280SL automatic.

I recently bought a 1976 280SL euro. with an automatic. I did not like the automatic, but the price was right, 2,500, even though it was not running with the timing chain out.The rest of the car was in very good condition inside and out.I After I raplaced the timing chain and ground the valves, 2 were bent. I drove it for a couple months before I discovered that it had 4 speeds, not just 3. It shifted 2 times from start to high, until one day I put the selector in low and discovered that there was another lower gear. It only go's into the lower gear when the selector is in low,then will shift 3 times into drive, giving it 4 speeds. My guestion is, is this normal for the automatic of that time, to start out in second in drive and only start in low when selector is in low postion? This is the first Mercedes that I have owned, so everything about mercedes is new to me.I only wish I had discovered them sooner in my life. Boyd