[ZeGermanHam]

Originally Posted by Greg Reid

Can you tell me a little about that process? How you check it, change it and verify it?
I swapped rear ends last year and have the same symptom at the same speed.
EDIT- Scratch that... I see that you used adjustable aftermarket suspension parts at the rear. Mine is a factory setup so I suppose my vibration is from another issue.

Yes, I did use adjustable upper links for my differential that allow me to change the pinion angle.

I'd still recommend verifying the pinion angle in your car even if you have stock, non-adjustable upper links. To check it, you'll want to elevate the car on level ground and have the full weight of the car on the axle or wheels. For people without a 4-post lift to drive onto, that would mean supporting the car by placing jack stands under the axle tubes so the rear suspension is weighted. From there, you will want to disconnect the driveshaft from the rear and use an angle finder (can be a free phone app) to determine how many degrees from zero you are at. My understanding is that the reading should be in the ballpark of 3-degree (not less), and equal and opposite to the angle of the output flange of the transmission.

So if the transmission is angled downward 3 degrees, the differential should be angled upward 3 degrees, give or take.

I'm not an expert on this, so someone please correct me if I'm wrong.

If you find that your pinion angle is not where it needs to be, you might need to buy adjustable upper links to get there.