Lewis,
I've never found a set of Shimano v-brakes with balanced arm-spring tension correct out-of-the-box to date.
What I do is back the adjuster screws out evenly, then unhook the linear spring ends from their perches and gently bend them outward and then re-seat as needed to balance the base tension. Once the pads are equidistant from the rim, I tighten the tension screws as needed to provide proper return spring tension.
I once mentioned my method to a Shimano rep at MTB race and he said this was how he did it as well.
By the way, it is *much* easier to adjust pad toe-in if you also unhook the springs first.
I hope this helps.
Best,
Dan.
