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2003 SL500, 2012 E350 4Matic P2
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840 Posts
Discussion Starter #1 (Edited)
Having posted on Benzworld several times about an annoying whining noise coming from the rear, I finally got up the courage and replaced the rear Differential.

Brief sequence of events follows:

Originally, I discounted the differential as being the source of the noise because I had not read a single post here or on any of the other forums of anyone replacing a differential. The general consensus is that they are “robust”, bullet proof and rarely fail. Well, they may be all that, but in my case, an internal bearing or gear set did begin to fail and was emitting a whine under load between 45 and 60 MPH. I purchased the car with just shy of 96K miles and from then until now (112K miles) the noise has remained the same with no increase in loudness but getting more annoying by the minute none the less!

I began to suspect the driveshaft center support bearing as the culprit and with the help of Benzworld member oceanliner in one of his posts. I dropped the exhaust and went about the chore of changing the center support bearing. In my opinion, the bearing was free and smooth and not bad but I changed it anyway along with the support bracket just for safety. (It’s called mission creep; you’ll know it well after doing a few simple jobs on your love interest!)

I reassembled everything and went for a test drive. The whiny noise was still there but I had acquired a new problem which was a vibration beginning at about 70 MPH. When I disassembled the driveshaft, I had not marked the two halves when pulling it apart so the halves were not in phase during my reassembly. I pulled the exhaust down again and removed the drive shaft to have it balanced and phased. I got the driveshaft back from the shop and reassembled everything with it now perfectly balanced and phased. The vibration was mostly gone but still slightly there and of course, the whining was becoming even more annoying.

As a side note during all this drama, I had already changed the fluid once using Mobil 1 75W-90 and drove for 600 miles then changed again to 75W-140 Royal Purple which seemed subjectively to quiet it down a little,(... but not really).

In summary, if you should ever have to pull down your driveshaft for any reason, be sure to clearly mark each half with paint. For an interesting and informative read on driveline research, see Benzworld posts by Benzworld member ricebubbles on the subject. (He has been on a mission!)

It was now time to take the next step and change out the differential which is the most obvious culprit of the three moving components in the rear, ie, the differential and two axle shafts. I called my driveshaft shop and told him about my slight vibration and the whining noise from the differential and that I would have the shaft out once again and could he check it for balance. He said that the noise coming from the differential could be transmitting back through the driveshaft as a vibration similar to a tuning fork. Based on that conversation, I decided to forgo another balance check as he assured me that he had spun the shaft up to 10,000 RPM’s and added weights to balance accordingly. So time to bite the bullet and begin to finally solve the real problem.

So I started shopping for a replacement Differential on eBay. I found this low mileage 2002 organ donor and was able to acquire the differential for only $220 including shipping from Pam’s Auto in Minnesota. The box weighed 102 lbs so a real bargain I thought!


Die Seele kann nun wieder nach Hause nach Deutschland gebracht, um in Frieden ruhen. (The soul can now be returned home to Germany to RIP.)

57K! Hardly broken in!


Box arrived………………..


And opened………………..


Inspected for part number match and they do……………….

Received from Pam’s……………


My original....................


All good so far………………….

Car is up on jack stands and a set of ramps. Exhaust system is pulled down and rolled out. Now you’re looking at the problem…………………….


Only three mounting points to deal with and 12 axle shaft bolts, 6 on each side……………


I began by unbolting the drive shaft from the differential and secured it with a bungee out of the way. You do have to loosen the center driveshaft support to be able to push it far enough forward to get the centering sleeve off the locating alignment pin. I removed one bolt and just left the other one loose but snug.


At this point, I began to disassemble the axle shafts. At the time that I began disassembly, I did not have a copy of the “WIS” instruction and had to rely on my memory only having read through it once before, (I will attach a PDF copy to this write-up). I finally was able to obtain a copy which gives the torque specs. Those specs are absolutely necessary for putting it all back to together properly. Step #3 states to bring axle shafts into approximate horizontal position. The wheels are drooping to the max being up on jack stands so the axle shafts angle down quite a bit. Having them straighter really helps in the reassembly. (I used my slim floor jack to get under the wheels to jack them up when reassembling.)

The axle shaft bolts have a Star E12 head and are very tight; torque specs are 70nm so I used an impact wrench to get them broken loose then spun or ratcheted them out. Again, the axle shaft angle made it more difficult. Caution, make very sure that you are able to fully engage the Star bit on the bolt head. I had one bolt that wanted to spit the bit off and round the head. I had visions of having to cut that one bolt off with a cutoff wheel so be alert.

Once the shafts are unbolted, they sort of roll up and out of the housing. Hard to explain but they did not present any problems getting them out and up. I used bungee cords to hold them up and out of the way.

Axle shaft rolled out…………………..


And another view...............


Now the fun begins! I built a simple platform out of wood and bolted it to my slim floor jack. I built it to cradle the differential, but putting the differential into the cradle caused it to tip forward. So I turned the cradle 90 degrees which then held the diff more level. That is how I used it to drop the old diff out and install the new diff. It actually worked perfectly that way. You do have be alert and steady the diff to keep it from falling of the platform but my jack has an easy up and down motion to it with no jerking so all in all pretty safe.


Moment of truth, ready to roll the jack under the diff and remove the mounting bolts…………….

(Please excuse the mess.)

Jack at the ready………………



And another view…………….


Left mounting bracket bolt (DS)……………..


And right side mounting bolt………………………


Front mounting Point……………………


And rear view of left side nut attaching the mounting plate to the rear axle carrier………………….


Notice the paint spot marking. This corresponds to the torque setting specs in the WIS instructions. You’ll see the paint markings Yellow for one spec, Silver and Blue for another. They have made it almost fool proof.

Now remove the three mounting bolts with the jack in position just snugged up to the diff. I removed the front mounting bolt last and that worked good for me.

Now carefully lower a bit……………………


A little more..........................


And out.....................


Finally on the bench old and new side by side………………………..


At this point a word of caution These units are very heavy and probably weigh in access of 80 lbs so don’t risk injury by lifting or having them fall on your foot. Get help if possible!

I used this opportunity to wire brush some of the rust and flaking paint from the new diff. I then drained the old fluid which no doubt was the original and 11 years old. (You can get a complete drain on the bench by laying it on its side.) I cleaned and spray painted. I also cleaned the axle shaft mounting holes out with a thread restorer tool to get rid of the thread lock material left by the original bolts. I also cleaned the axle shaft mounting faces with a stone as well. I then transferred the mounting plate bracket to the new diff and leveled it out to fill with fresh Mobil 1 70W-90.




Fill with fresh fluid and reinstall fill plug.

Okay. All the bench work is done. Now just reverse the procedure. Put the cleaned-up diff onto the jack platform and reinstall. I didn’t run in to any snags. I just raised the new diff into position, jiggled a little here and there and in it went. The bolt holes in the axle carrier did the alignment on the mounting plate. I didn’t fully tighten anything until it was completely snug on the front mount. Once I was certain that I was not going to tighten any stress into anything, I snugged everything up and began the torque procedure at the diff mounting points. The axle shafts went back together very easily. I did jack up the wheel on each side to level out the shaft which made the difference. I did use thread lock compound on all threads during reassembly

To recap and what I would do differently the next time:
I would make sure I had the car at least 18-20” off the floor. I used ramps on the front for this repair which only allowed about 16” of clearance. I usually use stands on all four sides but this time I talked myself into using ramps on the front. You really do need the extra clearance to clear the down pipes on the exhaust system when dragging it out through the rear. I did have to wiggle the diff to get it out from under the rear also, although if my jack platform had of been a little thinner then that would not have been a problem.

All in all, not a real difficult job to do for the DIYers. Just normal tools are needed with a Star female socket set. I have air tools but you could use a breaker bar on the axle shaft bolts and do just as well but slower. I always dread pulling the exhaust system down. This makes three times that I have had to remove it. It is so cumbersome to handle and snake those down pipes back up and not damage the two forward O2 sensors! (Those who have R&R’d their exhaust system know what I’m talking about!). I am also fearful of getting a leak at the manifold where the down pipes connect. I’ve been careful though to watch the collar alignment and has not been an issue so far.

In conclusion, the whining noise is now gone!! What a relief. I was on the verge of just getting rid of the car but now I will keep it for a while longer. The vibration is completely gone so the driveshaft shop was right. I am happy at last! Now on to the cosmetics and little nuisances such as passenger side soft close not working, sun visor repair etc. The little things now!!
 

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2009 E350 4M Avant Garde, My Mistress 2002 S600, Wife 2014 C300 4M Avant Garde with AMG
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973 Posts
Outstanding!

Congrats on your successful job!
This is the kind of forum contribution that makes all of us keep faith in keeping our cars, because we know, if we have to do it one day, someone has done it before and we will know with confidence on how to do it!
 

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W221 & Audio Moderator
2013 S550
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10,928 Posts
Thanks for this, mercy-me! Added to the Encyclopedia.

The first thing I usually recommend when checking for a whiny noise in the back is to let one's mother-in-law out of the trunk. ;)
 

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Registered
2009 E350 4M Avant Garde, My Mistress 2002 S600, Wife 2014 C300 4M Avant Garde with AMG
Joined
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973 Posts
Thanks for this, mercy-me! Added to the Encyclopedia.

The first thing I usually recommend when checking for a whiny noise in the back is to let one's mother-in-law out of the trunk. ;)
Hehehe Warren: All she has to do is push that flashing trunk release button!!!

(MB obviously thought of mothers-in-law locked in the trunk!
 
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