W126 Driveshaft rubbing
 

Hello all,

I have a 1991 300SE and today I changed my differential fluid, very easy if you have the correct tools lol. While I was under there poking around I notices the driveshaft is rubbing the heat shield for the muffler. The shield doesn't look adjustable so I figure something must be out of whack. The front and rear diff mount look pretty old, the transmission mount looks newer as far as I can tell.

The previous owner put what looks to be a 1 inch or so spring spacer in the back. He said he didn't like the way the back end sagged. Could that also be an issue?

Picture time!

This is where the drive shaft is rubbing
https://scontent-iad3-1.xx.fbcdn.net...be&oe=5A992D12
Another angle
https://scontent-iad3-1.xx.fbcdn.net...ef&oe=5AC6CC37

Trans mount
https://scontent-iad3-1.xx.fbcdn.net...c9&oe=5ACCF5D1

Differential mount, looks pretty sad.
https://scontent-iad3-1.xx.fbcdn.net...87&oe=5AD3AC82

Differential front mount, not sure if there are more that's all I saw
https://scontent-iad3-1.xx.fbcdn.net...01&oe=5A91754D

The spring spacer
https://scontent-iad3-1.xx.fbcdn.net...22&oe=5A8CFE02

I hope this is just an optical illusion, but in the image it appears that the transmission housing where it mounts to the transmission mount has a major crack.

Also it´s difficult to decipher the rear spring. if the images were a little smaller it might be easier to interpret them.

Never mind, I just figured out that those illusions are shadows.

The differential mount doesn´t appear to be causing the problem, although old, but is it missing rubber on the top part? The transmission mount looks good

I shrunk down the pictures of the springs.
Left and right are posted below. I'm really leaning towards the rear diff mount. I looked at a new one and there is a sizeable gap between the inside piece and the bottom, mine does not have that gap so I guess it's collapsed from age.

https://scontent-iad3-1.xx.fbcdn.net...b9&oe=5AD7BCE4

https://scontent-iad3-1.xx.fbcdn.net...cd&oe=5A938FC0

The Diff mount can collapse fully and it won't do anything to the driveshaft. I'd pull the driveshaft cover off and check the carrier bearing. If it's fallen apart or come loose, it could let the driveshaft drop enough to drag like that

I have no vibration or weird noises though. I thought the carrier bearing being bad would cause symptoms you could hear and feel?

The diff mount has a stop in it to prevent the diff dropping too far. When it drops down to its max limit, it just rubs on the mount holder. The one in my SDL was completely collapsed and the driveshaft still cleared the driveshaft tunnel cover.

Guess I need to drop that cover then. Will it clear the exhaust when I unbolt it? What am I looking for once I get in there?

Not sure about the gas engines, it cleared on the diesel with room to spare, but there's no cat or anything on the diesel.

You're looking specifically at the carrier bearing mount. See if it is worn out or if it's come loose. Sometimes the rubber in the center deteriorates and the whole driveshaft will drop down a bit.

I'll see if I can get to it tomorrow to check it out. If the mount is bad, can it be replaced without removing the center bearing from the driveshaft? Or since the driveshaft would have to be pulled anyway should the bearing just be replaced too? At the same time I'd probably do front and rear flex discs.

Popped the heat shield off this morning. The carrier mount is definitely bad lol, I can see through it.

https://scontent-iad3-1.xx.fbcdn.net...a8&oe=5A9D6169

Well there's your problem! Replace the bearing while you're at it. If the flex discs look old and tired or if they're cracking, it's a perfect time to do it while you're in there.

The flex discs do look a bit tired so I'll replace them along with the carrier mount and bearing.
I'll do mercedes brand for the flex discs. Is there a brand preference for the carrier mount?

I agree. Definitely MBZ flex discs and if you don´t buy the kit, at least use new castellated nuts since the old nuts can lose their gripping ability after being removed. And since the driveshaft will be off, check to make sure there is no play in the u-joints. If so, you will need to have a driveline shop replace them after the new center bearing / support has been replaced. It´s not too expensive by comparison.

When you separate the front and rear halves of the DS, mark each half clearly to line them up when putting them back together - if you don´t, the DS will vibrate.

Both center carrier bearing and support are inexpensive - MBZ or German aftermarket, but stay away from URO brand.