The pistons (28,29) which bias the roller support members can be fitted from outside the gearbox housing (1) into the housing where they connect detachably with the roller support members (19,20) also set in the housing. A coupling support member (24) can be inserted into the housing through an end opening in same where it can be fixed in a position at right angles to an axis (O1) of the housing. The main shaft (8) is inserted through an opening (24a) in the coupling support member. The centre parts of the coupling members (21,22) can be swivel supported with the coupling support member and then the drive and output discs are tensioned against each other to form a prefabricated subgroup without the pistons. This subgroup is then inserted through the end opening into the gearbox housing and fixed at right angles to the axis. The pistons can be fitted in the housing from the outside and connected with the roller support members of the subgroup previously inserted.
