Abstract: Stabilization of a truck or tractor for a semi-trailer to eliminate or at least minimize, jarring and vibration of the truck or tractor frame and cab during its operation without load is accomplished by securing a transverse member preferably over a differential housing, to each of the longitudinal truck frame members to bridge the same, and by interposing between the center point on this bridging element, and the top of the differential housing an expandable and contractable air bellows. The truck's pressurized air is connected to this bellows through a manual control valve, preferably in line with an air gauge. A warning indicator may also be connected with the valve to indicate to the truck operator when the air bellows is inflated. Inflation of the air bellows is normally only to be effected when the truck is being operated without load.