  For any positive integer $N$, we prove that the rational torsion subgroup of
$J_0(N)$ agrees with its rational cuspidal subgroups up to a factor of
$6N\prod_{p\mid N}(p^2-1)$. Moreover, for modular Jacobians of the form
$J_0(DC)$ with $D$ a positive square-free integer and $C$ any positive divisor
of $D$, we prove that the $\psi$-part of the torsion subgroup of $J_0(DC)$
agrees with the $\psi$-part of its cuspidal subgroup up to a factor of
$6D\prod_{p\mid D}(p^2-1)$, where $\psi$ is any quadratic character of
conductor dividing $C$.
