I get what is like driving over the rumble strips on the side of a high way with my Buick LaSabre. It only happens at speeds above 65 mph and if I speed up or slow down it stops. I took it to a shop and was told the left side inter or lower ball joint was loose and needs to be replace. I was not real comfortable that was the problem so I took it to another shop and was told the front end is tight and he felt the problem was the transmission shifting in and out of overdrive. He said that will cause vibration much like going over the rumble strips.
I took it to a local transmission shop and they did a computer scan. The car shows no codes. They said the transmission fluid needed to be flushed and that should take care of the problem. Cost is $120 and when I asked if that included filter and gasket I was told yes. On the way home I checked with another shop about the price of a flush and was told the same amount but they said its just a flush no filter or gasket they just flush the old oil out with new.
I feel if the oil needs to be changed then I should have a new filter also. This car has 106,000 miles and I don't know if the transmission has ever been serviced.
However I still am not convinced the transmission is the problem. I had the tires checked and was told they were fine. I will rotate the tires and see if that helps.
I guess my question(s) are, Has anyone had experience with a transmission causing this problem? And is a flush without changing the filter a dumb thing to do?