I've been lurking on these forums here for a few months now, so I thought I'd do a little write up to give back to this wonderful community of helpful people. Our recently purchased 2005 C320 4Matic had developed a rumbling/grinding noise when making sharp turns at slow speeds. Last week, it turned into a very loud clacking sound. I immediately took the car home and put it in the garage until I had time to look into it. After researching here and other forums it seemed that it could be due to a problem with the fluid in the transfer case and that it could often easily be fixed by (not so) simply changing the oil in the transfer case. I figured that even if the transfer case wasn't the problem, at 82k miles it wouldn't hurt to change the fluid anyway. I fould the WIS document for this procedure as well as the Mercedes Service Bulletin posted by others here. I have attached both documents as well as some pictures of the interesting parts of the procedure.This is what worked for me and my specific car.

Here are the tools I used:

-floor jack with small block of wood
-jack stands
-10mm deep socket with extension (to remove the heat shield)
-16mm socket with extension (for cross member and rubber transmission mount)
-15mm and 17mm open end wrenches (for flex disc)
-small pry bar (to seperate the driveshaft from the transfer case)
-torx E12 and 3/8” universal joint with extension (for lead damper)
-6mm allen bit socket (for drain, fill, and inspection plugs)
-fluid pump to pump the gear oil in through the fill hole
-drain pan to catch fluid
-transaxle fluid (5 liter jug Mercedes part #001989230211) My dealer didn't have this but they were able to get it from another Mercedes Dealer about 100 miles away. Thank you Fresno Mercedes and Bavarian European Motors of Stockton.
-Fenix HL30 headlamp to see what I was working on
-Olympus Micro 4/3 camera


Here is the procedure that I used:

I basically followed the WIS instructions except where noted, and I'll go into detail about my deviations from the instructions.

1. Jack the car and support with jack stands. A lift would be better, but I don't have access to one.
2. I put down a large piece of cardboard on the garage floor to catch any drips.
3. Remove the heat shield (two 10mm nuts).
4. Now, the WIS calls for the drive shaft to be seperated from the transfer case, but I foolishly tried to save time and not do this. I should have just done as WIS directed. More on this later.
5. Support the transfer case with a floor jack and a block of wood.
6. Remove the two 16mm bolts holding the rubber mount to the center of the cross member.
7. Remove the cross member (six 16mm bolts)
8. Remove the rubber mount from the bottom of transfer case (four 16mm bolts).
9. I was hoping to be able to gain access to the fill port (6mm hex) at the top of the transfer case without the job of disconnecting the drive shaft. A 6mm hex socket on a ratchet was much too big to fit in that little space up there. I read that someone on this forum was able to cut down an allen key with a dremel and get it to work. I tried just that. Made a nice clean cut with my dremel. Didn't work for me. There was such a small range of motion for the allen key to turn that I wan't able to get it at the right angle to go into the opening of the plug.
10. So, when all else fails, follow directions. I read the WIS document for disconnecing the drive shaft and then watched a few YouTube videos on replacing a Mercedes flex disc. Having never done this before, I was hesitant. This turned out to be MUCH easier that I had anticipated. A 15mm and 17mm open end wrench was sufficient to loosen the bolts. I was hoping to use the ratcheting box end, but the bolts were too close to the drive shaft so I had to use the open end. This took a little while. Once loose, they were easily removed by hand. With the car in neutral and the parking brake off, I was able to turn the drive shaft and gain access to the other bolts on the flex disc. There are 6 bolts in all on the flex disc. Be sure to remove the three that hold the transfer case to the disc. Not the 3 that hold the disc to the drive shaft. Leave the disc connected to the drive shaft. Then I used a piece of tape to mark the flex disc and the transfer case mount to make sure they matched up correctly. I also kept track of which bolt came out of which hole. Don't want any vibration issues.
11. I used a small pry bar to separate the drive shaft from the transfer case. I suspect a large flat blade screwdriver would work equally well. This also was much easier than I expected. It only moved back a couple inches, but that was all I needed.
12. At this point I lowered the transaxle just an inch or two.
13. I was now able to reach the fill hole with my hex socket and ratchet. I used a 6mm hex socket on a ratchet to break loose the fill hole. Success! Knowing I had access to the fill hole meant I could continue with the job.
14. I used a torx E12 socket to remove the 3 bolts holding the lead vibration damper that blocks access to the inspection hole. With the transaxle lowered slightly, I was able to use a 3/8” universal joint with extension to get at the top bolt. When reinstalling the damper I put the two bottom bolts in first then started the top bolt with my fingers.
15. I drained and refilled twice as per the Mercedes service bulletin. When clean oil stopped coming out of the inspection port the second time, I was ready to reassemble.
16. Reinstall everything and torque to proper spec per WIS.
17. After getting the car down off the jack stands, I drove it around at 45 mph for about 20 miles as directed in the service bulletin.

The procedure was a success. It sounds like new! Not even a hint of any sound or vibration on sharp turns at slow speeds. To say that I'm excited about this would be an understatement. I may do this every few years now just to make sure I don't have any problems in the future. Thanks again to everyone on this site who helped me to do this!

Ken

 

Nice write up!

 

Nice job on this!