Abstract: A vehicle, such as a tractor, has a main change-speed gear with an associated clutch and a load shift gear coupled to a selector rod. The load shift gear can be shifted under load between a normal position and an under-speed position which produces increased tractive effort by reducing the speed by about 20%. This load shift gear can be operated by the same lever as operates the main change speed gear. In order to prevent simultaneous operation of the main gear and the load change gear, with corresponding interference with the synchronization of the main gear, an interlock device is provided. The interlock device includes a bellows which is connected into the hydraulic circuit for the clutch and, when the clutch pedal is depressed, the bellows holds a plunger in interlocking engagement with one of two grooves in the selector rod which is mechanically coupled to the load change gear. In other embodiments, a mechanical linkage between the clutch pedal and the interlock device is provided.

Abstract: This invention relates to a shift lever assembly for changing the speed of a power take-off shaft of a tractor. The assembly comprises a movable rod positioned between two different speed positions having a neutral position therebetween. The rod has abutment means secured to it which cooperates with knotched plates so that the rod can be moved in a linear direction between the speed positions only when it is rotated while in the neutral position.