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Join Date: Dec 2016
Location: NE Jefferson County, WA
Re: Vibration Diagnosing Help
The cause of a vibration can be just about anything that rotates. Your particular vibration seems to be noticeable at a certain RPM range, rather than at a certain speed, so that would indicate that you could all but eliminate tires/wheels, rear axle, driveshaft and probably transmission as the cause. This leaves anything between the balancer and the clutch assembly. From the way you describe this vibration I would lean towards flywheel and/or clutch. As for factory balancing of clutches and flywheels, I wouldn't bet the farm that one or both are not your problem. If you've ever sent an engine and related components off for balancing, did your pressure plate and/or flywheel come back with holes drilled in them? Chances are they did. Mine always do. So you may want to send your flywheel and pressure plate out for balancing.
As for harmonic balancers, they are gender neutral, automatic and manual use the same balancer.
You may want to try that spacer, although I'm betting 1/4" won't make a difference.
Also, I've never owned an externally balanced big block, so I don't know the eccentricities of those engines.
Just my .02. Good luck and keeps us posted.