Abstract: A bearing support frame (10) is disposed within a rear end portion of a tractor front housing (1) having an open rear end. The frame is secured to internal boss (2c) on a transmission casing (1), which is fastened to the rear of the front housing and has an open front end, and is used for supporting respective one ends of transmission shafts (4, 5, 7, 8) for both of an additional speed change mechanism (6), which is disposed within a rear half of the front housing, and a main speed change mechanism (9) which is disposed within a front half of the transmission casing. An intermediate shaft (17) interposed between the additional and main change mechanisms is also supported by the support frame.The support frame which is preferably composed of front and rear bearing support plates (10A, 10B) facilitates an easy assembly of the change mechanisms.

Abstract: An auxiliary speed change mechanism (10) disposed within a rear portion of a tractor clutch housing (1) is supported by a support frame (11) comprising axially spaced front and rear bearing support plate members (11a, 11b) which are integrally connected by upper and lower connecting plate members (11c, 11d). The change mechanism includes two sets of constant-mesh gears (8, 9, 12, 13) and is operated by a shifter fork (17) which is supported by the support frame through a guide shaft (16). This structure facilitates an easy pre-assembling procedure of the change mechanism which is then installed into the tractor by securing the support frame to a front of a transmission casing (3) to be secured to the rear of the clutch housing. An integral, internal partition wall (1a) is provided in the clutch housing for interrupting lubricant oil for the change mechanism from a main clutch (2) which is disposed within a front end portion of the housing.