http://www.amazon.co.uk/GA45-Magnetic-Ca...ey+caster+gauge from Sealey at around £30 ideal for checking caster and camber.
Indeed there will be barely a touch of shimmy with 6 degrees caster (Gemmer or R&P) and rest of steering in serviceable condition. But with 4 degrees caster and no damper very good chance it will kick in at around 55 mph.
Regards PJB.