Driveshaft center nut/splines

[Usaguy]

are the splines supposed to move in and out on the driveshaft with the nut tightened to factory 30-40nm to allow for expansion?

anyone with a driveshaft laying around up for an experiment?

[Diesel911]

Originally Posted by christuna

are the splines supposed to move in and out on the driveshaft with the nut tightened to factory 30-40nm to allow for expansion?

anyone with a driveshaft laying around up for an experiment?

Opinion:
I only know on my on vehicle. The procedure is you push the vehicle back and forth while the nut is tight but not tight enough to keep if from sliding in and our and that centers everything. They you are supposed to tighten it to the specified torque.

The issue there is it is difficult to squeeze under the vehicle and most people don't have that size of wrench that would hook to a Torque Wrench and no room for a torque Wrench. In short I was able to reach with a Wrench and tighten it but not to the specified torque. (One of those procedures that if you had a pit to walk in under your Car would be best. Not sure if you put the Car on a lift if it would the drive shaft would center properly before you tighten the nut.)

If it was allowed to ride freely there would be no need to push the vehicle back and forth.

Also way back someone with an nut that wasn't tighten had worn out splines.

The Flex Discs are mostly rubber and their ability to flex should take care of expansion/elongation of the parts if they are setup properly to begin with.

[Diesel911]

Note that on Cars where the drive shaft splined end just slides into the Transmission Tail Shaft the Splines are exposed to what ever lubes the transmission.

I got a surprise on that one. I did not know the Car I was working on was like that. I detached the U-joint off of the differential end and when I set that and down the Drive Shaft slide out of the Tail Shaft and 2 quarts of ATF I was not prepared for spilled onto the Drive Way before I could even get out from under the Car.

[Usaguy]

Originally Posted by Diesel911

The procedure is you push the vehicle back and forth while the nut is tight but not tight enough to keep if from sliding in and our and that centers everything. They you are supposed to tighten it to the specified torque.

FSM doesn't say anything about that it just says to tighten the nut

Originally Posted by Diesel911

In short I was able to reach with a Wrench and tighten it but not to the specified torque.

I may have over-tightened mine and I have a vibration at 80 mph but only when the outside temp is above freezing if its below then I can go even faster without vibration (3.46 axle so lots of rpms)

[Diesel911]

Originally Posted by christuna

FSM doesn't say anything about that it just says to tighten the nut

I may have over-tightened mine and I have a vibration at 80 mph but only when the outside temp is above freezing if its below then I can go even faster without vibration (3.46 axle so lots of rpms)

There is much missing from the CD Manual. However, I don't know if it was ever in the FSM or not. More then one Member on the forum said it is in the manual for the older non-W123 300Ds. They said that since the driveshaft set up was the same the procedure should be the same. To me that was logical so I repeat what they said and I practice it.

I don't think that over tightening it would be an issue unless you actually bent something.

Concerning the FSM I have the paper manuals and there is stuff in it that is not on the CD and I found out on the CD there is stuff on it that does not show up in the interactive menu.
On top of the Member Stretch has the German Version on I think it was CD and has that it even has the Transmission rebuild info not on the CD I have and in fact the front end alignment specs are not in the CD set I have but are in the paper manual.

Clearly rolling that car back and forth before you tighten the Clamping/Collar Nut is not going to cause any harm and it seems logical to do the rolling if you can.

It is either good or unfortunate I don't have experience with the newer then my 1984 300D.

[Usaguy]

I just read a manual for a 3 piece driveshaft for a W115 and it says that they want 30 - 40 nm for a front nut and 200 nm (!) for the rear one.

does that mean that if one is sliding then the other one doesn't have to be?

Still maybe someone on here with a driveshaft out can tell us for sure.

[hercules]

The Nut almost never needs to be loosened,no one at the Dealer I was employed at ever did. Never sat car on ground and moved back and forth. No complaints.

[Usaguy]

Originally Posted by hercules

The Nut almost never needs to be loosened,no one at the Dealer I was employed at ever did. Never sat car on ground and moved back and forth. No complaints.

Thanks for your input.

[okyoureabeast]

Depending on the model year, your shimmy might be caused by the shafts not being aligned at the proper alignment marks.

You'll need to check the FSM, but there are machined scribe marks on the drive shafts that will tell you what is balanced. Be forewarned however, that before a specific year, the marks were there but Daimler didn't use them.

They look like this:

-

< Rear of car
-

So long as that arrow is between the two marks your fine.

[Usaguy]

Originally Posted by okyoureabeast

Depending on the model year, your shimmy might be caused by the shafts not being aligned at the proper alignment marks.

yes I know about those marks and my car has them

I think it's cars made before 1982 that don't

I have a rebuilt and balanced driveshaft both flex discs, good engine mounts and good sub-frame mounts

I will loosen up that center nut tomorrow or on thursday because I think I over-tightened it.

[Diseasel300]

How'd your U-joint? Stiff or notchy? The vibration in my SDL was from a stiff U-joint. The difference that a new driveshaft brought was profound.

[Usaguy]

Originally Posted by Diseasel300

How'd your U-joint?

brand new, rotates nicely old one was notchy

[Usaguy]

I loosened up my driveshaft nut today (it was way too tight) and I tightened it to about 30nm and after a high speed drive I have to say that my car feels smoother.

So to answer my original question:

Originally Posted by christuna

are the splines supposed to move in and out on the driveshaft with the nut tightened to factory 30-40nm to allow for expansion?

Originally Posted by hercules

The Nut almost never needs to be loosened,no one at the Dealer I was employed at ever did. Never sat car on ground and moved back and forth. No complaints.

Yes

the big nut is there only to prevent wear on the splines but it has to be loose enough to allow the driveshaft to slide in and out.

[Diesel911]

Originally Posted by hercules

The Nut almost never needs to be loosened,no one at the Dealer I was employed at ever did. Never sat car on ground and moved back and forth. No complaints.

You can't change the Drive Shaft Support and bearing without loosening the nut and you need to collapse the drive shaft to remove the inner rear control arm bolt on aW123. I don't think you can change the flex discs without collapsing the shaft either.

In post #3 there is a picture of one of the drive shaft alignment pins and the shaft has to be collapsed enough to clear the pin in order to remover and install new flex discs.
w123 Flex Disc Recommendations??

In post #4 is picture where I needed to remove the right side inner control arm bolt to change the bushings on the control arm.

I tried loosening the flex disc and prying it out of the way with no luck. I also worried the prying was going to damage a 2 year old flex disc.
If it is an an old flex dic they are going to be too stiff to pry out of the way.
sub frame replacement?

[hercules]

Originally Posted by Diesel911

You can't change the Drive Shaft Support and bearing without loosening the nut and you need to collapse the drive shaft to remove the inner rear control arm bolt on aW123. I don't think you can change the flex discs without collapsing the shaft either.

You're right. Those who lack experience probably can't. Here's how: If drive line is ready to come out, tap on back end, and drive line will slide apart. If changing the center support because it's torn, grab drive line once apart and give a couple good yanks and it will come right out of the car. Going back in, lube splines, center splines, and make sure it is straight and start tapping back in. Bolt up. I've done this many times. Hope you can find a way also.

On removing flex disc, they may be difficult but I've never ruined one yet. It's all in knowing how. (experience)