So recently, we were out locally in the 1970 Trabant 601 limo, about three miles from home accelerating up a slight hill, when suddenly the engine revved up alarmingly, but the car slowed down to a stop. Even more alarming was the nasty grinding noise coming from the engine/transmission. I stopped the engine and freewheeled to a place off the road, and arranged a lift home and fetched my van to tow the Trabi home. Suggestions as to the cause came from the Facebook club. Clutch failure was the favourite. Anyway, subsequent dismantling showed this The clutch parts seemed fine but the flywheel was loose, rocking on its taper even before undoing the 36mm nut. Inspection showed the Woodruff key snapped in two, caused by the last person who serviced the flywheel did not torque it up properly, or use the locking washer properly. Anyway, the nut had come loose through vibration and eventually the stress caused the key to break, causing loss of drive from the engine to the transmission. It seems Woodruff keys aren't used much these days because I had to search the local area stores and garages eventually finding one at a precision engineer's workshop. All fixed now and back on the road.