A lot of firsts here: First time poster, first time Mercedes owner, first time changing wheel bearings.
Quick backstory: Bought a 2015 C400 1.5 years ago, immaculately maintained by previous owner, 75K miles….absolutely love the car with one catch. It has more road noise than I think it should. To me, it sounded like a slightly bad bearing- kind of a dull roar coming from the rear that increases in frequency as speed increases. Just this past weekend I replaced both rear bearings, unfortunately did not make a difference. So sadly I probably didn’t help things by replacing the original rear bearings at 110K miles with cheaper TRQ bearings. But, it was a good learning experience- I’m a pretty solid weekend mechanic. My question to you all is, if it’s not the bearings what do you think it might be? What else would cause that worn bearing type sound. It’s definitely not the tires. Is this car known for louder road noise? Thanks for your help in advance!

 

Need to somehow capture the sound for us to decipher. I mean, it could be bad tires, could be the rear differential. If 4MATIC could be transfer case. Could simply be a balancing and alignment issue. So many factors. Try to locate whereabout the sound is in the rear.

 

Thank you for the quick response. I actually do have a recording, I have attached it. I recorded it on my Iphone on voice recorder while driving. It's not great. Please turn your volume all the way up. You can hear the sound best at the very end when I sped up just a bit.

 

I heard two things run-flats and whining rear differential, when was the fluid changed?

 

See if the noise is louder at these specific speeds:https://mbworld.org/forums/c450-c43-...-thoughts.html

 

Sorry for the slow response, work and all...and I really appreciate the help. Thanks for the reference to the other thread. I read thru most of it until someone derailed it talking about brake rotors. Here are some more comments on my scenario both in response to the thread discussion and just attempting to provide more info:

1. The noise coming from the rear is consistent whether accelerating, decelerating, coasting, turning, etc. I can here it around 30 MPH, and then the oscillation gets faster and the noise gets louder the faster I go. The noise never gets deafening, just a background dull roar very similar to when a bearing starts going bad.
2. The previous owner consistently took the car in for the scheduled maintenance visits at the dealer through 80K miles. I don't know if the differential fluid was ever changed.
3. This road noise has been present ever since I bought the car, so not a new development.
4. Doesn't seem to matter if it is hot or cold temperature outside.
5. The tires don't seem to be wearing differently from inside to out. The tires are nearing their end of life, but to abnormal wear patterns.

Hopefully this will help someone guide me towards the next step to diagnose this annoying problem. I would rather avoid taking to the shop, and would like to DIY diagnose for now.

Thanks in advance,

Curt

 

Let me call in an expert on C400s, @TwoC400s

 

Hah, I went out to do some more sound recording this AM with the idea that I would put my mobile phone in the trunk right above the wheels to get a louder recording. I recorded all 4 wheels: RL (trunk left), RR (trunk right), FL (phone in floor left), FR (phone in floor right), and just sitting on center console (CC). To my surprise, the front and CC recordings sounded louder than the rear! Ugh, maybe my problem is in the front after all. I have to admit my hearing is not the best and have never been good with spacial recognition. Guess I will jack up the front and see if I can hear anything wrong with those bearing/tires. Maybe I will even try to run the car on jack stands (very carefully) to see if I can hear/pinoint the nose externally. Anyone got any pother ideas? What a wild goose chase. It would kind of make sense for the bearings to go bad sooner in the front than the rear, but I wouldn't expect either at 110K miles.

 

Do not run on jack stands, that could result in a worse sound! Take to good tire shop for inspection.

 

Best of luck, will also call in @CaliBenzDriver

 

I listened to the MP3 clip... all i heard was a squirrel munching.

You need to take the next step to involve your trusted MB specialist.

Delayed maintenance cost extra... keep up with clean engine/tranny/diff oil, suspensions, control arms, ball joints, ignition tune-up, filters, brakes, tires, engine/tranny mounts & BELT kit at your earliest convenience.

 

I will start with fluid changes if suspected front diff.

 

Another way to go about figuring this enigma is to list all the past maintenance and from there spot what service got neglected according to what's the current mileage: low/high.

100k.Mi can become an expensive target but dies not have to be.

The wrong way to go is trying to be cheap because that will bite you harder later.

Keeping extreme heat under control and sealed cylinders fresh goes a long way to preventing unnecessary heat damages: leaks, coils, injectors, ECM, coolant pipes,...

It doesn't take a genius to see daylight.

common logic is not universal

 

For some reason MB does not have a service interval for front diff fluid, it is apparently "lifetime" MB's lifetime transmission fluid backfired back then.

 

The concept of "lifetime" filled only delivers bad news... delayed maintenance always ends with expensive repairs

 

not sure why MB still insists

 

when the repair cost is greater that bluebook: it's recycle time.

The fair target for lifetime is around 100k.mark.