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Discussion Starter #1 (Edited)
Hello folks,

As some of you may know, I've been grappling with this issue on my 1994 E320 for quite some time now, and I've managed to get some ways ahead in quelling some of it off, but so far I haven't been able to get rid of it entirely.

By "better" I mean that the vibration is now less severe, and starts to appear at higher speeds (it starts to get really noticeable - and annoying - at about 150km/h, but now not nearly as unbearable as it used to be.)

Generally speaking, it starts as a faint "rubbing" sensation, then develops into a resonating throbbing in the floor pan right under my left foot (when it's not on the dead pedal) and in the backrest of the driver's seat, along with a very slight wobble in the steering wheel, and then at higher speeds, it escalates into a vibration that seems to engulf the entire car.

Here's what I've done so far, in (a rather rough) chronological order:

- First off, when I first bought the car almost four years ago, I had replaced the OEM 15" wheels with (cheap) aftermarket 16" AMG replicas so I could run tires rated higher than H. At the time I thought that the vibration was caused by the El Cheapo wheels, but...

- I didn't have to worry about it for a couple of years because the car wasn't in my possession for that period (long story,) but the vibration really became an issue last year when I put the OEM wheels back on, after I finally found V-rated tires in the stock size on the local market (Bridgestone Turanza AR10).

- That had me looking elsewhere...

- When I first noticed it three years ago, I had the two rear differential mounts replaced (but not the third one at the top front of the diff.) Not much help, this.

- Much later (starting earlier this year,) I replaced a cracked flex disk at the transmission end. No change.

- I took out the prop shaft and had it checked at a specialist shop for the first time, which gave it a "pass" and said it's in "excellent shape."

- Then I replaced the centering bushings at both ends of the prop shaft, along with new front wheel bearings, which improved things by about 80%, but I still got vibes. So far, so good :thumbsup:

- I also replaced all pulleys on the engine: tensioner (twice; first one failed,) main fan pulley (also twice; first one almost failed on a 1,000-mile trip to Amman, Jordan,) and idler pulley. In the course of all that, we found that the crankshaft pulley had been loose, so we tightened that. All of this did improve things, but not much.

- Then I replaced the center carrier, which had its rubber compressed downwards but still in good shape, with an OE spare part, along with the bearing. Nothing.

- I then took out the prop shaft for a second time and had it checked again by the same shop, about four months later than the first time, and the shop still gave me the same report: your prop shaft is fine!

- I had the rear bearings replaced three times: the first replacement bearings (Febi) failed after barely three weeks, one of the second replacements (Lemforder, IIRC) failed again a little later, so my mechanic in Riyadh "ordered" me to go get used complete rear wheel bubs from the junkyard, with which I duly complied. Good call there, but it still didn't resolve the original problem.

- After barely two months, the front wheel bearings (the new Febis I mentioned earlier) failed again, so in went new new ones, also Febis, but Made in Germany (as opposed to the Chinese ones earlier.)

- So, seeing as I did that I was quickly running out of options, I asked my old mechanics in Jeddah to have a go at it. I was a little surprised when one of them told me to go get a new transmission mount, but I went along for both curiosity and the desperation that was starting to creep in. I was surprised again when I compared my seemingly good old mount with the new one, and found that the old one had compressed by about 7mm. So in went the new one, which, again, improved things even more. The transmission now sits higher, which helps there being less of an angle between its axis and that of the prop shaft. Again, so far, so good :thumbsup:

- But albeit much better, the vibration is still there. So I went ahead and replaced the perfectly fine diff-end flex disk just for good measure, but that didn't help at all - a total waste of money.

- Desperation finally having set in, I flushed even more money down the drain: yesterday I bought a set of brand new wheels, had them mounted and balanced, with the new set of tires I bought three weeks ago. No help there.

- Finally, after taking the car for a test drive yesterday evening, I went back to the shop that mounted the wheels and tires had the car up on a hoist. I took off the heat shield and had a look as the prop shaft's center carrier. Noticing as I did that it wasn't "sitting" correctly (it seemed to be mounted at a slight angle relative to the shaft,) I loosened the two bolts and pried it around with a large screwdriver to have it sit as the flexibility of its rubber allowed it to, and then tightened the bolts in that position. I took it for another test drive and found that that helped a great deal! But the vibration is still there, albeit considerably less severe, and only gets annoying at higher speeds (about 170-180 km/h).

PS I scoured the local market for a used prop shaft, but couldn't find any (at least not in Riyadh,) and I was told not to bother searching, because I won't find one for my car; mine had the 14mm bolts, not the much more common 12mm variety. The local dealer asked for upwards of 5,000 riyals for a month-long preorder on a replacement, but frankly, the whole car isn't worth much more than that in the local market, so... :dunno:

So, for now, two questions:

1. How should the center carrier be adjusted? Is there an "optimal position" for it?

2. What purpose does the big nut in the middle of the prop shaft do, exactly? I remember from my W123 days that it had to be loosened in order to take the prop shaft out of the car, but I never needed to mess with it when mounting/unmounting the prop shaft on my 124. Does it need to be tightened/loosened or anything like that? Can it play any role whatsoever in this whole vibration issue?
 

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The driveshaft is a 2 piece unit that is balanced at the factory. IF the driveshaft gets disassembled (example: to replace center support bearing) then it must be marked prior to disassembly and put together in the same way/position to avoid vibration issues.

Make sure the driveshaft end alignment tabs (at the center support bearing) are facing each other perfectly.

See link
PeachPartsWiki: Differential Replacement
 

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Discussion Starter #3 (Edited)
Make sure the driveshaft end alignment tabs (at the center support bearing) are facing each other perfectly.
Yup, already made sure that the "-" in the fore half is perfectly in line with the "=" on the aft half. No issue here.

By the way, I forgot to mention in my OP that I even tried the "jubilee clip approach" just for fun (fun? Really? :D) on a road trip to Jeddah the other week - you know; the whole stop-adjust-stop-adjust affair. That trip took 12 hours! :)
 

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And are you sure that this driveshaft is still the same 2 piece driveshaft that came with your particular from the factory???

If at any point, either end of the driveshaft was replaced you will be chasing vibration issues even if everything looks like its aligned properly.

In other words, if driveshaft replacement is necessary then replace the whole (2 piece) driveshaft not just one piece.

I think you are going to have to consider replacing the whole driveshaft, along with the center support bearing, flex discs and sleeves.
 

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Discussion Starter #5
And are you sure that this driveshaft is still the same 2 piece driveshaft that came with your particular from the factory???
Well, there is no way for me to know if either or both pieces had been replaced prior to me buying the car, or whether I still do have the factory driveshaft in the car, but I would say it's rather unlikely that the driveshaft had been replaced during the prior history of the car, considering that the car only had about 73,000 kms on the clock when I bought it four years ago.
 

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It's rare, but vibration can also be caused by bad axle CV joints. Only seen it happen once on one of my former W116s, but it had LOTS of kms on it (almost 2 million).

In my case, I also went through driveshaft replacement (did nothing) as well as diff replacement (did nothing).

When the driver side axle was replaced, all noise and vibration disappeared. You might want to check your axles.
 

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Have you replaced the tie rod assemblies, center drag link, steering dampener and idler arm bushing?
 

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Discussion Starter #8
Have you replaced the tie rod assemblies, center drag link, steering dampener and idler arm bushing?
Yes, yes, yes, and no. In fact I've had all of these rechecked this Thursday, and I was a little doubtful of the idler arm's condition. I just drove 600 miles to Jeddah yesterday (which is much, much more tiring and uncomfortable than a cross-country road trip in a Mercedes should be :crybaby2:) and I'm going to take a second look this morning after I see if I can hunt down a good used driveshaft in Jeddah's junkyards. I'll report back if and when I get to replace the driveshaft.

On a related note, see the thread I started a while ago titled "Too much caster. Why?" Would that somehow possibly play a role in my situation?
 

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Seems you've replaced most of the wearable rubber components but what about motor mounts?
 

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Hmm. Brake discs? I can feel your pain - I'm chasing down a similar issue right now..... :-/ And that's with a balanced prop shaft & serviced U-joint. To which I would point next.

So far I aligned the center bearing like this: tightend the bolts slightly, drove the car for a short distance (slow) and tightend the bolts down. This seems to work. I can't find any hints for this in the Servie Manual...
 

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Discussion Starter #12
I replaced all four brake disks last year; no change.

Update: we just replaced the driveshaft with a good used one this afternoon (actually, we mixed and matched two halves together which we knew to be good - read on)... guess what? No change - not even the slightest improvement! Same vibration, with the same intensity at the same high speeds. So now I'm confident that my original driveshaft isn't the culprit...

... so, the mechanic and I were talking, and he asked me if I had researched this on the net, and told him that all the discussions we had almost always focused on the usual suspects - wheels, tires, driveshaft... etc. Then I casually told him that I saw a discussion about this:





This is a W124-specific vibration damper that mounts on the back of the rear subframe. The MB part number stamped on it is 124 350 02 72; a quick Google search hardly yielded any results. It's held in place right behind the differential mounts. He, who has a huge warehouse of Benz parts behind his shop, said he might have one lying around, so after some poking around the shelves we indeed found it lying in some dark corner. We're going to install it tomorrow morning and see what happens :dunno::bowdown:
 

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Thumbs pressed! :) Another thing worth a try would be to put a feeler gauge on the front hubs and check them for any run-out... And/or give them a skim on a lathe. Some tyre places also have machines to balance the wheels on the car!

In case I overread it; has the prop shaft been balanced? What about the U-joint? we had the case that this as the culprit :)

------

Looks like I found my issue; I replaced tie rods, wheel bearings and brake discs today - my 110km/h vibration seems to have gone. Autobahn test tomorrow. But looks promising!
 

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Discussion Starter #14 (Edited)
Another thing worth a try would be to put a feeler gauge on the front hubs and check them for any run-out...
I've been thinking about having them checked for trueness for a while. I might do that next.

Some tyre places also have machines to balance the wheels on the car!
Tried that; didn't work. When I said I tried everything, I do mean everything (that I could think of, that is :surrender::D )

In case I overread it; has the prop shaft been balanced? What about the U-joint? we had the case that this as the culprit :)
I had the prop shaft checked twice by a specialist shop on an electronic machine, and both times it turned out to be just fine, and so is the U-joint. In fact, here's an interesting tidbit: the mechanic showed me something yesterday! He suspected that the U-joint might be at fault; they tend to get sticky with time. He got another prop shaft with a sticky joint, and then struck it with a lightweight hammer a couple of times on each of the four stubs. That was enough to loosen it up into a smooth runner. But even that did nothing to solve my problem, either.
 

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... but YOURS did not originally have a sticky joint?

A cautionary tale....

I once had an RX7 acquired from a friend... and during repairs, realized that one of the u-joints was failing... so I chose to replace them both.
Come to find out that the front joint was frozen in a not-quite-straight position. Replaced it and continued on with the rear.
Thought things were hunky-dorey, until...

I began to drive to my brother's place in CA (from Vegas) I suddenly started getting SERIOUS vibration just before the rear half/output section of the transmission EXPLODED, allowing the driveshaft to bounce around the tunnel/road/wherever until I could get to a stop.

Apparently the frozen joint caused the output shaft to bend in kind, balancing out the bend in the joint. Once the joint was operable, the entire area lost its 'compensated balance' and vibrated the transmission into little tiny bits. :eek:

The replacement didn't go well either and I ended up sacrificing it to the salvage gods...
:(

... not exactly sanguine, but possibly relevant. Possibly the yoke on the transmission isn't quite true?
:D
 

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Discussion Starter #16
... but YOURS did not originally have a sticky joint?

Possibly the yoke on the transmission isn't quite true?
:D
1. Yes, it did, but the hammer method I just mentioned took care of that quite nicely on the "test" driveshaft we just installed, but it wasn't enough to solve the problem.

2. There is no "yoke" on the transmission. The driveshaft has only one U-joint just aft of the center carrier, where the fore and aft halves are joined. On the transmission side is the three-legged flange to which the flex disk is bolted. We already had that checked for trueness by running the transmission at high speed with the driveshaft off. No problems there.
 

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1. Yes, it did, but the hammer method I just mentioned took care of that quite nicely on the "test" driveshaft we just installed, but it wasn't enough to solve the problem.

2. There is no "yoke" on the transmission. The driveshaft has only one U-joint just aft of the center carrier, where the fore and aft halves are joined. On the transmission side is the three-legged flange to which the flex disk is bolted. We already had that checked for trueness by running the transmission at high speed with the driveshaft off. No problems there.

That's actually what I was referring to... but I see you checked it.

:thumbsup:
 

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Discussion Starter #19
Right. Here we go:



Better, but not quite. Here's what I figured out:

I had replaced the idler arm and both tie rod assemblies on Monday with new Lemforder units and gave the car a full alignment on Tuesday. I headed out on a 900-mile drive from Jeddah to Amman, Jordan early on Wednesday morning, perfect for a lengthy test drive. As it turned out, the vibration I had been feeling through the floor pan all along is now the same one I'm feeling through the steering wheel! Apparently, the new parts rendered it more intense and vivid - enough to be felt clearly through the steering wheel. So now I'm thinking I might have a warped front hub that's been the cause of all these shenanigans all along!

I'm taking it to my cousin's shop in Amman today or next Saturday for a thorough look-over, because I think that the front bearings that I had replaced twice over the past three months have gone bad again - all the more reason to validate the warped hub theory. I'll report back ASAP.
 
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