3.09 gear set with 3.23's

skep419 said

I’ve tried. (Pinion angles, driveshafts, wheels/tires, 3rd members, 904, a833, etc)

3.23’s puts the vibration above 100mph.

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Axle bearings? Bent axles? That vibration would be the first thing I’d fix. Not much fun having a nice engine in a chassis that can’t use it. I wouldn’t spend much more time trying to “gear” around the vibration, it ain’t gonna get any better.