In my 79 with T5 and 31-spline 8.8, I have a driveline vibration I can't figure out. It starts getting noticeable around 55 mph and gets progressively worse as speed increases. If you've ever experienced a driveshaft out-of-balance, that's what it feels like. It's a much higher frequency than a wheel balance issue would feel like.
Rear end was rebuilt by myself and gear was changed to 3.73. I had a few driveshafts lying around so I tried a couple of them, with no change in vibration. I took 2 of these shafts to the only driveline shop within several hours. It's an hour away and I have to take time off work to make the trip... on 2 separate days (one to drop off and another day to pick up). Not convenient at all, since the shop is actually about a 1.5 hr drive from where I work.
I suspect the driveline shop didn't do a good job balancing the shafts. U-joints, T5 tailhousing, slip yoke, etc all new and tight. No slop anywhere. I opened the 8.8 and fluid looks good. Bearings all good. Pinion doesn't show signs of play, but there looks to be a little play in the spider gears. My experience tells me this is definitely a driveshaft balance issue, just being more obvious after going from 2.73 to 3.73. Am I overlooking something or should I follow my gut instinct?
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