1984 300D Knocking sound from right rear wheel area
At the end of a from a trip of about 4 hours, I noticed a very harsh knocking sound coming from the right rear wheel area of my 1984 300D every time I took off from a stop. It sounded like the axle or wheel would fall off. It stopped after I arrived and parked it over night. At the end of the return trip, it started again and continued every time I took off from a stop. The next evening, I got under the car and checked axles, U-joints, drive shaft carrier bearing, wheel bearings, differential oil level and could find nothing definitive. I took the car out for a drive and it would not make the noise again. I have driven it around town for a week and no noise. I guess it only happens after a road trip of 3 plus hours? Any ideas?
Thanks
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Axle or emergency brake
These are two more common reasons for the type of noise you are describing. Remove the rear rotor and look for broken attachment springs on the rear brake shoes. Axles are hard to diagnose. Once you raise the car off the ground the axle will "stretch" and appear to be ok because the joints are not riding in their normal wear points. Sometimes removing the axle and checking play by hand through its full travel is the only way to confirm a problem. You might consider taking it in to a good suspension shop if you have one in your area.
Transmission and Differential Mount
I had very similar issues a few weeks ago. Long trips (30+ minutes on the interstate) would create a very similar sound as to what you describe. My transmission mount was completely gone. It was just a heap of crumbled oil soaked rubber. (fixed it with Kent's Engine mount kit and instructions)
I also changed out the flex disc while I was under there.
However, last week it started making a similar noise but much sooner (i.e. 5 minutes of driving). Turns out to be the inner joint of the rear passenger axle (now being shipped to me) is on its way out. The boot was almost completely torn apart. My Differential mount is also going to be replaced during this procedure since it is coming off anyway.