Would it be possible?
 

This is something I have been thinking about for quite some time. Would it be possible to swap between the insides of a diesel 4 speed transmission to a gasser 5 speed like one from a 190E? The exterior of both cases look the same except for the starter humps. The 5 speed gear housing looks like it just bolts on to the regular 4 speed housing. I'd go further but I don't have any FSM's on these transmissions to even attempt their disassembly.
Here are the two transmissions side by side.
http://i131.photobucket.com/albums/p...i/IMG_2604.jpg
http://i131.photobucket.com/albums/p...i/IMG_2605.jpg

This kind of idea could possibly solve the problem of getting a rare 5 speed transmission if someone is capable of doing this.

Not a bad ideal. Unless someone has attempted this before I imagine it is an unknown senario. One thing might be to compare the casting numbers on the two forward cases. If the same it greatly increases the possibility in my opinion. Of course with the belhousing cast with the forward case and the starter hump on the opposite side the numbers unfortunatly will be different.

Or if the two case numbers are found to be otherwise interchangeable. A question on the german site might bear fruit as really there have been a lot more manual transmissions in europe.

Another thought is the ideal of cuting off the starter hump and moving it using an alignment jig. Perhaps not too difficult if otherwise the bellhousing is the same. Basically if all the holes lined up with the jig and the surface was flat it might work well. All that might be required then is a piece of steel with all the belhousing bolt holes for the bolts drilled out. This of course from the 616-617 belhousing flange. You could start out with a paper pattern of the holes locations for comparison. At least that might show if moving the hump it is remotely possible.

Bolt the cut off hump to the plate with the later bellhousing and weld away if otherwise simular. Good thinking of you to think of a possibility as I too really want a five speed for one of my 240s. This is the kind of thing that can be missed by people quite easily. Usually turns out impractical but not always. Keeep us informed if you even just try the hole matchup senario or find case interchangability information.

It is quite possible they just for our purposes might have changed only the bellhousing part of the casting. It would have cut tooling and production part costs down on internal parts. Another way to check this out is to compare internal part numbers in both cases from manuals.

If the exact same part numbers you have your answer. Perhaps one of our members has the internal part numbers for both transmissions parts?

Cutting it off an rewelding the hump would sound easy but the rest of the bolting pattern is way different between the two. I've checked with a spare 616/617 intermediate flange, way too different.
The only breakdown of the transmissions that I have is in the Hanes book and it leaves much to be desired. I've heard about CD versions of the FSM for transmissions but I have yet to even locate one of those.

Thats too bad the bellhousing pattern is different totally. It might have been very easy otherwise. Since mercedes was such a low volume producer there is still a chance the internal part numbers might be the same.

That is the safest way to approach this in my opinion. Especially if the basic gear ratios remained the same for both transmissions then it is easy. If not it becomes complicated somewhat again.

This said there is still a small chance of simularity. Cost of re tooling is substantial if not required. They just might have gone the cheaper route.

I was reading in one of the threads that the gear ratios are different between the 4 and 5 speeds in the first four speeds. Sounds kind of odd why that would be.

Someone is already doing this. I think on Benzwhirled. And running into all kinds of unforseen circumstances. But, I am pretty sure he's persevering through it.

If I had the shop manual for these transmissions, I'd give it a try.

DJ, what have you come up with? Or did you just shelve the project?

Check out this thread where the guy is really digging into making a 190
5-spd fit into a 123.

http://www.superturbodiesel.com/std/617-franken-5-speed-t-323.html

He is getting close to making it happen. he has been swimming through
unchartered waters here.

Charlie

Yeah, I pretty much shelved the idea. I've actually moved my interests toward my Cummins diesel and won't be putting anymore effort into my 300D. Not that there's anything wrong with the 300D except for an inop A/C. It's still a great car. I've found that the Dodge Cummins will be much more practical for me for now. Surprisingly the fuel economy with the Cummins is pretty good. I'm only sacrificing a few mpg's from what the 300D got.