce Flywheel bolted up to the stock rotating assembly. The aftermarket flywheel was neutral balanced. If the rotating assembly was externally balanced to the flywheel, then wouldn't I have noticed a vibration?

 

Yes..if you had a neutral balance flywheel on a lt1 you most certainly should have noticed vibrations if indeed the aftermarket one was neutral balanced. Are you sure that it was not made for a stock lt1 and balanced or it?

 

I had the vibration before the poly mounts and thought the stock were shot, so I switched. I had flywheel matched balance to the stock flywheel, which is the recommended procedure. I'm gong to look at the harmonic balancer today and do a compression test. I may pull the valve cover to look for a broken valve spring or a bad lifter. I would hope the flywheel isn't still the cause but you never know!

 

Good luck on that. I finally just broke down and bought a new flywheel from gm and it solved my problems. I think I could change those things in my sleep now..lol.