joining drive shafts
 

I've read where its reccomended to mark the 2 halfs of a drive shaft when removing from the vehicle so that they are reinstalled in the same relative position later. If I'm using the front half from one shaft and the rear half from another, is there any special directions on how the spline fits together?

I think that's what you call being extra careful. I'm unaware of any good reason for it. But, I would like to hear one if there is.

The drivesghaft is factory balanced. So it is very important to assemble them as they came apart. Mixing a non matched front and back portion of the shafts may or may not cause an issue.

The balance of the new to each other shafts should be balanced on a machine really for best results. Not too hard to pull them again if a vibration is present. Myself I might try balance the front shaft to match the one taken off if I knew the match marking of the original frontshaft. Just duplicate it on the second short shaft and balace it the same as the old one. It would be tricky to do at home though.

When I pulled the driveshaft halves apart on my 240 in 2006 I didn't mark the halves and put it back together without knowing the original orientation. That was 70k miles and 6 years ago, I've never noticed any vibrations. I wouldn't worry about it too much.

Something about that just doesn't sound right. If the shaft is balanced, then it shouldn't make any difference. If the shafts are not balanced, and somehow depend upon their orientation relative to each other to balance... I'm still scratching my head on this one.

The FSM shows that in about 1982 MB got their act together and put alignment marks on the two D shafts - and also say that the alignment marks were not paid attention to in assembly - so please correctly align them in service.

The marks are a triangle on one shaft and a square on the other.

The shafts should be balanced as a pair - a special relationship between the front and the back if you like.

If you take then apart and then refit them incorrectly the special relationship is broken => you could experience prop shaft vibration problems.

Zulfiqar kindly posted the FSM notes which mention both the alignment marks, and the fact that the marks were ignored at assembly time.

In the name of expediency, I have no problem blindly following the FSM advice, that's what I'd do, and what I'd recommend to anyone. But, as a general principle, I try to undertake projects in a mindful and purposeful way. While I understand that it is possible under limited circumstances, to balance shafts in such way. I can't see why anyone would ever think it is a good idea. Most especially an MB engineer. Can you explain why? Are you aware of any consequences for not doing so?

In typing this, I've just realized that like Biodiesel300TD, I have also used mismatched shafts in my TD, and noticed no problem.

Do you mean why they balanced the prop shaft as a whole (two sections together) instead of doing each section individually and then joining the two together (I've learnt recently that this is often called neutrally balanced!)?

Yes, why invite the possibility for error at time of manufacture.

Got any source you can share about neutral balance. I can only find stuff that relates to high RPM racing engines, which doesn't apply to driveshafts.

Phasing U Joints
 

Here's a bit of an explanation:

Driveshafts and U-Joints - Tom Sotomayor

Any two piece shaft should be marked before being taken out so that the two halves go back together in the same relationship, otherwise vibration can be a problem. I just grab a crayon/marker and run a line across the bottom of the shafts where the middle U-joint or splined joint is.
See figure 2 in this page:
http://jeepgarage.free.fr/OWN/drive%20shaft%20alignment.pdf

After a certain year they are marked by bumps on the Casting.

In another thread I speculated that he Prongs on the Yoke had a specife oreintationto the prongs of the Yoke on the opposiet end of the Shaft.
I think that means if there is no marks on the 2 shaft sections there is 3 positions that would work.

I don't have a good pic if the end with the Single Mark on it.

Thanks smiffy, the Tom Sotomayor link cleared it all up for me.

It's not a shaft imbalance problem, it is a limitation of U joints. There's a hint in the name of the u-joint's cousin, the Constant Velocity Joint.

On the W123 we've got those rubber couplings, but they suffer from pretty much the same issue. thanks for the photos.

Does this mean that you believe No one balances Drive Shafts; or that they do nut use the term Neutral Balance where you looked?