2012 ml350 bluetec already needing new front differential..
 

I'm new to this particular forum, but have been a member for many years to others, and thought it was time to join mbworld, as this it seems to get quite a bit more traffic.

We just replaced our fully optioned 2006 ml500 (which was a rock solid vehicle for us) with a CPO 2012 ml350 bluetec about 6 weeks ago. Since taking delivery of the bluetec, it has been in the shop numerous time for a total of 3 weeks. The 3rd day of ownership it needed the oil cooler replaced. then the drivers seat bottom, 2 nox sensors, subwoofer, headliner replaced, and a couple other "issues". Took it back to dealer yesterday as the check engine light came on again, and I requested the technician drive the vehicle and listen for a faint, but noticeable whine noise that could be heard from the drivetrain while under load. Got the call later in the day that the front diff. is toast. After draining the fluid, they noticed metal shavings and fines in the fluid. Dealer ordered a new one from germany and it should be here sometime next week.

This is all too familiar, as our ml500 had a bad front diff at about the same miles (38k). I really thought that mercedes addressed the bad differntial bearings with the late model w164
and surely with the w166. Hopefully ours is a rare occurrence.

Has anyone else had a differential or oil cooler replaced on their w166 bluetec? Im thankful for the warranty....and cpo after.

Please tell me more about this noise? Is it constant or a woop-woop sound? At low speed or high speed? When slowing down or accelerating? Because I think I am hearing a soft woo-woo noise around 40 mph from the front and I have new Michelin latitude tour hp tires at 12k miles and they are wearing very evenly with minimal wear in the front/rear without any feathering or scalloping.. I am wondering if its a bad wheel bearing.

The noise is constant, but only present on load/acceleration. When you let off the accelerator and coast, the noise goes away. The noise was most noticeable when feathering or light acceleration. Once up to 50mph or more, road noise would drowned out the whine noise and I could no longer hear it. A way to test if it is a wheel bearing or front differential is to drive about 30mph, or fast enough to hear the noise, and shift the vehicle into neutral. If the noise is still present, it is most likely wheel bearing or worn tires.

Ironically, our bluetec had a front passenger wheel bearing go bad right before the front diff. The both made a similar whine sound, but as I mentioned, the front diff sound was only under load. Hope that help.

Hi audimotion,

I did drive it up to 30-40 mph where it makes woo-woo noise. It does not do it at any other speed. It does not change with road surface or going left or right. It does not go away when putting it in neutral. Also the tires are new with 10k miles on them (Michelin Latitude Tour HP) and I personally inspected the front tire and measured inner and outer tread and they are all 8/32th depth without feathering or scalloping that I have seen on cheaper tires that would cause this so call "cupping" sound. I don't have any vibration at any speed related to balance. BUT I feel a slight humm in the steering wheel when the noise comes and goes so I am convinced its a front wheel bearing… Did yours change with left or right lane change at 40 mph?

From your description, its likely to be a wheel bearing. When mine was making noise, I did the gradual lane change to detect more/less noise and could tell a slight difference. If you have a different pitch in noise with lane change or load from side to side, it's most likely a wheel bearing....or a tire may have a broken belt...just another possibility. At least it doesn't sound like it's the front diff.

If a tire had a broken belt wouldn't it vibrate badly at highway speed? The Ml350 is smooth as butter at speeds even up to 90 mph.

Possibly, but I've had broken belts before and car/truck drove fine. From what you have Described, it sure sounds like a wheel bearing. When I had my bearing replaced (about 3 weeks ago), they were on back order. Took a week to get the part...

Audimotion

Sorry for inundating you with many questions. Please tell me more about your broken tire belts. Did you see them or feel them on the tire? Did they do that woo-woo sound at specific low speeds only or had vibration?