Peter,

The ring gear is literally that, a ring with gear teeth on its outer periphery. The ring is pressed on the flywheel, so, if you look at a picture of a flywheel you will see gear teeth on its outer periphery. So, you have to drop the transmission to gain access to the flywheel. I am assuming you are speaking of a 4 speed 240D, so you will also have to remove the clutch hardware to get to the flywheel and replace the ring gear. While you are in there, if the clutch is a few hundred thousand miles old, you might as well replace the wearing parts as sure as can be, once you put those old parts back in, one of them will fail and you will be back inside. More than half the cost if you have someone do this for you is getting access and putting all the removed stuff back on, so it is a significant savings to take care of the clutch while you are there. Good luck and I hope this helps. Jim

__________________
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)