Finally, the Harmonic Balancer (HB) on my 2007 100k+ mile Corvette is starting to wobble. I've read a few of our treads about it and have come to some conclusions. Helpful comments are welcome.

There is a center and outer section to the balancer, joined together with a rubbery material. It's the only thing holding the center and outer sections together. When the rubbery material deteriorates, the outer section with the 2 belt pulleys gets loose.
When it gets loose, it will start to wobble. There are many reports of squealing, which is probably the outer ring spinning on the inner section, since this outer ring, with the pulleys, carries the heavy load of the accessories connected to the 2 belts. If this spinning goes too far, the outer ring can fall off the inner section (at whatever RPM) and cause serious damage.

Now, another assumption on my part.
The service manual indicates that the HB is balanced to the crankshaft. I think this is baloney. First, there is no key-way to align these parts. If GM was to balance the HB and Crankshaft together, they would have no way to align these parts again after assembling the engine. They would need a scribe mark on each part and there hasn't been any mention of seeing that. It would save more time and money to put a key-way in! I believe that the HB itself is balanced alone, like the aftermarket ones, but that the size and weight of it is designed for each type of crankshaft to dampen the harmonics (duh). The HBs were smaller and lighter on the old 327's. I built a small block 400 cu. in. and put the 327 HB and flywheel on. Wow, did it vibrate! Found out that the 400 SB needed special "unbalanced" HBs and flywheels to fully balance the "unbalanced" crankshaft. Perfectly smooth after that.

To sum this up, The Dorman HB, I bought, looks very high quality and has obvious balancing drill holes. It's a big job, but plan to install the Dorman HB, with a new seal and bolt, torqued to specs, and enjoy a no wobble HB for another 100K+ miles.

 

You may want to consider the Powerbond, Summit, or ATI units as well.

 

LS engines are internally balanced, but apparently GM addressed vibration problems in a some Corvettes with manual transmissions by inserting weights in the front pulley. That's what the service manual is referring to. If you've got weights in yours, you're supposed to mark the pulley orientation relative to the crank and transfer the weights.

I've never heard of anybody actually encountering a factory pulley with weights installed. ATI says the number of affected cars was "very small."

 

GM considered everything balanced so techs don't make a small problem worse....even wheels and rotors are instructed to go back on in the exact position they are removed during service.

I've had an ATI pin kit since I lost a balance at Mid Ohio in 2002. Whether OEM style or ATI, I'd never install a new balancer without a pin, key or screw