1) How do you change the rear wheel bearings on a Mercedes W124 E280 1994? Can you provide step by step instructions?
2) Is it really difficult without special tools?
3) How long might it take per wheel?
If this was a front wheel drive vehicle, it might be worth your time to try and do this by yourself, but even then you would be working with the brakes as well, which I wouldn't suggest to a beginning mechanic. As this is a rear wheel drive or all wheel drive model of Mercedes car, depending on sub-model designation, I wouldn't even think about doing it yourself.
There are brake tools you are going to need, as well as the possibility of needing to rebuild the rear-end. Now, that isn't likely, but if the bearing has been bad enough, long enough, it may have damaged the internals of the rear drive line.
You aren't likely to know enough to tell if this is the case, judging by the things you asked here.
Please take it in and get the work done by someone with a little experience working on RWD Mercedes cars.
I mean no disrespect, and I admire your passion to DIY but this wouldn't be the project I would start with, unless this is something that isn't a daily driver. That way if you screw things up, it can sit in the garage for weeks or months until you have the money to fix what you break. ;-) Even then, where safety systems like ABS are involved, I would have the work inspected by a certified mechanic before I took it out on the road.
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