A method permits replacement of components of existing epicyclic gear mechanisms of a wind energy system without having to lift the gear mechanism down from the gondola. In accordance with the method, the housing is divided up alternately in its first parting plane and in its second parting plane and moved apart. The center section of the housing, which includes the internal geared wheel, always remains connected with an adjacent section and therefore does not have to be moved with a hoist. Access to the components to be replaced is always guaranteed by the special method of opening. An installation bolt is also provided that is particularly suitable for implementing the method.