Inadvertently exceeded driveshaft "Critical Speed" at Willow Springs.

jos51700 said

A sufficiently sized aluminum shaft should be more than stable. Cars have run faster than yours (with overdrive) long before carbon fiber shafts were available. Crown Vic cop cars have aluminum shafts that ought to work well in an A body. It ultimately depends on the mass of the shaft.

Have you taken the shaft to a different balance shop? Checked trans mount, u joints, tail bushings (new doesn't mean "right"), etc?

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An aluminum 4" might take care of it, but critical speed is a calculable factor, and the math still doesn't add up for predictable rpm safety. I will run my numbers past the techs at QA1 to verify my set-up.

The 52" long center to center driveshaft was made at Strange Engineering, so it is a quality piece. Regardless, I took it to my local shop to have it checked, and he was amazed at how well balanced it was. He also inspected both u-joints and all checked out good. I replaced my transmission output bushing and it was nice to begin with.

I'm going to adjust my pinion angle to just under 1 degree down and my transmission angle to 1 degree up. That's 2 degree down pinion angle in relation to the transmission centerline with equal angles at each end of the shaft to equalize and cancel out joint phasing.

I'm also going to install a driveshaft that's critical speed is rated higher than I could potentially spin it.