I have a 2000 Regal LS with 98k mi. It is a great car and I would like to hang on to it . The car has developed one nerve racking trait over the past year. There is a vibration , sort of side to side between 35 and 45mph.After that it smoothens out until 70mph .I do know that it is not tire balancing. It seems to do it in any gear! Any ideas or experience?

Front end parts are just wearing out. An good alignment shop will help you out.

your Tires are probably balding on the inside also...

you need ball joints.. lower im guessing.

and NEW TIRES THAT ARE BALANCED

This is a late entry but could help someone else.

Actually , as it turned out, the vibration was caused by a worn wheel bearing! I probably should have posted that but I had forgotten about the posting on this forum! Thanks again!

sweet that helps.

wheel bearings usually make a humming sound.
they dont usually make your car shake...