Shift mechanism for power transmissions

A shift mechanism for a change-speed gearing in a power transmission unit, comprising a first fork shaft for conducting a first and second shift operation of said gearing, a second fork shaft for conducting a third and fourth shift operation of said gearing, and a third fork shaft for conducting reverse shift operation of said gearing in its forward movement, said fork shafts being arranged in parallel with a reverse idler shaft and an output mainshaft of said change-speed gearing and being slidably supported from the transmission casing of said unit through a shift restriction mechanism in such a manner that any one of said fork shafts is selectively shifted by a shift-and-select lever along the fore-and-aft axis of the vehicle while the remaining fork shafts are locked in their neutral positions, said shift mechanism comprising:

• a reverse drive gear and a reverse output gear on said output mainshaft;
• a first shift head member fixed to said third fork shaft;
• a second shift head member fixed to a rearwardly extended portion of said third fork shaft;
• a shift arm member rotatably supported by said first shift head member at its intermediate portion and pivoted at its one end on a projection of the transmission casing to be swung along said fork shafts in response to axial movement of said third fork shaft;
• a shift fork member slidably mounted on said first fork shaft and being supported by the other end of said shift arm member and receiving thereon a reverse idler gear axially slidable on said reverse idler shaft to shift it toward and away from said reverse drive and output gears;
• a spring loaded movable element slidable within said second shift head member to be pushed inwardly by engagement with said shift-and-select lever;
• and
• a stopper pin integral with said movable element and movable between a first position in which said movable element is apart from said lever and a second position in which said movable element is engaged with said lever, said stopper pin being arranged to face at its outer end to a stationary member in its first position so as to restrict forward movement of said third fork shaft and to be aligned with a recessed portion of said stationary member to permit the forward movement of said third fork shaft.