  Considering $X(3940)$ and $X(4160)$ as $\eta_c(3S)$ and $\eta_c(4S)$, we
study the productions of $X(3940)$ and $X(4160)$ in exclusive weak decays of
$B_c$ meson by the improved Bethe-Salpeter(B-S) Method. Using the relativistic
B-S equation and Mandelstam formalism, we calculate the corresponding decay
form factors. The predictions of the corresponding branching ratios are:
$Br(B_c^+\to X(3940)e^+\nu_e)$$=1.0\times10^{-4}$ and $Br(B_c^+\to
X(4160)e^+\nu_e)=2.4\times10^{-5}$. That will provide us a new way to observe
the $X(3940)$ and $X(4160)$ in the future, as well as to improve the knowledge
of $B_c$ meson decay.
