JHZR2 and DieselHead,

The gas pressurized shocks have a chamber of gas (Nitrogen, I believe) under pressure that is separated from the oil by a floating piston. The gas pressure pocket serves two purposes, the first is to keep the oil in the shock that has to travel through some small holes to damp out motion of the spring/mass system under enough pressure so that it does not cavitate and become a mixture of gass bubbles and oil. Once the oil becomes a mixture of gasses (that werer in solution when the oil was cold, and that are now out of solution) and oil, its performance in the shock deteriorates rapidly. The pressurized gas chamber also adds some spring force to the system, and this is taken into account in the suspension design. Once the gas leaks out the steel coil springs see more load and the rear sags. If you do not replace the shocks, over time the steel coil springs begin to operate at a more compressed standard length, and they can be damaged so they do not return to their original installed length even with new shocks.

This is definitely a do-it-yourself type job. The rear shocks come in a compressed condition with a kind of tie wrap holding them that way. Don't undo the tie wrap until the shock is in positon as it is not a trivial force and it is not feasible to feed the shock into positon with the shock fully extended. The ones you take out will be readily compressible by hand.

I have had a few problems getting the fasteners off the bottom of the shock in the past. I would recommend that you soak them in a liquid wrench or WD-40 penetrant type oil overnight to make them easier to get out. Overall, the job is not much more complex than removing two 17mm nuts at the top of the shock, and the two fasteners at the bottom, then removing the the old shock. Installation is nearly the reverse, except you get all new rubber parts and hardware with a new set of Bilsteins. So you install some of the new rubber parts and steel parts before you put the new shock in. The rest go in after the shock is in the car.

By the way, what year is your car? I have done this quite a few times on W115 and W123 cars, but not on a W124. I do not know if Mercedes made the W124 car a whole lot different, as the suspension is the multi-link design, not the trailing arm set up of the cars I have worked on. In any case, good luck and I hope this helps. Jim

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Own:
1986 Euro 190E 2.3-16 (291,000 miles),
1998 E300D TurboDiesel, 231,000 miles -purchased with 45,000,
1988 300E 5-speed 252,000 miles,
1983 240D 4-speed, purchased w/136,000, now with 222,000 miles.
2009 ML320CDI Bluetec, 89,000 miles

Owned:
1971 220D (250,000 miles plus, sold to father-in-law),
1975 240D (245,000 miles - died of body rot),
1991 350SD (176,560 miles, weakest Benz I have owned),
1999 C230 Sport (45,400 miles),
1982 240D (321,000 miles, put to sleep)