240D manual to 300D manual conversion - PeachParts Mercedes-Benz Forum

diesellieber · #1 08-31-2004, 02:37 AM

Ok, I've got the 300D in place but the rear transmission mount doesn't fit the bolt holes, and the driveshaft is about 4 inches too long. So, I shoved the 240D to the side while I look for an easy (cheap) way out.

Then I get involved in switching out the automatic trans on the 79 300SD with a parts car that I picked up at the salvage auction. Hmmmm... interesting.... the transmission mount out of the 79 300SD has 4 bolts going into the frame instead of two and big huge slots for transmission position adjustment. And, the driveshaft looks like looks like it is about 4 inches shorter. Can anyone think of a reason why this isn't going to be my cheap and easy solution???? The rear transmission mount looks like it will be much easier to modify than the one out of the 240D.

I bring this up, because someone here (sorry, I forget who) said I would have to pay a hundred Plus bucks to get the old driveshaft shortened. Did I stumble onto a good solution?

R Leo · #2 08-31-2004, 03:48 AM

Too bad you didn't search the Forum first.

There's a pretty good write-up about swapping to a manual transmission.

diesellieber · #3 08-31-2004, 02:13 PM

Actually, I'm not converting to a manual transmission. The car already was a manual transmission. I'm just putting in a 300D that came out of a manual transmission car. Since the motor is longer, it moves the transmission rear mount and requires the driveline to be shortened as well as the linkage from the shifter. I searched and found info from someone who had done this. His description included taking the driveline to a shop and having it shortened and balanced for a hundred plus bucks. I just happened to notice that the driveshaft out of my 79 300SD W116 chassis seems to be the right length to work in a W123 chassis with the 300D and the manual transmission. If the the splines on the driveshaft are the same, it should work. I'll know as soon as I get my 300SD off of the lift.

I just wanted to let everyone know that they might be able to save the bucks required for steps 24 and 25 of your post. Driveshafts from W116 300SDs are possibly easier to find than driveshafts from manual transmission W123s.

leathermang · #4 08-31-2004, 02:52 PM

That also is available already posted... Ben Ridge did it...and several others... very specific advice posted about the upgrade to 5 cylinders...

diesellieber · #5 08-31-2004, 05:53 PM

yep, already read all his stuff... He's the one who said you need to have your driveshaft shortened for 125 bucks.

My question is if anyone knows whether or not a 79 300SD driveshaft will work. I measured one and it is about 5 inches shorter than the 240D driveshaft. As soon as I can get the car back on the lift, I'll try it. In the meantime, I thought someone here might know. Couldn't find anything in the archive about this.

Old300D · #6 08-31-2004, 07:16 PM

Quote:

Originally Posted by diesellieber

yep, already read all his stuff... He's the one who said you need to have your driveshaft shortened for 125 bucks.

My question is if anyone knows whether or not a 79 300SD driveshaft will work. I measured one and it is about 5 inches shorter than the 240D driveshaft. As soon as I can get the car back on the lift, I'll try it. In the meantime, I thought someone here might know. Couldn't find anything in the archive about this.

I can't answer your questions, but I've read most of the conversion threads. You may be the first one I've heard to try to convert a W116 ('79 300SD, right?) to a manual, but if you can get the tranny mount right, you may have to shorten the driveshaft.

boneheaddoctor · #7 08-31-2004, 10:41 PM

I would love to do a W116 manual conversion.......but I am not a trailblazer as I don't have easy access to all the parts most of you guys do.

MMMMMMMMM 1979 300SD 5-speed.......that would be so cool.

notlostmaybe · #8 08-31-2004, 10:48 PM

i know from my recent 280c manual to 300cd turbo manual conversion that the coupes driveshaft will work without modification.

don

diesellieber · #9 08-31-2004, 11:22 PM

I'm having a hard time making myself clear here it would seem.

A) I'm not converting anything to manual. The 240D already was a manual, and the 300D I put in it also came out of a manual. Unfortunately, I don't have the driveshaft from the 300D so I need a shorter driveshaft than what the 240D has because the engine is longer and pushes the transmission back about 4 inches. The documented way to do this according to the archive is to just take the 240D driveshaft in and have it shortened and balanced for about 125 bucks according to Ben Ridge's post. I was planning to do this.. but stopped working on the car till I get around to it.

B) My 79 300SD (W116) has a new engine, but the transmission slips in high. I am only trying to replace the automatic in it with another one. I found a wrecked 300SD at the local salvage auction and bought it for the transmission.

After I pulled the engine and tranny from the wrecked 300SD, I noticed that the driveshaft was 5 inches shorter than the 240D driveshaft that is waiting to be shortened. It would seem that this might work instead of shortening the 240D's driveshaft. I couldn't find any mention in the archive of anybody having tried this before, so I thought someone might be able to tell me here that it would work.

That's what this thread is about.

leathermang · #10 09-01-2004, 07:31 AM

We are simple folks here....and you included some extra visual images...so we got confused....
There is a chance that will work.
Are the connection methods for the front of the shaft and the output of the transmissions the same ? Both use the flex disc ? etc..? How close did you measure that 5 inches.... ? You said ' about' earlier.... hopefully it is closer to 4 inches... Ridge said the difference in the shift linkages was exactly 4 inches I believe....so I would assume this is also the magic number further back in the system....

On old regular cars it would be less problem if there really is a one inch difference from one to the other..... as they used slip yokes to let the wheels move up and down... but with the MB system you have a critical distance on the front and rear driveshafts which may not allow you to interchange them.
Looks like you will be the pioneer on this one....

diesellieber · #11 09-01-2004, 10:37 AM

Quote:

Originally Posted by leathermang

Looks like you will be the pioneer on this one....

Yeah, I was afraid of that. I don't remember how much of the driveshaft came off of the spline when I pulled it out, but it wasn't much more than an inch. On the other hand, it seemed like the holes in the frame for the rear mounts were a little more than 4 inches apart. I'm hoping a half inch spacer at the donut connection will give me enough grab at the spline. Otherwise, I might need some help towing the beast home when it goes. I'll keep my laptop and cell phone with me so I can post from the side of the road....

Old300D · #12 09-01-2004, 11:19 AM

The 300D driveshaft is 4" shorter than the 240D unit, and is the ideal shaft for converting a 240D to a 5 cylinder. It's what I'm using in my 240D OM617.952 conversion. The 300D crossmember also bolts up. Remember, the 240D and 300D share the same chassis, so most of the bolt-up stuff will swap.

leathermang · #13 09-01-2004, 12:03 PM

Old300d, Well, were you just letting us sweat.... or did you just run across this thread ? LOL

TwitchKitty · #14 09-01-2004, 01:34 PM

I have a manual 300D, I could measure something if you think it would help.

Old300D · #15 09-01-2004, 03:34 PM

Quote:

Originally Posted by leathermang

Old300d, Well, were you just letting us sweat.... or did you just run across this thread ? LOL

No, I finally understood the question.

I also happen to have both drivelines in my garage. However I steered clear because I am using automatic trannies, and I don't know if the driveshafts are compatible with manual trannies. So there are a lot of variables at work. But if a 116 shaft fits, maybe the regular 300D auto driveshaft will as well. My impression is all the driveshafts are all the same to the rear end, the differences are in the front half.