Ok.
When my car accellerates, I get a vibration (feels like it's coming from the back) at around 30-45 mph. When I let off the gas I don't feel the vibration,
step back on the accelerator and in the above speeds, feel it again.
Lower speeds not so much and above 50 don't really feel it at all.
Within the last 2 weeks I replaced my differential pinion seal, the driver's side valve stem seals.
In december I put new tires and balance.
I am thinking that when I put the pinion nut on I either didn't torque it enough, or I might have torqued it too much. I marked the position of it before I replaced the seal.
Could it be the uv joint?
Did I maybe not put the driveshaft in far enough? Did I put it back in too much?
I need a starting point to diagnose this.

Help!!!!!!!

 

Got no replies so just went ahead and did a few things.
Found that my front u joint was pretty much shot.
Replace both u joints and tightened the pinion nut a quarter of a turn.
Vibration gone.
More than likely it was the front u joint mainly but the other fixes didn't
hurt.