seamus2154

Hey guys starting a different thread for my second issue hoping someone knows what it is? 2018 GLC 300 2wd, 30K, CPO. Truck was adult owned, perfect records and carafax, lightly used. A cream puff. All it needed for CPO was inspection, 4 tires and an alighnment. So did the test drive mostly streets and highway didnt notice it. Then once home noticed when doing errands and parking lot driving any hard right or left turn you hear a humming or rotational noise relating to the speed like a rubbing. When side loaded. Not grinding, or clicking doesnt even sound internal to the rear differential. Sound like its an outside hub near tire. Pads look good, put it on the lift and nothing when spinning tires, nothing rubbing. Only happens when slow and turning hard full turn. ?? Any service bulletins or anyone else experience this?? Thanks for your help

Plutoe

It's lift time. I'd have the wheel bearings checked

seamus2154

It is plausible. The reason I question is that its only 30,000 easy miles, but there is where the sound is to the outside best I can tell. I have an appointment with the dealer we shall see.

Thanks for the input

seamus2154

Dropped it at the dealer today. Asked the service advisor to drive in the parking lot with me so I could demonstrate the sound. He agreed is wasn't normal and thought hubs. I wanted to get ahead of a tech drving the car and the "unable to duplicate issue" being me next problem. He said he has never seen that issue in any Mercedes?? But agreed something is up. He looked up the service and knew the customer of the Truck stating this was a lightly used truck very well cared for. So there is no mystery abuse or issues. We shall see. I'll post results

cyidi

Hi,

Where you able to fix the problem? I have a similar problem in my 2015 C180, and havent been able to diagnose what it is. Only happens when turning, and it sound on the back.

seamus2154

They never did diagnose or have to fix anything. It went away, slowly over a couple of weeks. My thoughts are this: I did change the fluid with a MB spec fluid. It was not MB brand. The fluid that came out with low miles was clean and perfect. No issue to be seen. But after fluid change, did take a little while, the sound went away. Its a year now and no issue. Cant say what caused it, but a fluid change did correct it.

Novichek

Is it possible the diff (I assume you changed diff fluid) was slightly underfilled and you brought the fluid to the correct level when you changed it?

seamus2154

No I dont think so. I have a lift in my garage, so it was a pretty easy fluid change with good visibility . It was not low, but as I said I did use a MB spec fluid and feel that maybe it needed to work in a bit. This is common on posi style rear diffs that have clutch packs and new fluid always need to work in. Don't know if the new fluid was the issue? But the issue dissipated within a couple of weeks. The fluid that came out was like new, so I was very early on the service interval. But I always like to start fresh on a used vehicle CPO or not.

17GLC300

Hello, I am experiencing the same issue. I just recently bought my GLC a few weeks ago. I have brought it back to the dealer already but they cannot duplicate the issue. I even drove with a tech and the noise just wasn’t happening. Sure enough after I left for work the next morning, the humming noise is back when I turn. It only does it a few times then goes away after the 3rd or 4th turn. I have an appointment to just have the fluid changed after I read this thread. I hope it helps and the noise goes away. It’s a very annoying noise, especially for the amount of money I paid for it! Thank you for the info here

seamus2154

Yes, we intitially had a problem duplicating the problem, that I heard everyday. I determined it mostley happened first use, cold. Did it every time. But after a drive to the dealer, it wouldnt happen hot. He called the next morning and it did it cold when they checked it. I was shocked they admitting hearing it. Then after a test drive it stopped doing it. They found no issue. Brakes, bearings, differential, fluid. I did not mention I had changed the fluid. It was a CPO and didnt want to have any documented issue where I touched the car in their opinion. The new fluid seemed to have "worked in" because we are 2 years now and the issue has never come back. It cant' be a major issue or we would be seeing many posts on failed diffs. I think its a slight tolerance, or fluid sensitive, needing to work into the diff.

17GLC300

I made an appointment at a local, reputable repair shop that works on higher end vehicles to change the fluid for me. I also read somewhere else that you can add a friction minimizer but I don’t think I’m going to do that. Just a fluid change to see if that helps. I just recently bought it and the carfax doesn’t say anything about a fluid change. Just the control arms were replaced and brakes and rotors in march of this year. The car is great besides that noise in the morning and when I leave work. After it sits for a bit and I drive it, the noise happens.

seamus2154

There is a specific MB spec for the differential, make sure you use the correct spec fluid. I wouldnt add anything. I would do a fluid change and see where your at. I would also want to see the fluid that came out. If its grayish, glittery, metallic, dark, burnt...they are all indicators depending on mileage. I was around 30K and my fluid was like brand new, it didnt need to be changed, and it wasnt making the humming before i changed it. Good luck. I dont think much is wrong, but I know its annoying.