Abstract: A transmission assembly for a hydrostatically or electrically propelled vehicle, comprising an input shaft, an output shaft, a first pair of gears and a second pair of gears, a synchroniser, a hydraulically operated actuator of the synchroniser which comprises a rod, and a hydraulic circuit for moving the rod, wherein the rod comprises an enlarged portion that is slidingly and sealingly housed in a respective portion of the seat so as to define two intermediate chambers. The actuator further comprises a contact element that is slidingly and sealingly housed in a relevant seat that is adjacent to the portion of the sliding seat so as to define a first end chamber, the contact element being able to move independently of the rod and defining an end point of the rod. A second end chamber is defined in an end of the rod that is opposite the enlarged portion.