1979 D-100 pickup,bone stock 225 and 3-on the tree. Replaced clutch and all bearings and bushings as well as U-joints and tires. Still had s bad vibration. Thought I might need a new trans or driveshaft. But, try the free fixes first.So I flipped/rotated the driveshaft 180 degrees and re-installed it.VIBRATION IS NOW GONE! (I marked the shaft when I took it off and put it back on the same way, which is the correct way). Go figure? Could have been a number of things. But, I finally figured it out. Hope this helps you guys!

If I had to guess, I would say the way the vibration is gone??

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An officialis Tyrde-Browne Racing membrum

I just replaced a bad rear u-joint on the truck to fix a vibration. It didn't work which made me immediately think that whomever worked on it before had it 180 off. A friend told me that used hose clamps on some recalled (nonMopar brand). The screw had enough weight to it that you could dial it around the shaft to soften the vibration. I've got some real strong harddrive magnets I might try for fun.
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honey oil