1987 300sdl - car was driving perfectly.

Left front tire replaced - blow-out while doing 5-10 mph- replaced with spare immediately. Care drove perfectly with spare.

Both front tires replaced using same rims at local tire shop. Front end vibration at 55-60 mph. The 'jiggle' is barely noticable at lower speeds. It can be felt in the steering wheel.

Rear tires replaced as well. Problem persists.

All tires rebalanced on a Hunter balancer. Twice. Tires were only very slightly out of balance first, perfect second time. Problem persists.

Back to local tire shop- removed front tires and replaced with used tires for comparison- problem persists.

Had front end checked- ball joints replaced and aligned.

Borrowed two rim/tire combinations from a friend and put on front- problem persists.

Problem seems to be worse when it is colder outside. It feels exactly like a knot on one of the tires, but no matter what I do the problem doesn't go away. As long as I don't drive in the 55-60 mph zone it is hardly noticable.

I don't know what to do. The car used to drive so great and now it has the &)(*^&_ vibration. I have tried to correct it to no avail. Is it possible that the rotor(s) are warped? Any other issues? Any tests to diagnose where the jiggle is coming from? Could a bad strut cause this?

I am going to try another set of wheels/rims from another friend. I thought that the tire shop may have overtightened the rims and warped them, but so far haven't been able to pin down the problem.

Also, the 'jiggle' seems more pronounced at certain points as the steering wheel is turned. For example, half turn to the right seems worse than in straight line or to the left.

Any suggestions appreciated.