I have a frustrating vibration problem. It starts occurring at around 80 mph and gets worse the faster I go. It seems to be coming from the rear. I thought it was the driveshaft, so I had a new balanced aluminum one put in. Now it’s a little less severe and happens at a higher speed.(80 versus 75 with the old driveshaft) I also had the tires balanced just in case. It still won’t go away. What gives?

 

When you had you tires balanced, did the mechanic watch the wheel spin to see if it was the slightest bent? If not, look at the size of the weights that were used to balance the rear tires. If you have a weight more tha 1.75 oz, then I would have the rim checked to see if it's maybe bent a little.

Also, you may have an axle that is slightly bent. Jack up the rear of the car and place it on jack stands (don't keep the car on only the jack while doing this!!). With both rear tires off the ground, start it up and put it in drive. Have someone give it gas (VERY little gas) to get the tires spinning at highway speeds and see if you notice any wobbling of the wheels. If you do, take that wheel off and do the same thing and what your hubs to see if they are out of wack any.

If everything seems straight, all of your rear-end bushings for wear and play.