IF you are planning on replacing the steering coupler please read this story, it may save your life.
I replaced my 83 380 sl steering coupler and thought everything was OK, drove it for a month or so then we went to Lake Tahoe in the Sierras, hiway 50 with lots of turns and two way traffic areas.
On the way back I stopped at a burger place, while my wife was ordering the food I decided to let the car roll in neutral and drive it into the parking spot closer to the table, the top was down and the car interior was full of stuff.
As I start turning the steering wheel I hear a thonk and the steering wheel starts free wheeling, attached to nothing...I though that the new coupler gave out. Luckily I had a few tools and took the steering apart, I was able to fix it or so I thought and drove home. Next day I took the steering coupler and steering rod out and inspected them. I noticed that the coupler lip was shiny as well as the steering rod end. I realized that the two parts were only making a 64th or less of an inch contact when they came apart and that when I turned the wheel without power steering the rod slipped out of the coupler..
How the hell did I make that mistake! Was my first thought as well as I feeling really lucky!!!
I tried a few times to re install the coupler and came to the realization that the steering rod was not long enough to make a good fit, that the steering rod and gear box have grooves in order to make the correct fit and installing the bolts properly also keeps the rod and coupler from being able to slip out. I was looking at my steering rod and determined that the same design that will keep the steering wheel from impacting the driver in case of an accident was causing the lenght problem.
I was able to extend the length of the steering rod 3 inches and fit the coupler and rod to perfection. I can't figure it out how it became so much shorter that what was actually needed, it probably slipped into itself when I was installing the new coupler and being that you can't see a thing and most of the work was done by touch; what I thought was a proper replacement was actually a death trap. Please be carefull. Hope this info helps keep you safe.