  Hadronic tau decays belong to the processes that show a resonance-like
structure in the axial vector current in the $1-2$ GeV range. This structure,
often denoted as the $a_1$ meson, seems to show different properties in
different processes. The process $\tau\rightarrow 3\pi\nu_{\tau}$ allows for a
clean separation of weak and strong effects and a clear production mechanism.
We examine how this structure can be related to interactions between the three
pions that emerge in the final state. In particular we start from the
interactions between all two body combinations.
