86SS - High Speed Vibration

[ed1948]

My original stock 86SS has around 90K miles. At HWY speeds there is a little body vibration. The tire shop says the tires are balanced but vibration could also be from the drums or the driveshaft. The transmission tailshaft bushing has looseness and the U joints are recent.
-could the tailshaft bushing being loose cause driveshaft vibration?
-could the age of the rear axle locating rubber bushings , the rear trans mount being compressed and the slight settling of the rear suspension cause the driveline angles to be off thus contributing to vibration.
I don't want to throw parts at it. I'm just at the diagnosing stage and it's still too cold to work on it.

 

[vandyman]

My original stock 86SS has around 90K miles. At HWY speeds there is a little body vibration. The tire shop says the tires are balanced but vibration could also be from the drums or the driveshaft. The transmission tailshaft bushing has looseness and the U joints are recent.
-could the tailshaft bushing being loose cause driveshaft vibration?
-could the age of the rear axle locating rubber bushings , the rear trans mount being compressed and the slight settling of the rear suspension cause the driveline angles to be off thus contributing to vibration.
I don't want to throw parts at it. I'm just at the diagnosing stage and it's still too cold to work on it.

I would lean towards the bad tail bushing. The drive shaft is not being balanced correctly.
I had a drive shaft that was not balanced and it would vibrate between 55 and 65 mph.

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[fleming442]

I had that once; I didn't have the rear u-joint seated correctly in the yoke. I'd check that first.

 

[motorheadmike]

Jacked up driveline angles are possible. So are bent axle flanges.

 

[ed1948]

The rear wheels spin true, u joints confirmed to be seated correctly, he balance weights on the driveshaft are in place.
I'll report back once temperatures warm up.