I have carried out the measurement of the dynamical masses of two known brown dwarf companions HD 984 B and PZ Tel B, and one brown dwarf companion discovered through my survey HIP 21152 B. Dynamical masses of substellar companions offer rare opportunities to test substellar evolutionary models and their underlying assumptions about the formation and thermal evolution of substellar objects. Hipparcos-Gaia accelerations have recently opened up these valuable direct mass measurements for a small sample of long-period planets and brown dwarf companions. Both HD 984 B and PZ Tel B’s dynamical masses are broadly consistent with hot-start evolutionary models. HIP 21152 B has a lower dynamical mass than predicted by models. Gaia DR4 astrometry is poised to improve the precision of these and other dynamical mass measurements.