It's not wrong. These are all the same balance spec for sure. The two-piece cars all have neutral-balance flywheels. Something else is going on with AA's car. Just not sure what. I suppose it's possible that the old balancer is off, or that the loose bolt is the cause...but that seems unlikely. I think the only way to really solve it will be:

1. Make sure the ignition system in good working condition. I doubt this is the issue, too, but be sure.
2. Pull off the flywheel and clutch and have a shop verify the balance of both. The flywheel should be to whatever the counterweight spec is, and the pressure plate should be neutral. If either of these is off, then congrats: you've found the problem! If not, then sadly move on to...
3. Pull the rotating assembly and have a machine shop balance it to the correct factory spec.

There really can't be much else causing this.

 

We'll see.

There may have been multiple issues at play. I'm addressing them all and hoping for the best haha.

I discussed this with RAM and based on the way they balance their stuff, its unlikely it's their product either. "That is balanced to the factory external balance specification. The balance is roughed in by program in the mill then fine tuned on the spin balancer so it is highly unlikely to be incorrect." -Mike Norcia

At this point, it's somewhat of a guessing game.

Unfortunately, I haven't been able to find a shop that can do a proper vibration analysis on the vehicle. If it persists after all this work, I'm not sure what to do. I can't afford option 3 from Matt's list so it'll just be a paperweight for a while =/

 

If its balanced that way then how is it the OP and myself have the exact same issue but mine was fixed by a heavy rebalance of the crankshaft to accommodate the "proper" balanced flywheel? Something isn't adding up here.

 

Zf doc and Mike, from Ram, saying two different things. Gotta love it, huh? I feel you man. I really do. I went through the same. Put the exact same clutch and flywheel in my 96 lt4.
My dad and I did the conversion. But, I wasn't happy with my shifts. They were too rough. So, I shipped him my whole car. It has whole kit: "blueprinted", new u joints(spicer), shim kit, short throw, beam plates and he replaced reverse gear.

He mentioned I had a vibration as well. But, it didn't shake the car like an unbalanced tire or something. I never felt it as smooth as my daily driver at the time, 2002 jaguar xjr, through the rev band. But, I also don't remember my 93 c4 auto trans being any smoother than my lt4 to redline. He went on to suggest my oem plug wires were arcing. I knew they weren't, I checked all this stuff just because that's how I am. But he was adamant to change. So I said, sure go for it.

No change with new wires.

So, I got him to talk to Mike, from RAM. Cause Bill suggested the flywheel needed balancing. I said, "if Mike gives you the green light to do so, then fine." Bill says he did. So, I called Mike. Awesome to deal with, BTW. He said, "yes, I spoke to Bill."

After the rebalance, it's smoother. But barely.

My car did have a rebuilt trans, under warranty. But, the flywheel and clutch were oem. To be honest, my ram conversion feels a lot like stock. Maybe a little bit heavier clutch pedal and slightly faster revving. I ******* love the zf6 c4's. But support for the trans itself worries me, long term.

So, when you feel the vibration, does it shake the car?

 

I can't say for sure, but I do know that GM sold literally millions of Gen1 and Gen2 SBCs with one-piece seals and they were all balanced to the same spec. They obviously didn't vibrate from the factory. This includes my own LT4 car. It was dead stock when I drove my best friend over to buy it, it was balanced at the same factory non-neutral spec as all the others, and it didn't vibrate at all.

The most obvious way this could change would be if someone replaced any parts of the rotating mass with parts that weigh a different amount and didn't get the new combo properly balanced. If the harmonic balancer is off or getting slop in its rubber isolator that might cause vibrations. And obviously if the new flywheel or pressure plate aren't correctly balanced it would cause this. If you feel the vibration even with the clutch disengaged, then there's nothing else that could be involved. The problem has to be somewhere in that list of parts I just mentioned.

 

Yes, I agree with that. It has to be either flywheel, balancer, or crank or some combination of those three. The vibration is there with the clutch engaged, albeit a little less pronounced.

Some actually did have vibration issues. There was some tech data released with four trials on it that describes how some of these had vibration issues from the factory, which I find absurd that it was allowed.

So the trials involved adding weights into different spots on the flywheel that are supposed to improve the issue.

Have you seen that data?

 

Theoretically it could also be pistons or rods, if someone replaced those with significantly lighter or heavier parts and didn't balance the rotating assembly. That seems unlikely, but at this point I would rule out anything.

Never heard of that, but I don't doubt it.