My '99 ML 320 started to produce sort of humming noise. The problem is, I cannot point exactly where it's coming from. Whether wheel bearings (all of then) or the driveshaft bearing undeaneath. Anybody please can set me straight what it might be?

Thanks.

I forgot to say mileage, she has only 76k.

my money is on the drive shaft bearing. I recently changed mine, at 91k a 98ML. It started with humming, came and gone for a while, then humming persists. The drive shaft bearing grease all dried up and some of the bearing balls are shot.

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98 ML320 (gone but not forgotten)

How difficult to replace is it? I ordered the part already, but not sure yet about the procedure and time it takes for DIY'er.

depends on what you have. If you got a lift, it will be much easier and quicker. I spent a good 4 hours to complete the task mainly because I had to lay under the truck and turn those rusty bolts with limited space.
From loosening the bolts to taking the whole shaft out took me about 1 hours, without using any air tools. The U-joint was stuck and took me another 30 minutes to figure out the long pry bar was my best friend. A 2 prong puller is needed to pull the bearing out of the shaft.
While the shaft is out, check the rear output shaft seal on your transfer case, see if the seal is in good shape. I didn't and after I put everything back, there was a slow leak from that seal. I ended up ordering the seal and had to remove the shaft again to install the seal.

If you have a trusty mechanic, it will probably take 1-1.5 hour to complete the whole job for you.

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98 ML320 (gone but not forgotten)

Thank you for a very helpful hints.
I will work on it next weekend when the part arrives.

supradupe,
Could you post a step by step procedure for replaceing the drive shaft bearing? I have ML320 (02) with 65K miles. My ML has same noise. I replaced center support bearing but the noise still there. The noise seems related to the drive shaft not the wheels. The noise stop when car stop and is most noticeable at about 40mile/h speed driving on a quiet road. Thanks.

did you mark the position of the support before taking it off? it should be positioned such that the front shaft and rear shaft are in a straight line. Also how the shaft attached to the transfer case has to be marked before taking off. You have to reinstall it the way it was coming out of the factory to minimize vibration. shoot me a PM with email address and I can send you the WIS instructions.

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98 ML320 (gone but not forgotten)

Hi, thanks for your reply. I did follow the WIS procedure and marked everything that is required. The drive shaft was put back exactly the same way and position it was before taking off. I found out the U joint was worn. I am going to replace it and see if the noise still coming back. Thanks for your help.

Looking for help with this issue. I had my "center" drive shaft bearing (1634100010) replaced by the dealer at 65K and now with 120K I can hear the noise again. My question is are there both front and rear bearings for the drive shaft? or only one that needs replacing? I plan to do this one myself so any links to detailed instructions would be appreciated.

Thanks!

There are front and rear bearings in the universal joints and a center support bearing.

120k for the u-joints is not unusual if the vehicle has a bad driver.

I'll be sure to let my wife know!!

Perhaps I should have said "aggressive" driver...