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If you're transmission is jerky while shifting, this may be the problem.
I bought some of these, but I inspected mine, and they looked fine. I am told this is pretty hard, because you have to keep everything aligned. This may be a shop job for me, when the time comes.
Not too difficult . If the front especially fails at freeway speed you are in deep shit. Very deep.
You'll need a floor jack and jack stands or large wood blocks to be able to get the car up in the air far enough to work comfortably under it. I was OK raising it about 12" so I had about 22" clear space under it.
On my 1978 240D the differential is fixed, ie attached to, has a fixed relationship with the chassis and transmission drive flange. On some older ones it floats with the movement of the rear axles through bumps etc. With those it is necessary during installation to have the weight of the car on the rear wheels because that affects the driveshaft position and length during the last step of driveshaft installation: tightening the nut on the shaft which freezes the splines connecting the two sections.
1- put vehicle securely up in the air for comfortable and safe working underneath.
2- remove exhaust system from down pipe to tailpipe (4 rubber bands and one clamp)
3- loosen parking brake adjuster bolt, disconnect cables etc to allow easy driveshaft removal
4- unbolt both flex disks from transmission. and differential drive flanges.
5- unbolt carrier bearing bracket
6- loosen the large nut concentric on the driveshaft just ahead of carrier bracket to allow the driveshaft to telescope a bit shorter. They want about 30 ft/lbs of torque in mine, check for specs on your model. Requires a 41mm or 46mm open end wrench if your torque spec is much higher, I was OK with a large channel lock plyers at 30 ft/lbs.
7- Using a punch, or sturdy screwdriver, and hammer tap flex disc at its steel bushings where the bolt goes through to free if from the drive flange.
8- At each drive flange a central steel bushing keeps the shaft perfectly centered on the flange ... those bushingsa are mounted in the drive flange of the differential and transmission. The driveshaft will telescope a bit, the rear section moving forward until it disengages from its centering bushing. Drop rear section some, but support it, then withdraw the front section.
9- if the U joint on the two piece shaft is not newish you'll need a rebuilt shaft complete ... off the shelf, $315 and 2 days later by UPS ... flex disks not included. Mercedes builds these driveshafts such that the U joint isn't easily replaceable. I suspect that is related to making sure its properly balanced to zero out vibration. Replace the carrier bearing and bracket if its rubber suspension is at all questionable. They are included in a rebuilt. If the two sections become separated mark them near the splines before separating them and put the two back together in exactly the same position. Thats necessary to keep it balanced.
10- This is the time to replace the transmission mount if its shaky. The new one I got didn't fit ... a steel bushing mounted in it was too long ... but slid right out of its rubber imbedment and I used the bushing from the original.