As noted, 1979 W123 -

Car is smooth as can be at low speeds, whether turning or driving straight.

Remains smooth all the way up to highway speeds (70mph) when going straight.

However, when going around a bend at highway speeds in either direction a vibration occurs that can be felt exclusively in the steering wheel. Nothing felt through the seat, or the feet. It's fairly mild, does not affect the feel of control in the turn, and goes away as soon as the wheel is straightened back out.

The car has new tires. Rubber boots on the ball joints are intact. Tie-rod boots have cracking on the surface from age but none appear split open yet. Suspension is very quiet and feels well controlled over bumps and around corners in the city. There is a creaky old pirate ship sort of noise when steering at low speeds, such as when backing out of a parking space; nearly every W123 I've driven has done this and I've always attributed it to a bad idler arm bushing but haven't fixed any of them yet.

Any advice on where to begin? Any thought on the idler arm bushing being a potential culprit? Can a bad one cause this type of symptom?

Thanks in advance.

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1979 300D 040 Black on Black - 1985 300D Maaco job (sadly sprayed over 199 Black Pearl Metallic) on Palamino

http://i.imgur.com/LslW733.jpg

The Baja Arizona Oil Burners Send a message if you'd like to join the fun
Left to Right - UberWasser, Iridium, Stuttgart-->Seattle,, mannys9130

Visit the W123 page on iFixit for over 70 helpful DIY guides!

Sounds like a tire needs balancing.....also possible wheel bearing issue.

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[SIGPIC] Diesel loving autocrossing grandpa Architect. 08 Dodge 3/4 ton with Cummins & six speed; I have had about 35 benzes. I have a 39 Studebaker Coupe Express pickup in which I have had installed a 617 turbo and a five speed manual.[SIGPIC]

..I also have a 427 Cobra replica with an aluminum chassis.

Second vote on the wheel bearings. Remove the wheel, remove the brake pads, and spin the rotor. If you hear or feel any noise, it's bearings.

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'83 300D, 126K miles.

Thanks. I didn't think about that. I'll jack it up and check that. I will also tug on the wheels before removing them to see if I get any play.

If the bearings seem OK, I'll rotate the tires so the fronts are moved to the back and we'll see if that changes anything.

__________________
1979 300D 040 Black on Black - 1985 300D Maaco job (sadly sprayed over 199 Black Pearl Metallic) on Palamino

http://i.imgur.com/LslW733.jpg

The Baja Arizona Oil Burners Send a message if you'd like to join the fun
Left to Right - UberWasser, Iridium, Stuttgart-->Seattle,, mannys9130

Visit the W123 page on iFixit for over 70 helpful DIY guides!