Gear-shift mechanism for power transmission units

In a gear-shift mechanism for a power transmission unit including input and output shafts supported in parallel to each other from a housing assembly for said unit, an idler shaft supported in parallel with said shafts from said housing assembly, driving and driven gears respectively mounted on said input and output shafts, an idler gear axially slidable on said idler shaft, a fork shaft slidably supported in parallel with said idler shaft from said housing assembly and being operatively connected to a manual shift lever to be selectively shifted from its neutral position to a forward or reverse position, a detent mechanism mounted on said housing assembly for selectively retaining said fork shaft in its neutral and shifted positions under a resilient load acting thereon, a shift head member slidable on said fork shaft, a one-way engagement mechanism for effecting engagement of said shift head member with said fork shaft in axial movement of said fork shaft to and away from its reverse position, and a shift arm member pivoted to the inner wall structure of said housing assembly and linked with said shift head member, and in which said idler gear is carried by said shift arm member to be retained in its neutral position and to be engaged with said driving and driven gears in the axial movement of said fork shaft to its reverse position;

• the improvement wherein one of said shift arm member and said shift head member is provided with means for effecting disengagement of said idler gear from said driving and driven gears under a resilient load less than that acting on said detent mechanism when said shift head member is shifted away from its reverse position to be retained in its neutral position and for effecting engagement of said idler gear with said driving and driven gears under said resilient load when said shift head member is shifted to its reverse position, and wherein at least one of said idler gear, said shift arm member and said shift head member is arranged to abut against a stationary portion in said housing assembly.