  A major hurdle for modified gravity theories is to explain the dynamics of
galaxy clusters. A case is made for a generalized gravitational theory called
Scalar-Tensor-Vector-Gravity (STVG) or MOG (modified gravity) to explain
merging cluster dynamics. The paper presents the results of a re-analysis of
the Bullet Cluster, as well as an analysis of the Train Wreck Cluster in the
weak gravitational field limit without dark matter. The King-$\beta$ model is
used to fit the X-ray data of both clusters, and the $\kappa$-maps are computed
using the parameters of this fit. The amount of galaxies in the clusters is
estimated by subtracting the predicted $\kappa$-map from the $\kappa$-map data.
The estimate for the Bullet Cluster is that $14.1\%$ of the cluster is composed
of galaxies. For the Train Wreck Cluster, if the Jee et al. data are used,
$25.7\%$ of the cluster is composed of galaxies. The baryon matter in the
galaxies and the enhanced strength of gravitation in MOG, shift the lensing
peaks making them offset from the gas. The work demonstrates that this
generalized gravitational theory can explain merging cluster dynamics without
dark matter.
