i have a 98 z28 lowerd and i still have the stock panhard rod. The rearend is off centered would that cause a vibration.

 

With a standard 1 to 1.5 inch lowering, usually no. Stranger things have happened though.

Did the vibration start right after you lowered it?

Ramey

 

I bought the car lowered and from st louis and i did alittle.But i really noiced it when i put the 315s on and i have a lot of road noise also.....also it has a 8.8 ford rearend. i do plan on doing a adjustable panhard rod very soon

 

Did you ever check the pinion angle? 1 degree split between drive shaft and torque arm?

 

315's will increase ride harshness, and noise. I suspect Ramey is on the right track though. Start by check that pinion angle. An unbalanced driveshaft, u-joint wear, or both will also cause vibration.