Bad Flex Disc - Page 4 - PeachParts Mercedes-Benz Forum

Matt L · #46 03-28-2007, 12:21 AM

I just changed mine.

I read that you have to just make them tight because you can't get a torque wrench in there. That's a severe understatement for a 210. Getting them out was no problem using the air impact wrench, but putting them back in was a real pain, especially in the front. I could hardly get a wrench to stay on the nuts when tightening. I think they're tight enough.

Changing them both took about an hour, plus another two hours to torque the front six bolts. It would have been a lot easier had I removed the transmission mount, but I didn't want to loosen the exhaust. If there's a next time, I will.

If I get a chance, I'll post pictures of the old disks. They're not as bad as any posted here, but I don't know if they've ever been changed.

Matt L · #47 03-28-2007, 12:23 AM

Quote:

Originally Posted by bgkast

It does not look like the rear disk can catastrophically fail. The drive shaft has a hole that engages a pin on the rear differential. If the disk were to fail the shaft would spin, but not flail about causing damage. The front disc is a different matter though...

There's a similar pin on the front disk of mine. But if there is a side load caused by a failed disk, this may also fail. I don't know.
---
After writing this, I thought of something. The center bearing would keep the rear part of the driveshaft from migrating forward, but it will not prevent the front part from migrating rearward on the spline. That pin is no reassurance on the front.

tobybul · #48 03-28-2007, 10:36 AM

Checked the shaft this morning and found the center shaft support to be bad and loose

. The rubber part had tears. Shoulda taken a picture. I'll do that tonight and post it.

The flex discs appeared to be in good shape.

Does this mean I have to drop the entire shaft to change this support? Or does it come apart at the u-joint? Help!!!

DeliveryValve · #49 03-28-2007, 10:59 AM

Quote:

Originally Posted by tobybul

Checked the shaft this morning and found the center shaft support to be bad and loose

. The rubber part had tears. Shoulda taken a picture. I'll do that tonight and post it.

The flex discs appeared to be in good shape.

Does this mean I have to drop the entire shaft to change this support? Or does it come apart at the u-joint? Help!!!

You will have to take the whole shaft out in order to replace the center support bearing. It is not too bad of a job.

Alberta Luthier · #50 03-28-2007, 11:10 AM

Quote:

Originally Posted by Matt L

I just changed mine.

I read that you have to just make them tight because you can't get a torque wrench in there. That's a severe understatement for a 210. Getting them out was no problem using the air impact wrench, but putting them back in was a real pain, especially in the front. I could hardly get a wrench to stay on the nuts when tightening. I think they're tight enough.

Changing them both took about an hour, plus another two hours to torque the front six bolts. It would have been a lot easier had I removed the transmission mount, but I didn't want to loosen the exhaust. If there's a next time, I will.

If I get a chance, I'll post pictures of the old disks. They're not as bad as any posted here, but I don't know if they've ever been changed.

On my 123 it was perhaps even more difficult to get at. The nuts are quite shallow and the wrench very nearly stripped the nut until I ground the side of a box end wrench flat to get past the inside bevel of the wrench. -And this with the trans mount and exhaust pipe removed.

Alberta Luthier · #51 03-28-2007, 11:17 AM

Quote:

Originally Posted by Matt L

There's a similar pin on the front disk of mine. But if there is a side load caused by a failed disk, this may also fail. I don't know.
---
After writing this, I thought of something. The center bearing would keep the rear part of the driveshaft from migrating forward, but it will not prevent the front part from migrating rearward on the spline. That pin is no reassurance on the front.

The center bearing will only hold the shaft from coming forward and disengaging the center pin till the rubber mount fails. I don't think that would be very long. The large nut on the shaft should stop the shaft from migrating rearwards, but again I'll bet it couldn't for very long especially if, for example the front disk let go at highway speed, and the differential turning the driveshaft with only the center bearing and it's rubber mount holding the rotating, thrashing front end of the shaft etc..

tobybul · #52 03-28-2007, 11:20 AM

Quote:

Originally Posted by rmarzan

You will have to take the whole shaft out in order to replace the center support bearing. It is not too bad of a job.

Thanks, Kababayan....

Just confirming, I guess this means unbolting the flex disc? Both front and back? Now am wondering whether to just change them too since I got them off.....

Alberta Luthier · #53 03-28-2007, 11:21 AM

Quote:

Originally Posted by rmarzan

You will have to take the whole shaft out in order to replace the center support bearing. It is not too bad of a job.

Then having taken apart both disks(among other things) to drop the shaft, you have to decide if, as good as they look, do they look good enough that you want to reuse them.

tobybul · #54 03-28-2007, 11:26 AM

Quote:

Originally Posted by Alberta Luthier

Then having taken apart both disks(among other things) to drop the shaft, you have to decide if, as good as they look, do they look good enough that you want to reuse them.

Am gonna check whatever service records I have from the PO if the FD's had been replaced and when. If no records, may have to replace. I am guessing that the center support is the orig on the car.... but the FDs may not be considering the the mileage - 242k - seems like it would be pretty beat up by now but they actually look pretty good. As you said, I'll have to decide after I take it apart. another factor is how well lock nuts hold up when removed and reinstalled.

Alberta Luthier · #55 03-28-2007, 12:06 PM

Quote:

Originally Posted by tobybul

Am gonna check whatever service records I have from the PO if the FD's had been replaced and when. If no records, may have to replace. I am guessing that the center support is the orig on the car.... but the FDs may not be considering the the mileage - 242k - seems like it would be pretty beat up by now but they actually look pretty good. As you said, I'll have to decide after I take it apart. another factor is how well lock nuts hold up when removed and reinstalled.

That is a lot of miles if original. I forget what the size was, but I did find that grinding the face of the box end wrench flat made a BIG difference for me.

tobybul · #56 03-28-2007, 12:15 PM

Quote:

Originally Posted by Alberta Luthier

That is a lot of miles if original. I forget what the size was, but I did find that grinding the face of the box end wrench flat made a BIG difference for me.

I believe I read that in one of the posts, too.

Matt L · #57 03-28-2007, 01:22 PM

I almost got out the grinder. I think I got the fronts tight enough, but the wrench is so touchy that it's hard to be sure. I think I will grind one down and try again, just to be absolutely sure.

bgkast · #58 03-28-2007, 03:14 PM

Quote:

Originally Posted by tobybul

Am gonna check whatever service records I have from the PO if the FD's had been replaced and when. If no records, may have to replace. I am guessing that the center support is the orig on the car.... but the FDs may not be considering the the mileage - 242k - seems like it would be pretty beat up by now but they actually look pretty good. As you said, I'll have to decide after I take it apart. another factor is how well lock nuts hold up when removed and reinstalled.

For what it is worth the dealer was able to get me a flex disk for less that I could find it for online.

Matt L · #59 03-31-2007, 10:26 AM

Grinding on the wrench made enough difference. I was able to ensure that all twelve nuts were tight. It's a 17mm.

I am not sure that my disks were original, but it wouldn't surprise me. 10 years, 201K miles.

wawago · #60 04-03-2007, 03:56 PM

Hi, I have about a week of free time. I am thinking about changing my differential fluid, front and rear flex discs, front and rear diff mounts, and lastly transmission mount on my 88 300ce I am wondering is there anything else I should replace for additional minimal work and prevent future problem while tackling the above tasks? For replacing the two rear differential mounts (bushings) I know it would be easier with a special MB tool. But how can one remove and replace the mount without the tool? Thanks. James.

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