The photodissociation dynamics of the Ar₂HBr van der Waals molecule is studied using the multiconfiguration time-dependent Hartree method. Standard Jacobian coordinates are used to describe the molecule. Two four-dimensional calculations are carried out where the rotation of the Ar₂ molecule and, in addition, either the vibration of Ar₂-Br or that of Ar₂ are frozen. The time-evolution of the probability density in the different modes and the calculation of the dissociative flux show that the dissociating hydrogen atom preferentially moves out of the plane defined by Ar₂ and Br. A comprehensive study of the cage effect in the process is presented.