On my 66 Dart, I was having an instability problem at the top end, the car was good when first put together but became worse over the years. Car was squirrly at over 100 mph, the faster it went the squirrlier it became (trapped at 125 to 126 mph), but when I let off it would straighten out. The front suspension was basically stock except for poly bushings in upper and lower arms, new ball joints, tie rods, and adjustable strut rods. It had 1.5 to 2 degrees of caster, 0 camber, and an 1/8" toe( best I could do with stock parts). Three years ago I put QA1 upper a arms, new lower ball joints and larger C-body tie rod ends and the shorter A-body sleeves, and idler arm, and set the alignment like LO23M8B said. This made the steering much more responsive which cured around 90% of the problem. After that I could feel that what was left of the instability was the back of the car swaying around. I went from a 9x26 Hoosier slicks to M/T 9x28st slicks, stiff sidewall manual trans slicks (my Dart is a stick car). A few adjustments to the Cal-Trac bars and the Dart is going straight and stable again.
