An adapter composed of front and rear brackets adjustably mounted on a jack pad has an arcuate recess receiving and supporting the rear flange of a transmission or differential housing and a front bracket with an adjustable plate carrying opposed horizontal straps to be bolted to the front end of the differential or transmission housing and recessed to surround the front end. Bolts sliding in elongated slots accommodate lateral and longitudinal adjustments of the brackets on the jack pad and elevation of a vertical plate carried by the front bracket. A feature of the invention is the rigid mounting support provided for the opposed horizontal straps which prevents shifting of the cradled housing and permits all repair work to be accomplished while a transmission or differential is fixedly supported on the jack.