Abstract: The apparatus positively induces synchronism in at least two lifting jacks. It has an upwardly and downwardly movable carriage, on the lifting jack, a column, a lifting device extending along the column, a first control device to control the lifting device in the "lift" direction, a second control device to control the lifting device in the "lower" direction, a "lift" switch on the main lifting jack, a "lower" switch on the main lifting jack. For each lifting jack, a motor device acts on the lifting device. Along each column there is an equally spaced marking unit, the spacing corresponding to the maximum admissible lift difference between the lifting jacks. Each marking unit has an `ON` zone and an `OFF` zone. Rigidly fixed to each carriage is a tracer for scanning the marker units. Each tracer, is in an electrical switching device, and inhibits the motor device when the tracer is in the `OFF` zone, until such time as the tracer of the carriage which is lagging most behind is also in the `OFF` zone.

Abstract: The apparatus positively induces synchronism in at least two lifting jacks. It has an upwardly and downwardly movable carriage on the lifting jack, a column, a lifting device extending along the column, a first control device to control the lifting device in the "lift" direction, a second control device to control the lifting device in the "lower" direction, a "lift" switch on the main lifting jack, a "lower" switch on the main lifting jack. For each lifting jack, a motor device acts on the lifting device. Along each column there is an equally spaced marking unit, the spacing corresponding to the maximum admissible lift difference between the lifting jacks. Each marking unit has an `ON` zone and an `OFF` zone. Rigidly fixed to each carriage is a tracer for scanning the marker units. Each tracer, is in an electrical switching device, and inhibits the motor device when the tracer is in the `OFF` zone, until such time as the tracer of the carriage which is lagging most behind is also in the `OFF` zone.

Abstract: Onto a rectangular bottom frame a lifting platform is hinged by a parallelogram guiding linkage to move vertically above the bottom frame. Between the lifting platform and the bottom platform an air bellows is fitted. A wedge plate is connected at one edge to the lifting platform to move up and down at that edge with the bottom platform while the opposite edge is drawn back and forth along a guide on the bottom platform. The wedge plate forms one side of the parallelogram and the guide forms a second side. The forward edge of the wedge plate is pivotable with respect to its remainder and cooperates with detents extending from the bottom platform to lock the lifting platform in elevated positions. The device travels on wheels which pass into the bottom platform as the bottom platform is urged to the ground under the weight of the vehicle.