Looking for some answers here (after searching). I've got a '83 300SD with two stacked ones, an '84 300SD with nothing there, and an '85 300D with an electric contact in place of the switchover valves. What the story? The reason I'm even digging into it is the '83 SD is not shifting into third and beyond, and some seem to think the valves affect the shifting, while others think it's just an EGR issue. If it is affecting anything, how is it being accomplished on the '84 SD where there is nothing there being actuated by the black piece on the linkage?