Shakin' Saturn

I have a 2004 Saturn ION Sedan with 38000 miles on it. It vibrates between 40-50 MPH and only then. I have had all the tire rebalanced and rotated to no avail, any suggestions?

If you have a defective tire, all of the balancing in the world will not rid you of vibration at certain speeds.

I suspect that you have an internal separation in one of the tires, and this can be a dangerous situation. Have the tires inspected by a mechanic OTHER than the person who balanced and rotated the tires. A well-reputed tire dealer is more likely to spot the tell-tale signs of internal separation than someone else.

a Road Force Balancing machine can detect an internal defect. It spins the wheel while applying simulated road forces by pressing it against a spinning drum. It’s far better at confirming these type of problems than a regular balaning machine is.

You might also want to “read” the tires. Scalloping, feathering, and other treadwear irregularities can be excellent clues. How many miles do the tires have on them?

If rotating the tires made no difference you may be dealing with some other cause. Perhaps a good chassis shop can look at it.