Hello all,

I have a 2010 C250 4MATIC Sport (the 2.5L M272 is a Canadian market exclusive) and I have a potential transmission or some other issue with the car. Mileage is 90,000km and I had the transmission serviced at a reputable MB dealer at the 60,000km mark as is mandatory. Looking back I do not believe they drained the torque converter, however. The service was in the summer of 2011. During the early spring of 2013 I had the transmission fluid level checked when the car was in for an oil change because as most of us know MB decided (stupidly and deliberately) to not include a dipstick. They claimed the fluid level was ok.

What is happening is that after driving the car after about 30 mins and having everything warmed up I hear a sublte whistle/whining from the transmission only when I let off of the gas at only two speed ranges and in any gear – 100 down to 90kph and 60 down to 50 kph. The transmission shifts perfectly and no whistle is heard when the car is cold. The noise only appears after everything is warmed up and disappears once any throttle is given. I have also noticed a burning smell when leaving the vehicle after it has been driven at length at higher speeds.

Someone on here suggested that it may be a front or rear differential issue (or transfer case) as the noise is speed specific and is not tied to RPM’s. However, owning the car for several years now I am quite sure this is a transmission noise.

Quite frankly with all the issues people have had with this abomination of a transmission I am very paranoid about having issues with it. I do not drive the car hard and I carefully warm up all the fluids every time I drive the car before driving with any aggressive throttle whatsoever.

If it was my torque converter going, what would be the signs? Should I do another fluid service and get a sample from the transmission/torque converter to analyze? Will a fluid change make any difference?

In addition, I have had new tires installed recently and the techs had to stretch the two rear 225-45R17 onto the rear 245-45R17 to make them fit. The only way I went along with this was I was assured this would work as the tire can be stretched a couple of inches to accommodate a wider rim. I included this as I have heard this can potentially cause weird noises when the car is coasting.

So, any ideas?

Thank you for your time.

 

The TC would cause a high pitched whine that was rev dependant even with the car stationary. Speed dependent noise on overun points to geartrain. Either diff or transfer case.

These cars also have some natural harmonic noise that can show itself in the 100 down to 90 Km/h range. It's very slight but it is there especially if you have a diff that is slightly out on pinion bearing preload. It would be more noticeable with warm & thinned out fluids.

Just monitor it for getting louder. If it remains constant I would not worry.

The 2.5 M272 is a sweet little engine that loves to be revved but at it's lower torque output does not stress the transmission.

Tyre noise will be constant for speed & not effected by overun.

 

I sure know how you are feeling. I had this strange harmonic pitch coming from my shifter around 40-45 MPH but only if I let off the gas or gave it just a little throttle. If I accelerated at a normal rate the noise would never show itself., did not matter what gear I was on. BTW, I have a 08 C300 4Matice (41K miles) so yeah I was a bit paranoid considering all the things I've read on forums.

I took it to the dealer and took a ride with the main tech, he had never heard such a noise before...
He looked at the bulletins and found something concerning the shifter, he made a slight adjustment to mine (he stated he straightened it out a bit) and the noise is 100% gone. The tech was a bit surprised the noise left as well since the adjustment he made was so minor. I believe there was some harmonic sound being amplified/transmitted through my slightly misaligned shifter.

Hope this helps you, if you need additional info let me know and nI will do all I can to get it to you.

 

Thanks for that input. So there is another source of harmonic noise. The slight noise I was talking about is a slight harmonic diffs to chassis/body. No car has perfect NVH engineering & with Benz being quiet cars you are more inclined to hear it.

Frequently with harmonics moving just one frequency out of the critical area will render the harmonic inaudible.