I second the advise on using a Haynes manual. My 123 is a TD so the shock replacement is a different animal. My first Benz was a 116 chassis SD with regular shock in the back. I believe you will need a 17 mm wrench, a pair of vise grips to hold the center shaft from turning while you loosen the nut. You want to remove the upper nut first. Then jack the car up until the wheel is free to spin, remove wheel. Now this is what I ahd to do to get the shocks out from the 116. There are 2 bolts at the bottom of the "A" arm, once those are loose, the shock will drop down, but you will find that there isn't any clearance to pull the fully expanded shock through the hole in the A arm. So what I had to do was lower in the car onto a jackstand, then place your floor jack under the hub and jack it up, compressing the spring, minding the shock, until there is enough room to pull the shock through. For installing the new shock you slide it through the hole in the A arm and slowly lower the A arm down so that you can put the lower bolts in. With that done, slowly raise it up again to get the shaft through the hole at the top. Put the new bolts on, up top with the shock fully seated. Put your wheel back on and your good to go.
1994 MB E320 Coupe (199,500 mi)
1992 MB 190E 2.6 (173,000 mi)
1983 Porsche 911SC (148,000 mi)
2004 Volvo V70 2.5T (198,000 mi)
President of CT/Westchester Section