That's part of the reason I zeroed in on the pinion angle as my first guess. The RPM difference between 3.42 and 3.90s at 60 isn't great so I'm not certain but I'm confident.

You're not the only one that has issues with this stuff. I know Sieg chased a driveline vibration for days - trying minute angle changes until it was gone or mostly gone.

It can be other things too --- too much yoke stick out.... Driveline balance... a tire(s). But from what you said your set up was -- you need to sort that out first. And THEN buy a seat!! LOL

Trey, Greg is correct. Get the pinion side of your rear up, ideally at the same angle as your tranny is down. If tranny is down 2.5, your rear should be up in the front close to the same, as to run parallel. It's best to find these numbers with your cars frame as close to level to your shops floor, as possible. If a vehicle has a rake to it, for instance, you'd always get a false starting point number from your smart level...of course parallel is parallel.
Leaf spring cars "like" the pinion down a bit more than a link car, because of the movement the rear sees during acceleration. Especially leaf spring drag cars. Get some shims, and it should fix your problem.

Trey, check out the video link in open discussion, titled driveshaft phasing.

I saw it and plan to watch it when I get home. Thanks, Scott.

I got the 4* shims in over the weekend. The pinion is now just under 1* up. I didn't get time to test it out due to my sister having her third baby last night. I also think I need to realign the rear before I get it up to speed to see how it reacts. I think I measured wrong when I was reassembling everything. Hopefully, in a few days I can try it out.

Thanks

When you're certain the housing is square in the chassis mark the spring and perch on both sides with a paint pen for future reference. :thumbsup:

Now I feel dumb, lol. Such a simple idea. Thanks Scott. I'll do it!