Vibrations

Good afternoon folks,   I am dealing with a vibration that does vary with speed ( Not in front) My 84 s 12 is 302 swapped with borg warner 5 speed. This is not related to engine speed.  I have had the custom steel drive shaft checked for balance and run out.  Replaced the trans mount as well.  Motor mounts look fine.  I have yet to check the newer tires ( BFG sport somethings on maxima rims) though I do not think tires rims problems.  Drive shaft looks straight on though I have not measured pinion angle.  The diff is R200.  Any body have a suggestion ?  Going to be a nice weekend in Michigan.

Could be the rear bearings?  You may want to try to flip your rear tires if they are directional.  Could be a bad bearing in the transmission.

tire are directional but did check they are going the right way.  Transmission shifts fine, vibration is felt in shifter though. The problem is not in clutch or engine, vibration is speed related.  Friend let me borrow go pro camera I will mount underneath to "see" if anything obvious.

Really this could be as simple as having thrown a weight on one of the rear wheels or a warped rotor. I suppose to get the best sense it would require a ride in the car.

I also started to feel the vibrations real strong. It was moving my steering wheel a lot. I'm thinking it could be the transmission mount. It feels directly coming from bottom of the shifter.

Pinion angle

The angle of the driveshaft to the diff must be the same as the angle from the transmission to the drive shaft. Both vertically as well as horizontally.

Update to vibrations ended up being tire bf Goodrich 255 55 r 16 had high and low spots this was clearly visible while on balance machine. My thinking was something else these tires looked fine. Got two new rears not as wide 225 55 r 16 rides so smooth