W126 Center Driveshaft Bearing Replacement
 

Hey All. I have a 1986 300 SDL and I went crawling around today to replace the flex discs. I pulled the center bearing support to get the play I needed to get the disc off, (location marks were made on both front and rear driveshafts, just in case) and this was where I noticed one of two things I need advice on.

The driveshaft very nearly just fell out of its splined interface with the front half. Some of my research suggests the existence of a ‘slip nut’ that is supposed to prevent this. I did not investigate much further as it was to be hidden by a very worn And disintegrating rubber boot, which I have been unable to find in a parts catalog should I need replacement. If that slip needs to be tightened or inspected I will make sure to do so during re-install.

The center bearing support is destroyed. It gets worse just by looking at it. However everything that I can find for replacement is a stand alone bearing and a support bracket. My bearing and support are one single unit. The outer race of the bearing is molded into the run or support. The part number from my old unit is 124 410 02 80 which pulls some eBay and such listings. Will the two piece kits on Pelican Parts fit or do I need to replace like for like?

Cheers,
T.P. Crockmier

The bearing and support carrier are separate pieces. The support carrier and bearing are typically sold separately, so yes, they're the correct part. The slip nut on the driveshaft will be tightened after you finish reassembling and have the weight of the car on the ground. Put the transmission in neutral and roll it back and forth a bit before tightening. It need be only snug, you don't have to go crazy with it.

Here's a How-To from this site: http://www.peachparts.com/shopforum/diesel-discussion/278920-w126-drive-shaft-carrier-center-bearing-diy.html

While you're under there and have the driveshaft apart, check the U-joint for stiffness or notchiness. It should be smooth and free. A ratchety feeling or stiffness indicates it needs replacement.

Hey thanks so much for the info. I won’t be able to get under the car when it’s on the ground so I’ll have to try and figure out how to get that tightened up as you said.

I have that thread open and have been using it for reference. It’s been a great help so far but I was a bit confused when it was talking about and showing pictures of snap rings, as there is no such retention on my original bearing, it’s just pressed on. And there is a part assembly that gets referenced that isn’t quite relevant to my driveline, which is why I had some questions and came here, but a great resource nonetheless.

The U-joint is indexing. It wants to index to a straight position. I’ll likely have a local driveshaft shop press the new bearing and carrier so I will ask him about getting that overhauled. It’s a daily driver so I only have about a week left of vacation to get it back up to speed.

Typically on these cars when the flex disc needs replacing so does everything else on the drive shaft, including the support, bearing, boot, etc. The joint should not have slid apart like that, it should have been tight with the giant 46mm nut/collar.

T.P.Crockmier, place a ramp or stack of pieces of 2"x6" wood under each wheel so you can crawl under your W126 to tighten the slip nut.

Cool, cool. I’ve got the carrier on the way and it should be here in a couple of days. In the mean time I’ve got some scrap lumber that I can fashion into blocks to put the car on.

Hopefully with everything replaced my driveline will quiet down a bit and I’ll certainly gain some peace of mind.

I use 2 sets of ramps for this. After driving the car onto the front ramps you jack the rear from the differential and slide the second set of ramps under the wheels. Place them with the angled part facing forward, hence, wheel stops in both directions. You may need a another jack to raise each trailing arm slightly to insert the ramps.

Tighten the 46mm nut with the center bearing support close but not tight. You can bounce the car up and down from the rear, which has the same effect as rolling it. Now you can tighten the center bearing support, which should be done last.

I ended up making wheel cribs out of 2x4s. Had to walk the car up on to jack stands and then get a bigger piece of wood to get it up the last few inches. Worked like a charm, and I had a good amount of room under the car.

Tightening torque on the big center nut is only 30-40 NM. It's intended to slip a tiny bit as the car moves around; makes life easier on the flex joints. At that torque it is also possible with a little bit of "oomph" to slide the joint back to remove a flex joint or tranny.

DG

Does anybody know if with the clamping nut loosened, can you slide the shaft into itself such that it basically drops out, or is it still a lot of reefing required to get it to drop out?
Cheers

With the 46mm nut all the way back to loose, the two halves can be moved so much that they can even be separated- so be sure mark both halves before removal. Marking is a good idea even on later driveshafts that have factory markings.

Thanks EZ I'm tackling this one tomorrow I'll be sure to mark that bad boy up good!