Trolley jack
A trolley jack is a mobile tool that is used to lift a motor vehicle so that it can be accessed for repairs and maintenance .
A trolley jack usually has two larger fixed rollers and two others that can also be rotated around their vertical axis. This gives the tool its maneuverability . The lifting arm has a plate-shaped receptacle at its end.
Early models of trolley jacks used a chain drive . Modern models are operated hydraulically . A lever is moved up and down to raise it . The jack is maneuvered with the same lever. A valve is opened for lowering . This can be done by turning the operating rod. In the case of inexpensive devices, the rod must be repositioned on the valve axis.
With trolley jacks, individual vehicle components such as engines and transmissions can also be brought into position before assembly.