  The hadronic weak decays of $\Lambda_c$ are studied in the framework of a
constituent quark model. With the combined analysis of the Cabbibo-favored
processes, $\Lambda_c\to \Lambda\pi^+$, $\Sigma^0\pi^+$ and $\Sigma^+\pi^0$, we
confirm that the non-factorizable transition mechanisms play a crucial role in
the understanding of their compatible branching ratios. We emphasize that the
SU(3) flavor symmetry breaking effects, which is generally at the order of
$1\sim 2\%$, can be amplified by the destructive interferences among the pole
terms in the diagrams with internal conversion. Some contributions are
sensitive to the spatial distribution of the scalar-isoscalar light-quark
sector in the $\Lambda_c$, and its overlap with the light quarks in the final
state hyperon. Namely, a compact diquark configuration is disfavored.
