How to replace the center bearing, support, and flex discs W126 3.0

[jay3000]

Tools you'll need: metric wrenches 13, 15, 17mm.. Metric sockets 13,15,17mm., 8mm hex key ,long 3/8 ratchet, several extensions, hammer, soft chisel, and soft brass punch, or similar..Prybars, and big screwdrivers come in handy too..Also needed would be a floor jack, jack stands, and ramps.. Oh, a bench vise is quite handy too..

With the front on ramps, and the rear firmly supported bt jackstands, start by removing the 4 rubber exhaust hangers in the rear, and let the exhaust hang down..I used a floor jack to take the tension off of the hangers, and just slipped them off with a small screwdriver..

Unscrew the heat shield, and wiggle it out of the drivers side.. It will come out.. You may have to pull down on the exhaust a little..
All fasteners ar 13mm.. There are two not so obvious nuts on the rear ot the shield..

Grab a 17mm wrench, and a long ratchet with a 3"extension, and an 8mm hex key on it..Remove the three fasteners holding the front flex disk to the tranny..Leave the flex disk attached to the driveshaft.. Do the same in the rear.. Leave the disk attached to the driveshaft. (different tools may have been needed for the rear).. Remember, you can rotate the driveshaft to get to the bolts.. That's why the rear is not on the ramps...

Pry the flex disk away from the tranny, and differential..
Remove the two bolts holding the center support (13mm) while supporting the weigh with one hand..The DS will rest nicely right on top of the exhaust..Feed the whole driveshaft right out the rear..

Holler at wife to fetch another beer

On the workbench.. There are marks on each section of the DS that indicate that the two sections must be reassembled with the marks lining back up . They look something like this(<-).. If not, mark it so the two pieces stay in the same relation to one another.. Seperate the two pieces at the splines. On the rear section, replace the old disk with a new one.. I'm sure there are torque specs for this somewhere. Real tight works though..

On the front section.. Put it in the vise being careful not to damage the shaft.. Spray the bearing liberally with penetrating oil. To remove the center bearing, first work the metal dust shield off with a small screwdriver by prying it off slowly working your way around the shaft.. (looks like a bent washer) The support and bearing are still attached.. Take a soft chisel, or punch, and hammer the bearing off of the shaft working around in a circular motion slowly so that it comes off evenly (it's not on the shaft that tightly)..Leave the rear dust shield on.

Tap the new bearing on SLOWLY until it reaches the old dust shield..Now tap the other dust shield back on.. (neiher are particularly tight) Put a little lube on the new bearing support, and tap it over the new bearing untill it will go no further.. Not much force is required..

Replace the front flex disk with the German writing TOWARD the driveshaft.. It clearly says in German ( this side to driveshaft)

Wipe all of the old grease from the splines on the DS.. Put some nice new grease on, and slide it back together lining the marks back up, and being careful not to damage the rubber dust shield..
Also, put some grease in the bushings ( holes ) In the ends of both shafts where they center themselves..

Holler at wife again

It's now time for reassemby in the reverse order..

It's possible I missed a step here, but I sure can't think of what it was if I did..

No band-aids were required..

I'll try to answer any questions, but I'm certainly not an expert..

Jay..

[HarryM]

Was there a center U-joint, and if so, is replacing it a DIY job?

Thanks

[xp190]

Great Post, I will be doing something similar for my 190E soon.

xp

[RKreutzer]

Hi there,
according to the Mercedes CD, the torque numbers for my 1987 420 (and prob. all the other W126) are:
exhaust shield: 25 NM
engine carrier to frame floor:45 NM
shaft to trans./rear axle:M10=45NM, M12=65NM
Interm. bearing to frame floor:25NM
drive shaft gland nut (not used here):30-40NM
Hope it will help the next diyer.
Regards
Reinhard Kreutzer

[jay3000]

Originally posted by HarryM
Was there a center U-joint, and if so, is replacing it a DIY job?

Thanks

Yes..There is a U joint, but replacing it is NOT a DIY job.. I read somewhere that the best bet is to buy a remanufactured driveshaft ($200).. Mine had an indexed spot in it where you could tell it was worn some, kind of a notched spot, but it moved pretty smoothly otherwise, and was tight.. It seems to work fine..

[vitop]

The U joint can be replaced - not very hard on the non-crimped types. The real problem is that a change of the U joints should be follwed by a re-balancing of the driveshaft. So just have the driveshaft place do both.