  We calculate heavy quark symmetry breaking in the slopes and curvatures of
the $B\to D^{(*)}\ell\bar\nu$ spectra at zero recoil, including the order
$\alpha_s^2\beta_0$ corrections. We point out that the theoretical
uncertainties in the differences between $B\to D$ and $B\to D^*$ slopes and
curvatures are smaller than in the deviations of the slopes and curvatures
themselves from their infinite mass limits. We find that the central values of
the current experimental results for the difference of the slopes differ from
our calculations when QCD sum rules are used to estimate subleading Isgur-Wise
functions. A better understanding of the shapes of the $B\to
D^{(*)}\ell\bar\nu$ spectra may also help to reduce the error of $|V_{cb}|$
extracted from the zero recoil limit of $B\to D^*\ell\bar\nu$. We argue that
heavy quark symmetry requires that the same fitting procedure be used in the
experimental determinations of the shape parameters and $|V_{cb}|$ from the
$B\to D\ell\bar\nu$ and $B\to D^{*}\ell\bar\nu$ spectra.
