Flex disk?

[matt7531]

My mechanic says I need a new "flex disk" on my drive shaft, to the tune of $300, on my 84 380SL. Is this something a fairly unskilled do it your selfer can do? And what is a flex disk, anyway?

[kip Foss]

Replacing the flex disk is a 1 hour job.

Jack the back of the car.
Support it on GOOD jack stands on firm ground.
The bolts require either 17 or 19mm wrenchs I can't remember which.
Remove the driveshaft to differential bolts.
Loosen the two bolts that hold the driveshaft carrier bearing. It's on the transmission end of the shaft you are working on. It will allow you to slide the driveshaft forward enough to slide out the flex disk.
Replace the disk.
Reverse the video.

[matt7531]

Thanks kip. So the disk is attached to the differential? Is this a one man job, or will I need help with the drive shaft? Are the SL drive shafts in a tunnel set up like other foreign cars?

[ctaylor738]

WADR, there is more to it. You need to drop the exhaust, and remove the heat shield and the cover/stiffener plate. This requires removing the trans mission mount. There are flex discs at the transmission and differential end. If you are going to do the discs, you might as well do the center bearing as well. It's a dirty, tedious job.

What is a good indication that the Flex disk needs replacing? I have a rumble coming from under the car under acceleration sometimes.

[matt7531]

I don't have any type of noise. Two mechanics at two different shops told me it was shot, and the last one told me I am going to really do a number on my car if I don't get it fixed.

[matt7531]

Originally Posted by ctaylor738

WADR, there is more to it. You need to drop the exhaust, and remove the heat shield and the cover/stiffener plate. This requires removing the trans mission mount. There are flex discs at the transmission and differential end. If you are going to do the discs, you might as well do the center bearing as well. It's a dirty, tedious job.

Yikes! So you think I should let a shop do it for $300, and tell them to do the center bearing at the same time?

[ctaylor738]

My 280SL had both a bad center bearing and a bad flex disk at the trans end. That front one has a sort of webbing between the trans bolts and the shaft bolts. The webbing allows some "give" when the trans goes into gear, and when accelerating. After a while, the webbing breaks down. and the driveshaft sort of bounces around in the disk.

The rear disk is solid, and is probably OK.

You need to trust your tech on this, but ask him to save the disc for you.

[matt7531]

It's an 84 380SL. The parts list only shows one flex disk. Does the same one fit both ends or does the 380 just have one?

[Kebowers]

On this car there is ONE flex disk mounted between the transmission and the driveshaft. The rear end has a convention universal joint.

[Strife]

Strange...my MB shop manual CD shows front and rear flex disks on an 84 380SL.

[ctaylor738]

The online sites show a front and rear, but they are the same for US (automatic) - my setup was for a 5-speed.

I have never seen a Mercedes that did not have discs at both ends but that doesn't mean there aren't any.

[matt7531]

Ok, I talked to the mechanic. He says it is the one that connects to the transmission. He also disagrees with replacing the center bearing, he checked it and says it is fine. Now, my question is, is the procedure outlined by Kip the way you replace this part, or is kip describing replacing the one that connects to the diff? If I only do the flex disk, is it something a poor college kid with minor experience can do? I can get the disk over the internet for like $83 dollars.

[ctaylor738]

If you just do the front, the only steps to add are:

- support trans with jack
- unbolt trans mount
- remove stiffening plate, which runs under the driveshaft

Then the trick is to loosen the big nut on the driveshaft so that when you undo the nuts on the coupling, you can slide the dhriveshaft back enough to get the coupling out. That is a big-assed nut, like 38 - 42 mm. If you can manage that, then it's basically just nasty, dirty stuff under the car.

If you send me an email, I will send you the chapter off the CD.

[jdhill]

I have the same question as Matt. What does a flex disc do? Is it really necessary? What about a one piece shaft?
Thanks.