Mike1

Can't say i've been in the position to do this to a Sierra.... If i recall they have a tie rod so adjustment could be achieved there. Well I think the front wheel location is achieved by the ARB that locates into the track control arm. If you were to put some sort of shim/spacer at the back interface of the TCA and the ARB it would effectively push the front wheel forward slightly in the arch ( the ARB is mounted behind the TCAs ). I guess this would be useful to equalise caster from one side to the other although I don't know the effect of differing settings on one side compared to the other.

That's quite interesting. The caster on a Sierra is normally non-adjustable ( unless you have top mount caster/camber adjustment or compression strut set-up rather than the front ARB locating the TCAs ). Have you ever managed to bring about any adjustment on one with the standard set-up when the left/right measurement differs markedly? Or is it not worth worrying over? I have heard of people using very thin shims on the ARB/TCA junction?