khelms_98

I have a 2010 ML350 4matic with almost 90k miles that has been nearly trouble-free. Recently, I've begun to replace specific maintenance items/fluids since I plan on keeping it for another 3 years or so.

Now on to my potential issue. When I'm driving slowly around a parking lot or down my driveway, when the transmission is holding a low gear to keep from upshifting in a low speed situation, if I quickly let off the gas, I will sometimes get a groaning noise briefly when you can feel the engine braking to slow the vehicle down. I also feel this slightly in the steering wheel. This does not happen regularly enough for the dealer to even attempt to replicate it. So I'm just curious, has anyone else experienced this and is it a problem? If so, with what component? If this happens with all 4matic ML's from time to time, that's fine. I just want to make sure since I am very picky about my vehicles.

I also get a similar groan when accelerating in reverse for the first second or two when I press the accelerator...if I maintain the accelerator position, the noise dissipates but if I let off and then re-engage, I hear it again but only for a couple of seconds. This, also, is accompanied by a very very slight steering wheel tingle (not even bad enough to call vibration).

My transmission has been serviced recently with no metal shavings found at all and I don't really know the signs of front differential failure so I can't say if I suspect that or not. I've spoken to my dealer about changing the fluids in both differentials and the transfer case since he said that might help at my current mileage.

Any help would be appreciated! You've been most helpful in the past. Thanks in advance.

houseofdiesel

My R320 has the same groan at low speed under engine braking, probably the front differential or something I really don't want to know about! It is a common noise among these beasts, not sure why.

khelms_98

That's very comforting...knowing that mine isn't the only one doing this and that it doesn't appear to cause any other issues. I don't get a binding sensation AT ALL even when turning tight and accelerating (ie. quick u-turn) so I'm hoping that means it's not the transfer case.

I'm also going to get all the differential oils changed soon, including the transfer case, and I've heard that smooths things out as well. We'll see.

Thanks for letting me know your 4matic R-class does the same thing! By the way, do you notice when reversing ever?

houseofdiesel

I haven't noticed in reverse, I rarely back up much and not with engine braking needed. I wonder if the engine/powertrain is just moving and something is touching somewhere causing the weird noise, not sure. It does sound like a gear meshing kinda noise like a differential or ?
Diff fluids need to be done once, the transfer case more often it has such a small capacity.

khelms_98

That's good to know...thanks again! I have changed the transmission fluid, brake fluid, etc. so differentials and transfer case are next. I'm hoping to sense a difference even with just a fluid change. I'm going to reluctantly (because of price) let my trusted dealer do it and have them inspect the fluid to see if it's wearing appropriately or if there's an issue that could bring the demise of the diffs or transfer case.

I've heard this noise could be related to the transfer case so maybe if it is beginning to act up, the fluid will tell the tale. Thanks again! If you can think of anything else, please fill me in!

20swrt

Khelms - do your diff and transfer case first. Under normal driving conditions (automatic mode) - your car should not groan when decelerating. You can "force" it to groan in manual mode by quickly choosing a lower gear when decelerating.

FWIW, the diff and transfer case uses different fluids. Unfortunately, the diff and transfer case have a history of failing around 100-170K miles (which is sort of acceptable in German cars nowadays) in earlier w164s. I dont know if its a statistical anomaly because now is about the time they reach 100K+ mi or if it applies to all MBs.

khelms_98

Thanks for the input! I appreciate all of your help! I cannot readily replicate what I'm calling a groan, except for in reverse. But it's done that since I got it.

Oddly, the only times I've really noticed it to the point of any regularity, is when circling the parking lot of my dealer. It occurs when I'm driving slowly and first gear is holding and I let off the gas and engine braking immediately takes over. It's a brief groan that I can hear and slightly feel. I cannot guarantee it will happen every time; it seems to require a perfect sequence of events for it to occur. Because of this, I have never been too worried and it hasn't gotten worse or more frequent.

I will say that I do have a slight, tingling type sensation in the steering wheel that presents itself on the highway. It's not noticeable to most people because they'd assume it's road feel, etc. I notice, however, that the sensation remains exactly the same even when transitioning to a smoother road surface, ie. resurfaced highway. I have thought tires, but they're Dunlops and only a year and a half old.

I'm freaking myself out and I'm also worried that I'm making a big deal out of nothing. I drove a non-4matic 2011 ML350 with 72k miles just for comparison purposes. Road feel and noise was the same, but not as much of the "tingling" steering wheel. The steering wheel was much easier to turn in the 2011 I must say...maybe because of the lack of 4wd components?

Thanks for the help! ANYTHING you guys can suggest would be very much appreciated.

20swrt

Khelms, when the diff gears are manufactured - they tend to be a little noisy at first. But over time and use - they become quiet with normal "forward" use. Going reverse is putting stress on the "other" side of the differential gears. Since the "other" side is hardly used - it is normal to hear more noise from our drivetrain when going in reverse. This is true for all vehicles. Its more of a whine. But that is subjective. Its still best that an expert look at it.

The other reason is this - inside the transmission. http://honda-tech.com/honda-accord-1...verse-1884573/

khelms_98

Thanks once again for your input! That makes sense and makes me feel better about the reverse sound. I'll still probably get transfer case and front diff checked because of the mileage and also the slight "tingling" sensation I feel at speed.

Again, I feel like I'm probably making something out of nothing given that I am super picky about my cars. I'll still get it checked though and provide an update. Do any of you happen to know the going rate for a fluid change for the differentials and transfer case? My local dealer is saying around $150 for each. RBM of Atlanta (not as close as my preferred dealer) charges $55 for each diff and $65 for the transfer case.

Any additional thoughts/comments will still be greatly appreciated!

paulg

If you haven't changed the fluids already, a good investment is a set of magnetic drain
plugs. They are really cheap and obviously easy to fit.

THe magnets will strain particles of worn Diff/bearings etc out of the oil snd stop them slooshing around doing more damage.

Usually, an oil change doesn't make any audible difference, but is VERY likely to extend the component's life.

Not suggesting you get dirty yourself, but I did the oil change in the front diff, installed the Magnetic drain plug and had a tea break, all in about 40 minutes.