Topic: 240D manual 4 speed into a 300SD- Discuss!!
 

Have you done this? Do you know someone that has? I know someone who has all the parts needed to do the swap, except the drive shaft. It appears that a drive shaft from a w126 long wheel base would work. The 240D manual tranny is 6 inchs shorter that the automatic from the w126 300SD. My questions are:

1) What problems did you run into?
2) What did you do for a drive shaft?
3) How successful has the conversion been?
4) Would you do it again?
5) What else do I need to look out for?

My car is the '83 300SD. Donner was a 240D with ~150,000 miles on it.

Thanks for the help.

Also keep in mind that that the 240 engine is shorter than the 300 engine... I believe the final difference is actually around 4in, according to the often-done 300d swaps.

If you search you'll see that lots of people did it for the 300d, customizing the driveshaft/shift linkages, balancing 240 flywheel, etc.

As for W126, the LWB deal sounds interesting, but I would imagine that you'd run into more issues overall compared to W123 (will the clutch pedal fit for example).

A lot of people have done similar things.... and many have wound up with vibrations they did not want and have yet to find the cause of and correct.
Also, it is my theory that MB did not put the turbo with the manual transmission for one or more reasons.....many dispute my feelings on this...but are NOT able to articulate WHY MB thought they should not be put together...
Since I have read the FSM concerning the flywheels... I would certainly do everything possible to put a 300 flywheel on the 300 engine just like the FSM says to do...
Several have used the 240 flywheel and that MAY account for some of the vibration problems...

What is there to discuss? If you search for "auto manual conversion" you'll find several very detailed threads on this topic and many very happy converters.

Ignore leathermang on conversion topics, he must have something personal against it.

But that would involve no real time interactions with forum members.... only lonely searching in the archives... LOL

Yeah I have read but it is good to hear new thoughts. Thanks for the information.

Its not easy... First if you using an 85 SD, you are going to have to custom make a pilot bearing as the hole is 34mm in diameter rather than 35 mm. Second you will have to do alittle cutting on the 240D pedal assembly, There is no upper hook so you will have to cut that off. The pedal height is different but its managable. You will also have to live with just the 4 booster bolts because the W126 brake pedal assembly has a bracing arm that extends downwards.
The shifter does bolt in but is very short for a W126 console, you will not be able to use a 240D shifter boot or console section The shift rods are all much much too short, so you will have to make new ones.
Now the hard parts. The speedometer in a W126 is electronic, the 240D manual uses a cable. I cut up the W126 cluster to install a W124 Speedo head, you will have to come up with your own solution.
The driveshaft will have to be lengthened, I thought I could use a SDL driveshaft in a 500SEC but i needed to be lenghtened 2.25 inches. I was able to use the 240D trans mount and bracket by drilling extra holes in it.
The clutch hardline had to be made custom because the 240D one did not fit.

Thats pretty much it, Results, its ok, no I wouldnt do it again, I used a 240D flywheel that was suposedly matched to the flexplate, but its not and i have a bad vibration around 1600 rpm and at idle. which is currently set at 850 rpm. I cant start the car on a big hill because I used a 2.24 differntial.

I am going to balance the driveshaft and replace the diff with 2.47 and see if its easier to drive.

So as you can see by the list of stuff I mentioned its alittle more involved that a 300 D conversion.

Not it isn't. The 951 and 952 are the same.

IceFire, Thank you for that very informative and honest post.

That is a very different job than what we used to seeing..... doing this to a 123 where the factory also installed the manual trans in the same model... pretty much a bolt in situation if the donor and patient are both available...

Manuals were also available in the 280SE.

280SE... wouldn't that be a 6 cylinder gas engine with fuel injection ?
Are you saying that would fit something referenced in this thread ?

crashone has a 300SD. Last time I saw one in person, a 280SE was a W126 too.

I just saw this...

There are also many who have vibrations they can not find the cause of..

AND more importantly ... you NOT being able to explain why MB did not put the two together leaves a big chance that my objections are correctly derived from a problem in the nature of PHYSICS involved....and not personal...

You are wrong, in 1985 there was a switch, Please see TOMJ 's swap threads,

I have a 1971 280SE sitting in my driveway...but I don't look at the other numbers often..