Truck is about to hit 300,000km (approx 295k I think). About a month ago I started to hear a differential and/or wheel bearing noise.

Took some sharp bends on the highway at higher speeds (70mph or about 120km/h) and the noise doesn't change. So I assume it isn't wheel bearings because the sound is constant based on speed of the truck, not on which wheel has less or more weight on it.

So figured it is the front or rear differential. No idea which one.

Have read the horror stories of front differentials failing on these trucks and needing all new bearings. Apparently the bearings fail and when you drain the diff you get metal shavings (or even silver coloured fluid with metal bits suspended in the fluid)

I figured I'd drain/fill the front first, drive the truck, then do the back. That would give me an idea of which one is causing the problem.

VERY easy to do in these trucks. Raise the truck with Airmatic (easy!) or jack it up (harder). Remember Airmatic only lifts the truck 4" so you can even get some ramps or possibly two flat 2x8 boards under each of the four tires and you should be good.

Crawl under the truck, remove the belly pan cover (the rearward one, not the front one) and open the fill plug (first!) then the drain plug.

I measured my fluid and it was approx 950ml. The capacity is 1.1L (1100ml). So it was low but I figured not enough to make a difference. Fluid was the color of Coca-Cola and new is the colour of maple syrup, so it looked old. Smelled worse than the new fluid (not necessarily burnt, but more of a "completely worn out" smell if that makes sense).

NO metal particles at all. Just really dirty fluid.

Use Febi fluid.. it's called "Hydraulic-Getreibeol" (Hydraulic Gear Oil in English). Much cheaper than the MB stuff and meets all the proper specifications.

You need 2 liters because capacity is 1.1L. I didn't measure but definitely used more than that. I'd estimate that I put back in somewhere between 1200-1350ml.

So the differential has about 250-400ml more fluid now than before.

Howling is GONE! Glad I didn't drive further before changing this fluid.

There is NO service interval but for the cheap cost of the fluid, change yours NOW unless you know exactly when it was done before. I'll be doing the rear this weekend too.

Handy tip: don't use those 'soap dispenser' type pumps. They don't fit the bottles and I counted 15-16 pumps to just move 100ml of fluid. So I would have to pump 200x which sucks when you are under the car

Go to Princess Auto (Canada, $10) or Harbor Freight (US, $6) and buy an oil suction gun. The plastic version is fine. Capacity is just under 1/2 liter.

Filled it and pumped into the differential 3x and I was done. Dribbled out, put the plug back in, and all is good.

30 min job includes a quick test drive, removing/installing belly pans, etc.

The first time you do it may take longer (and if you have to jack up the truck that takes time). But Airmatic and if I have to go do both, I can probably do it in an hour total for front/back.

 

Have always changed the differential fluid with each transmission service - every 40,000 miles.

 

Very lucky indeed!
For those not so lucky, check out benzexpert.com.
They've got the complete bearings kits.

 

Thanks for the info. I plan to do mine this week. Any tips of how to get airmatic to stay at the highest setting when you turn off the car? If I use ramps for the rear will it auto level? Do I need to be completely flat? Thanks.

 

Will do mine ML63 in next few days, i got humming noise on my front as well. Hope its the oil not the bearings. What gear oil to use on diffs and transfer case? Usually use Mobil 1

 

I personally went with royal purple 75w90, I read on some of the other AMG boards you can run it. Plus I'm in Texas so the slightly different weighting is fine, instead of the 75w85 which is stock. I need to order another bottle to do my front diff. I don't recommend the hand pumps, its a huge pain to do. I need to get a electric one. I still have the sound, I'm not sure what it is, maybes its actually coming from my front.

 

Royal purple $23 Mobil1 $13 i picked Mobil1 75/90 Dont believe that oil can be $10 diff in price and be twice as good. i think its more paying for the brand. Maybe i am wrong, dont know.
Check your Transfer case to make sure you got oil in there, drained mine todaygot very little oil outand suspecting it was my humming noise. Felt like wheel bearing. Will refill next 2 days and find out if it was my problem, if i am lucky that low oil didnt mess up my transfer case

 

thanks, I’ll maybe change it tomorrow. Has there been any change in noise for you yet?

 

Filled it up last night and it about half a quart i guess it was right. Didnt drive it yet to feel if noise went away. Will let you know in next few days. But now i know that both diffs and transfer case got fresh fluid.
Sorry for false alarm, very surprised that it takes only half of quart

 

Drove my car today still humming noise.Front diff, rear diff and transfer case oil changed. Today i jacked up the front, put it in D and let front wheels spin didn't hear any noise.
Made me think that humming noise coming from center bearing on the driveshaft. Unless front diff or wheel bearings have to be under load to make noise.
Very annoyed with that sound, feels like i am driving a KIA not a MB.

 

Thanks for the update, yeah the noise has been annoying me too. If its not causing damage I guess I can live with it.

 

I finally replaced my front fluid last night. I gave it a drive today and honestly I think it improved the noise quite a bit. The hum seems to be greatly reduced, there was just some slight flakes on the plug cap, not very much though. The fluid was dark brown but not black. There is still a little hum but it sounds more like tire noise now. Its weird because the noise sounded like it was from the rear, but I guess the front driveline transmitted the noise. All in all, I can live with what I have now. I also got a icarsoft in the mail today, so its helping me diagnose random suspension malfunctions. I'll probably tackle the transfer case as well, but I don't have the best perfectly level area at my house to do thet one, since I live on a hill.

 

I think mine is front wheel bearings or driveshaft center bearing. got105k miles on it now i wonder when front bearings go bad, or center bearing go bad on this car? its very hard to figure out where the sound come from. looks like my humming noise is the loudest about 45 to 55 mpg.

 

Wheel bearings can be easily diagnosed. Drive the vehicle on a straight, smooth road at the speed where you hear the loudest humming.

With no vehicles near you, and firmly in control of the vehicle, steer left and right inside your lane gradually but firmly, several times. If you hear changes in the humming sound, a wheel bearing or bearings can be the culprit. The loudest noise will come from the bearing which has the heaviest loading, which is on the opposite site to which you are steering. Very easy.

Another wheel bearing test for more advanced failures (worn bearings) is to notice if the sound changes with vehicle speed. For example, decelerate with no brakes applied (coast) and listen to the sound. If the sound changes while decelerating with no brakes on a straight, smooth road, wheel bearings are suspect.

Drivetrain (e.g. center bearing) humming is very easy to diagnose. Drive the car on a straight, smooth road at the speed which the sound is loudest. Do not use cruse control, but rather keep your foot steadily on the accelerator pedal. Notice the noise intently. Then lift your foot off the accelerator pedal, and decelerate a few mph/kmh. Then put your foot back on the accelerator and accelerate to the original speed, where the sound was loudest. This is called tipping into and out of the accelerator. If the sound changes during tip in/out, you have worn drivetrain component(s), likely in the main propshaft.

After you do these tests, please report back. There are other drivetrain tests to dig deeper into which shaft and which joint(s) are the problem(s).

 

Regarding the original post, I agree with changing axle oil, in fact changing all oil is necessary for high mileage operation.

M-B indeed does not specify GL/GLS/ML/GLE axle or transfer case oil change intervals, although oil change is required for high mileage operation.

I think 100,000 miles/160,000 kms is a good interval for this. This is based on 40 years of motoring and 1 million miles of vehicle operating combined experience.

Strangely, M-B does not recommend replacing the poly-v belt. To me this is another good 100k mile service item.

M-B is one of the few carmakers that spells out a service interval for transmission oil change. Many (most?) carmakers and their dealers are spewing the "sealed for life" nonsense story. 100,000 miles / 160,000 kms is the longest I suggest driving without transmission oil change. M-B spells out 6 years / 60,000 milles which is nice.

 

Will do the steps you said after i go my left intake camshaft and followers. Plus i took the intake manifold, will clean up real good and do the spark plugs. Then i start looking in to the humming noice.
anyone knows torque spect and order how to torque bolts Manifold to the block?
Thank you!

 

2010 ML 350

I changed my front and rear differential fluid this weekend. It wasn't that bad. I didn't even jack up the car. I drove the car up on two 2x6 pieces of wood stacked on top of each other which allowed me just enough clearance to get the job done.

I used 75w-90 valvoline synthetic for the differential and Shell 134 tranny fluid for the transfer case.

Transfer case fluid was black. Differential fluid was black/brown.

 

I have changed all of my wheel bearings at approx 120k miles on my 2008 GL550 and on my 2011 GL550 front wheel bearings at 76k miles. The fronts as described already can be determined by turning .. the rears not as easy . The fronts are a little easier to change than the rears (emergency brake cables ). I find it much easier to work with a press and definitely a wheel bearing harbour kit. Also for first timers check your magnetic wheel .. there are a few brands that have both sides of the bearings with magnetic wheels so no mistakes of wrong side installs.