2 things usually cause a shimmy
Loose steering and bent or out of ballance tires/wheels
rarely caused by kingpin


1955 GMC 150, 1980 Chevy C10, 2011 Sierra 3500 HD SLT Duramax Dually Crewcab, 1960 Chevy BelAir 2dr sedan, 1978 Pontiac Trans-Am