had a nosewheel shimmy on my 65 180.it usually occurred on landing rollout slowing thru 40 kts. The horn bolts to the top of the nose strut; attatched to the horn are the 2 rudder cables, and the shimmy damper. my damper was ok, but the quarter inch bolt holding the horn to the top of the strut was loose despite being safety wired. I noticed the bolt hole in horn was larger than necessary, probably since new. I got a bronze bushing at a hardware store, reduced its outside diameter, cut it to length, put it in horn hole. Now bolt is a snug fit in horn hole, no more slop or shimmy!