My parts book shows all 150's use the same p/n steering rods, left and right are slightly different lengths/p/ns.
Steering rods are tubes that are hooked to the rudder pedal cross tubes and the rod is hooked to the steering collar, there is a heavy spring inside that will let the rod extend slightly or let the rod retract with no resistance. They are generally pretty bulletproof. If the rudder system has been rigged correctly, I don't believe they should have an effect on shimmy.The swivel joint at the tube end of the steering rods is adjustable and I've seen some of those too loose, they are a bear to get to in the plane to tighten up.
I had loose rudder cross bar bearings and replacement of those gave the steering rods something to pull against to resist the shimmy.
Alan

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