Abstract: A truck transmission jack includes a wheeled base to allow the jack to be moved in position below a transmission, gear box, or the like. A cradle is supported upon the wheeled base for engaging and supporting the underside of a transmission or gear box. The cradle is supported by three support arms, each being pivotally coupled to the wheeled base at one end of each support arm and pivotally coupled to the cradle at the opposing end of each support arm. All of the support arms are parallel to one another for maintaining the cradle in a relatively horizontal position as the support arms pivot. Two of the support arms are elevating arms having coaxial pivot points and extend from opposing sides of the wheeled base. A hydraulic jack rests upon the wheeled base between the elevating arms and includes a piston rod extendable upwardly for raising a yoke that is pivotally coupled to the elevating arms in order to raise the cradle.