I wasn't saying that the rebuilderrepairer was going to install a larger U joint, but that the service which makes you a whole new driveshaft uses a larger U joint, and makes it easily replaceable.

The question in my mind is whether a larger U joint, on a "new" driveshaft, is inherently stronger and more advantageous in any way.

So, I sourced a used driveshaft which has the same color coding marks as the one on my car, and is the same length 77 inches, and according to the use parts dealer is for the 1986 300 SDL.

I thought I would get it, run it by my mechanic before rebuilding to make sure it's the right one.

Parenthetically, if anyone on the forum knows a Mercedes mechanic who is good with these older cars, I know a garage in Los Angeles (not the one I usually use) who is looking to hire such a good mechanic.

I have 3 used ones I can sell if you want. I think you might be making this too complicated though, It's not hard to swap at all, and that one I bought last year that I posted a link to is still working great. If you can jack the car up safely that's about the hardest part of the whole job, it's easy to actually remove the driveshaft and put the new one in. Make sure you change the flex discs too, because breaking one on a W126 probably will damage the car beyond repair.

What's the condition of the driveshafts? Any of them low mileage? The one I sourced near me in has the right color coding on it for my 1986 300 SDL.

Where are you located?

Thanks

My sentiments exactly. The OP is probably still fussing around with finding the best "deal" on a driveshaft and obsessing over rebuild options. The factory driveshaft U-joint fails not because it's weak but because it's old and has a lot of miles. Nothing lasts forever.

My 560SEL needed a driveshaft (nearly seized and VERY notchy U-joint). I called DSI (who's website I linked above) on Monday, got the replacement driveshaft Wednesday, and installed it by myself yesterday afternoon in roughly an hour and a half. It took more time to get the car up on jackstands, gather up my tools, and clean up after the job than it did to actually swap the driveshaft. Old one is back in the box to go back to DSI as a core for rebuild and my car is now vibration and noise-free. No muss, no fuss, no BS, and now a driveshaft with a smooth and quiet U-joint and fresh center support/bearing with a warranty.

I personally will not use a used driveshaft unless the U-joint is PERFECT. The BS-factor is just high enough to make this a job I want to do once and do right and I HATE vibration from the drivetrain.

__________________
Current stable:
1995 E320 149K (Nancy)
1983 500SL 120K (SLoL)

Black Sheep:
1985 524TD 167K (TotalDumpster™)

Gone but not forgotten:
1986 300SDL (RIP)
1991 350SD
1991 560SEL
1990 560SEL
1986 500SEL Euro (Rusted to nothing at 47K!)

I am neither fussing, nor trying to find the best deal, but trying to understand a subject about which I knew nothing prior to three weeks ago. That's it.

This may be old hat and obvious for some, but not for everyone. And I intend to make a good decision.

I happened to overlook what might be a very good resource, Driveshaft Specialists of San Antonio which Diesel 300 posted. They're not answering today, although they' re supposed to be open, so I'll wait till Monday.

What they're describing, rebuilds done to the exact German specifications, sounds just like what I'm looking for.

I have 3 of them, all which need to be balanced and the U-joint replaced. I am located in Vacaville CA.

Thanks.

I think I may go with the solution that Diesel300… the company in San Antonio… came up with. There they use original driveshafts which they procure and rebuild. Looking forward to talking to them on Monday