Abstract: A quick-release rack and pinion safety jack assembly for mounting upon the tongue of a conventional trailer. The jack assembly comprises a vertical support stanchion extending upwardly from a rotatable caster, a rigid rack, and a weatherproof box-like gear housing penetrated by the stanchion. A rotatable hand crank is rotated to move the stanchion relative to the gear housing, to elevate or lower the trailer. The internal gear assembly comprises a worm gear driven by the hand crank and a drive gear driven by the worm which selectively meshes or unmeshes with the rack. The drive gear is mounted for rotation upon a rigid axle which penetrates elongated follower slots defined in opposite walls of the gear housing. The drive gear axle is coupled at its ends by rigid links rotatably anchored in a pivotal safety lever. The safety lever is manually deflectable along an arcuate path between a first lock position and a second released position.