Abstract: Structural improvements of a hydraulic four-wheel jack which protects the jack from damage resulting from overloading and/or overpumping, while offering a compact configuration having minimal space requirements. The jack incorporates a hydraulic unit assembly of the piston-and-cylinder variety in which the piston extends in an upwardly direction and bears against a cross-wise shaft being pivotably mounted between parallel cantilever arms, which carry on their respective free ends a lift assembly. The jack further incorporates a base having a unique series of interior passages provided with one-way, spring loaded ball-check-valves, whereby fluid communication is provided for the hydraulics of the jack.