I have a 2012 E350 wagon. The existing brake rotors were eaten up and glazed over on the inside in the front so I replaced them with Power Stop brand rotors and pads. It stops a lot better but the noise is still there. It isn't exactly a howl but more like a grinding metal on metal rotational noise but with a little lube thrown in, kind of like how a bearing sounds when it is going out. The car only has 88k miles on it and was inspected by MB less than a month ago.

Here are the symptoms or otherwise things I've noticed before and after replacing the rotors.

1) The noise starts at about 5 mph and doesn't stop until its too loud to notice it anymore, about 80+ mph.
2) The noise changes by about half an octave when braking, but is for all intents and purposes the same noise as before braking.
3) The noise changes with RPM, as in it gets louder. Pitch/octave is approximately the same across all rotational speeds of the wheels.
4) The noise does not change when turning hard left or right.
5) The wheels do not rock with hands at 0 and 180 on the tire.
6) Brakes feel somewhat spongy in the fact they give quite a bit before biting down on the pads.
7) After driving several miles and coming to a complete stop by rolling only, the front rotors read 160F temperature and the rear ones read 115F. Both evenly.
8) With both wheels supports off the ground, each wheel is very hard to turn independently once it rotates past about 30 degrees or rotation. I would estimate it takes 50-60 ft lbs or torque to turn the wheels by hand. The wheels counter rotate like an open differential would.

I'm truly lost on this one. My only guess is I let in a smidgen of air while cracking open the bleed screw to push the caliper pistons back. Otherwise I just want to make sure nothing is wrong with the differential because the wheels shouldn't be so hard to turn, or should they? Any thoughts?

 

Well, since you mentioned a bearing noise, it's possible you have a bearing going bad in your transfer case portion of the transmission. MB fix is to replace the transmission in it's entirety. Let's hope that is not it. May be worth a paid diagnosis at the dealer.

 

could be bearings/gear in front diff...based on sound changing when braking(different load on the gears) seems the most likely.

can you hear the noise when rotating the wheels when the car is up in the air? maybe put on jack stands with all tires off the ground, put in gear and allow wheels to turn while idling only(might have to put in "Dyno Mode" to avoid errors in traction control system

did you do brake work yourself? Did you replace the brake hardware(slides)? Grease the pins and check for corrosion? could be hardware is not allowing brakes to completely release(fairly unlikely due to low/even brake temps after stopping).

could be tires as well(also pretty unlikely by the "bearing noise" you described, but entirely possible...)???

 

I don't think its the differential.

Not only because I don't want it to be, but the sound is from something of a significant diameter like a rotor or a tire. Unless the transfer case bearings are six inches in diameter I don't believe it is the culprit.

 

At 88K and since MB just looked at it, we can assume you have had the transmission service completed?

 

No they just did a 2 hour inspection to ensure there were no mechanical or electrical issues with the car. It would be cool if all I had to do was replace the fluid and filter though

 

Well, you are way past the interval if that is the case. I would start there and get that done if there is no record.

 

I did a quick search but I’m on mobile and didn’t find much. Can you please link a write up on transmission fluid and filters? I know there are acceptable dealer alternatives of paying $30/quart for ATF.

 

https://mbworld.org/forums/c-class-w...ce-thread.html

I personally, do not have the tools or skill to do transmission work on a Mercedes. Any other Brand, no problem. Good luck!

 

Thank you. It was pretty straightforward in my '95 E300 and 04' E320. Drain and drop the pan, replace the filter and gasket, put it back on, and fill it back up with transmission fluid. Is it more nuanced in this model?

 

Yeah, you have to pump the fluid up through the drain hole, heat it up to a certain point (need a scanner), then drain the remainder. You also pull the drain plug on the torque converter. I've done it and as long as you have the proper tools it's not terrible. I got everything I needed from FCP Euro. It's definitely more of a pain than any other car I've worked on. Have a look through the procedure and post back with any questions on it.

 

In point 3 you say that the noise gets louder with speed but the pitch stays about the same. Usually all drive components, tires, wheels, C.V. joints, bearings etc. change pitch up with higher speed but there is one component that gives kind of the same pitch with different speeds. This is the drive shaft from gearbox to differential. It gives a humming noise which I believe is actually the natural vibration of the car body around the shaft and that frequency does not change.

 

Hmmm, does that shaft have C/V or U-Joints in it? I'm not familiar...

 

My bet is the transmission is failing. Please return and let us know how it goes.

 

haha thanks man I appreciate you planting this seed.

I'm going to change all of the driveline fluids and go from there.

 

Just trying to get you back into your own thread to comment, and it worked. Good luck!

 

Okay I changed the transmission fluid and the engine oil.

The issue persists. In fact I put three different sets of pads on it. Every single time they started quiet then got progressively louder. Also the clips on the inner pad to hold it onto the caliper piston seem to be snapping off and it just sits there and slaps around.

The last thing I can think of that might have done this was I mixed up the caliper mounting brackets when cleaning them on a bench. However, when I look this part up online it seems as though it is ambidextrous.

I know this is a brake issue now because if I start off slowly enough I can make the brakes create a droning noise, similar to a wet finger stroking the rim of a wine glass. When I even touch the brake pedal it goes away. What the heck is going on here.

 

floating calipers, right? Do you have a slide pin or hardware issue of some kind? maybe the rotors have something between themselves and the hub, causing an issue? The pad clip snapping off seems to indicate some undue force putting something into a bind, especially if it happened more than once