A manually controlled transmission includes a combined detent and interlock pin mechanism. The elongated interlock pin prevents surrounding shift fork extensions from being engaged when a desired shift fork extension is selected. A recess in the interlock pin allows engagement of a shift lever with a desired shift fork extension, and opposing sides of the interlock pin engage shift finger notches in the other shift fork extensions to prevent their movement. Detent springs attached to the manually controlled transmission substantially contact opposing ends of the sliding interlock pin to provide resistance as an end of the interlock pin substantially contacts the detent spring. An anti-rotate pin positioned proximate to the interlock pin prevents rotation, but not translation, of interlock pin.