My 70,000 mile car has a loud rear axle whine when you are coasting and most noticeable between 10 and 40 mph. When you get back on the gas it goes away. I disconnected the axle shafts and tried it again with car stationary and it still made noise when going to 2000 rpm and lifting off the gas so I know it’s in the center section. I took the unit out thinking I’ll just get a used one from a junk yard but now that I think about it, isn’t there something I could try and fix first for less money than buying a used piece. A few things I noticed are that the pinion has some play in and out as well as side to side as if the bearing is loose. Also, you can turn the pinion clockwise and counterclockwise when you pull it out, but if you press in on it, it only turns counterclockwise. Any suggestions were to start. I have the WIS service DVD’s but there is no info on internal repairs. Does it mean these are not repairable?

Differentials AREN'T a normal DIYer! IN fact most MB dealer technicians would not touch that type of repair. YOU would be better off finding a used one!

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I got nothing to loose tinkering with it if in the end I get a junkyard rear. Anyway, I drained the fluid and the drain pan shimmered with what looks like gold but I assume is brass. What parts have a lot of brass? Not ring and pinion but bearings? differential? I'll take the rear cover off and dig in tonight.

I have been told that the ring and pinion are adjusted on a sophisticated machine that measures noise and then records the dimension. A collapsible sleeve is set at that dimension. This is not a rear end that can be set by checking the pattern on the teeth. A good used one or maybe a rebuilt from your dealer.