A rotatable ladder rack assembly (10) for use on motor vehicles incorporates an improved lever mechanism (82) for transferring a ladder load from the roof of the vehicle (12) to a location alongside the vehicle and which allows the ladder rack assembly (10) to be used on hi bay vans. A rotatable coupler (92) is journaled for rotation about the ladder rack's connector rod (53) and includes a slot (104) of a predetermined arc length into which fits a pin (106) passing diametrically through the connector rod (53). A lever of the first class is designed to pivot about a fulcrum (76) and the shorter lever arm (L1) is linked to the rotatable coupler (92) for applying a torque to the connector rod (53) via the pin (106).