Ok, so its time for this months repair on my coupe. It has become a ritual of sorts to me. My car likes to spend atleast two days in the shop every month and won't come out till I spend a minimum of 1000 bucks. I think in another couple of months, the mechanic will start setting aside couple of days to fix my car and if I don't call him, he will call to enquire.

So, this time it is the differential. The car has been making loud noise at speeds over 45. Between 45 and 65 it is just unbearable. It is pretty quiet and feels smooth between 30 - 45 mph. Its been like this since I bought it in May this year and finally I showed it to a mech. He said it's got something to do with bad bearings in the differential and quoted 1000 bucks. So I dropped it off at the shop yesterday and he gave me a call today to show the differential. Everything looks fine!!! Nothing wrong with the gear or the bearings, but lot of metal in the oil. He doesn't know where it is coming from, so the genius suggests that I replace the whole differential for 3000 bucks. He said he can put new bearings but can't guarantee that the noise would be fixed. He is going to call me in another hour to give a final quote.

I am thinking of putting in new oil and thats about it. It still is going to cost me 1000 bucks for just taking the differential out, but not going to spend another penny on this white elephant. A bad differential at 60 K miles on a 2002 car? I am sorry, I just lost all respect I had for Mercedes. May be it is not the differential that is at fault, but the list of things that broke down in last 5 months and the list of things that the previous owner got fixed in 4 years she owned makes me believe that C class is really cheap class. I will trade it in for something else and take 4000 loss for the 5 months I owned it. My next car would be anything but a Mercedes.

 

It's probably not the differential. You should have the CV axles inspected. The CV joint in the rear may be the culprit in this case. There are bearings which can start to make noise if the CV joint wears out, or if the rubber boot becomes damaged. If the CV axles are damaged, then you can have them rebuilt at a much lower cost than replacement.

Edit: I almost forgot to mention that I may put my stock CV axles up for sale next week. I just had it replaced yesterday with a C32 differential and rebuilt C32 axles plus a Quaife LSD.

 

You mentioned that there was a lot of metal in the oil. High miles and a lustre of brass is not uncommon, but any chunky bits means you've got trouble. You might have already moved ahead, but it doesn't sound as though you have the right mechanic for this job. Also, you should look for a used rear end. They should last 150k minimum, so a used one will see you through the next few years. On my previous car, a 7 series BMW, I bought a junk yard (they're called recyclers now, but they'll always be junk yards to me) rear end for a couple hundred and put it in myself. It's not very difficult and at the same time you can change and lube the CV joints.

 

Blown diff's is pretty common on the 2002 cars. Its usually the spider gears. Mine went out at 23K. Don't put the diff back in unless youre sure everything is in perfect shape. Check the spline shafts. CV joints will make noise at any speed. Usually in the turns you can identify which side its coming from.