On beam front axle vehicles, lack of castor usually causes a shimmy at moderate speeds.Are the castor shims in place between the front axle and spring? If so, is the axle tilted backwards,the thick part of the shim to the rear?I have found some need more castor, especially if the rear end is higher than the front.The factory says about 1-2 degrees,a 4 degree shim often makes a improvement in steering. Too much castor can cause it's own problems,like hard steering and maybe a shimmy like too litle castor
