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Old 02-12-2018, 06:44 PM
Shern's Avatar
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Flex disk/center bearing techniques

Hey all - Had 240D (manual) up on a lift the other day and noticed my drive shaft carrier was pretty destroyed. I'm assuming the bearing isn't too hot either. Couple questions...

1.) The job seems relatively easy but I have no access to a car lift. Has anyone done these repairs via an alternative method? Jack stands, curb, etc?

2.) As a preemptive measure I plan on replacing the flex disk closest to the differential. Most references I've found were to automatic transmissions on 300Ds. Forgive my ignorance, but I'm assuming there are also two on manual transmission 240Ds?

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Old 02-12-2018, 06:59 PM
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You'll have 2 flex discs. One at the transmission tailpiece and the other at the differential. If one is in sad shape, the other isn't far behind. Replace them both. I did mine on the SDL with the car up on Rhino-Tuff Ramps. Check the driveshaft while you have it out, if the U-joint is notchy or rough, it might be time to source a rebuilt one with a fresh set of bearings.
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Old 02-12-2018, 07:05 PM
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Quote:
Originally Posted by Diseasel300 View Post
You'll have 2 flex discs. One at the transmission tailpiece and the other at the differential. If one is in sad shape, the other isn't far behind. Replace them both. I did mine on the SDL with the car up on Rhino-Tuff Ramps. Check the driveshaft while you have it out, if the U-joint is notchy or rough, it might be time to source a rebuilt one with a fresh set of bearings.
Just had a look at those ramps on amazon... not bad. Did you use them on the front wheels or the rear wheels? Have read that one must keep the transmission in neutral when doing this job.
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Old 02-12-2018, 07:06 PM
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I've done this job with the car on jack stands. You should have flex disks at the transmission output and differential input even on a manual, the driveshaft length is whats different. On the automatic I had to jack the trans up and take the transmission mount off to change the disk. For the driveshaft if the center bearing overheated too much you'll need a torch and a good 3 jaw puller to pull it off, that is the hardest part.
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Old 02-12-2018, 07:49 PM
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my process for doing driveshaft work has been

four 4 ton jack stands
one 3 ton floor jack

jack up the front underneath the front cross member
put jack stands underneath rockers on both side
jack up rear underneath rear subframe mount and put jack stand underneath rear trailing arm near wheel, repeat on other side

lifted and supported on four corners one an easily access the driveshaft front and rear.

You'll probably want to keep the transmission in neutral so you can rotate the drive shaft to reach all the fasteners on the flexdisk. use the park brake to hold 'er steady while you're torquing off the fasteners.
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Old 02-12-2018, 07:51 PM
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Quote:
Originally Posted by Shern View Post
Just had a look at those ramps on amazon... not bad. Did you use them on the front wheels or the rear wheels? Have read that one must keep the transmission in neutral when doing this job.
I put mine behind the rear wheels and backed up the ramps. Having the tranny in neutral or not will not really matter unless you have the wheels off the ground. You won't be able to rotate the driveshaft unless the wheels can turn.

Setting the center nut in the driveshaft is somewhat critical. You want to have the car on the ground and in neutral so you can rock it back and forth with the nut loose, then squeeze up under there and snug it up. If you aren't too horizontally challenged, it can be done, if you are horizontally challenged, find a curb or something to roll it up onto so you can get under the car. You want all 4 wheels supporting the vehicle weight when you do the final snugging or you can get a vibration issue.

Speaking of driveshaft, make sure you mark the alignment BEFORE you take it apart!
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Old 02-12-2018, 07:57 PM
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Quote:
Originally Posted by Diseasel300 View Post

Speaking of driveshaft, make sure you mark the alignment BEFORE you take it apart!
And for good measure mark the ends of the drive shaft in relation to the flanges they bolt to on the tranny and diff. That way it all goes back exactly the same way.
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Old 02-12-2018, 08:00 PM
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Quote:
Originally Posted by Diseasel300 View Post
I put mine behind the rear wheels and backed up the ramps. Having the tranny in neutral or not will not really matter unless you have the wheels off the ground. You won't be able to rotate the driveshaft unless the wheels can turn.

Setting the center nut in the driveshaft is somewhat critical. You want to have the car on the ground and in neutral so you can rock it back and forth with the nut loose, then squeeze up under there and snug it up. If you aren't too horizontally challenged, it can be done, if you are horizontally challenged, find a curb or something to roll it up onto so you can get under the car. You want all 4 wheels supporting the vehicle weight when you do the final snugging or you can get a vibration issue.

Speaking of driveshaft, make sure you mark the alignment BEFORE you take it apart!

"Setting the center nut" is a step I am just not clear on... couldn't find any references to a center nut in any if the DIY articles. Also, I'm quite a slim guy and I can't even see the drive shaft or any part of it with the car on the ground.
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Old 02-12-2018, 08:05 PM
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Quote:
Originally Posted by Shern View Post
"Setting the center nut" is a step I am just not clear on... couldn't find any references to a center nut in any if the DIY articles. Also, I'm quite a slim guy and I can't even see the drive shaft or any part of it with the car on the ground.
The driveshaft is a 2-piece affair. There's a nut that holds the bearing on and clamps the 2 pieces together at the slip joint. I haven't been under a 123, but the 126 has a cover over the driveshaft, so you can't see it when looking under the car. When I did mine, I rolled it off the ramps, back and forth a couple times, then backed it up the ramp, put it in neutral and rocked it back and forth a couple times before climbing under and snugging the nut. The wheels never left the ground, so I considered it "good enough" for what I had to work with.
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Old 02-12-2018, 11:45 PM
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Thanks for advice - I bought some ramps on amazon this afternoon.

Any one else performed this repair sans lifts/jack stands?
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  #11  
Old 02-13-2018, 01:28 AM
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In post #32 is a description on how to free up a sticky/notchy U-joint.
W123 Propeller shaft vibration tears up rubber mounts, replaced nearly everything

Long before I came across that thread I had replaced the U-joint on my own drive shaft. There is 2 threads on how to do that. The U-joint is still available.
U-Joint 2005 not my thread
Can you replace the universal joints?????
My U-joint Repair thread 2011
Drive Shaft U-Joint Is Staked/Crimped In Place, Now What To Do?
My Benz World post with all of the U-joint sources.
http://www.benzworld.org/forums/w123-e-ce-d-cd-td/1581728-another-u-joint-driveshaft-thread.html#post4677977

Also besides the Flex Discs in the center of each end of the drive shaft is a centering bearing. It is a tube with a seal and a bearing inside. If replacing them is not need they do need to be lubed inside.

Tightening Drive Shaft Collar Nut (coupling nut) 2011 post #40
How to replace the driveshaft support (carrier) bearing - A step by step guide - Page 3 - PeachParts Mercedes ShopForum
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Old 02-13-2018, 07:19 AM
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I used 6 ton jack stands when I replaced my front flex disc. I started off on ramps, but I couldn't get all the bolts out... needed to turn the shaft to get to the last two. With the rear end on jack stands, I could turn the shaft by hand.

Be absolutely sure you mark the shaft so it goes back on in the same orientation to the flanges.
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  #13  
Old 02-13-2018, 12:25 PM
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Super helpful, thank you!

Quote:
Originally Posted by Diesel911 View Post
In post #32 is a description on how to free up a sticky/notchy U-joint.
W123 Propeller shaft vibration tears up rubber mounts, replaced nearly everything

Long before I came across that thread I had replaced the U-joint on my own drive shaft. There is 2 threads on how to do that. The U-joint is still available.
U-Joint 2005 not my thread
Can you replace the universal joints????? - PeachParts Mercedes ShopForum
My U-joint Repair thread 2011
Drive Shaft U-Joint Is Staked/Crimped In Place, Now What To Do? - PeachParts Mercedes ShopForum
My Benz World post with all of the U-joint sources.
Another U-Joint / Driveshaft Thread - Mercedes-Benz Forum

Also besides the Flex Discs in the center of each end of the drive shaft is a centering bearing. It is a tube with a seal and a bearing inside. If replacing them is not need they do need to be lubed inside.

Tightening Drive Shaft Collar Nut (coupling nut) 2011 post #40
How to replace the driveshaft support (carrier) bearing - A step by step guide - Page 3 - PeachParts Mercedes ShopForum
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  #14  
Old 02-13-2018, 12:27 PM
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Were you using ramps on the front or back wheels?

I'm also going to replace the front flex disc and want to make sure I have enough room.

Quote:
Originally Posted by Bengoshi2000 View Post
I used 6 ton jack stands when I replaced my front flex disc. I started off on ramps, but I couldn't get all the bolts out... needed to turn the shaft to get to the last two. With the rear end on jack stands, I could turn the shaft by hand.

Be absolutely sure you mark the shaft so it goes back on in the same orientation to the flanges.
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  #15  
Old 02-13-2018, 12:49 PM
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When I did this, I didn't bother putting everything back exactly. Just dropped the drive shaft, replaced the discs and center carrier support, and put it all back.

No vibrations or anything! Totally was fine.

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