- The tires on the inside. I had a tire deform on the inside and it started rubbing on the tie rod end. Make sure there's no rub marks on the tie rod or tire.

- Wheel balance. Always seems to be the problem for me when I get vibrating.

- Tie rods. I'm guessing that this is the problem. When the vibrating occurs on the highway, do a slight but QUICK left then right turn of the steering wheel. If it helps to stop the vibration for awhile it's probably the tie rods.

Another way to check the tie rods is to jack up the front end of the car. Grab the left and right sides of the tire with your hands, and then alternately push your left hand in while pulling your right hand out, and vice versa. If there is any movement it's probably the tie rods.

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1980 300D
1977 450SEL