  We perform a phenomenological analysis of the decays $B \to D^{**}\pi$, where
$D^{**}$ is a $P$-wave excited meson with total angular momentum $j = {1 \over
2}$ or ${3 \over 2}$ for the light cloud, recently measured by the Belle
Collaboration in the modes $\bar{B}^0\to D^{**+}\pi^-$ (Class I) and $B^- \to
D^{**0}\pi^-$ (Class III). Making the reasonable assumption of naive
factorization, that we test in $B \to D(D^*)\pi$ decays, Class I decays allow
to extract the Isgur-Wise form factors $\tau_{1/2}(w)$, $\tau_{3/2}(w)$ at $w
\cong w_{max}$ ($q^2 \cong 0$). We obtain $\tau_{1/2}(w_{max}) < 0.20$,
$\tau_{3/2}(w_{max}) = 0.31 \pm 0.12$. We discuss the question of the $w$
dependence of these IW functions. We find agreement with the Bakamjian-Thomas
quark model of form factors and, extrapolating at $w=1$, with Bjorken and
Uraltsev sum rules. We discuss also Class III decays, where the $D^{**0}$ $(j =
{1 \over 2})$ emission diagram contributes. We extract the corresponding
$f_{D_{1/2}}$ decay constant, that is in agreement with theoretical estimates
at finite mass. Finally, we must warn that $1/m_Q$ corrections could be large
and upset the results of the present stage of this analysis. On the other hand,
we confront present data on the semileptonic rate of $B$ mesons to excited
states with theoretical expectations.
