108 drivetrain question - PeachParts Mercedes-Benz Forum

deferr · #1 11-15-2005, 11:52 AM

I'm in the process of a 350 swap in my 68 108. If originally had a straight six gasoline engine, manual tranny, and 4.11 rear end (I beleive). I am a bit concerned that if I add too much power to the 350 that the rear end and tranny won't hold up.

Does anyone know what the practical hp rating on these are?
Are they the same equipment used on the 4.5s?

p.s. Don't try and talk me out of chevy power. I agree that mercedes power would be cooler but I'm a college student working with a budget and when you want a little more power for cheap a 350 is a great way to go. While they will not go for as long as a mercedes v8 they are a very trusty motor.

Tomguy · #2 11-15-2005, 03:36 PM

The rear probably won't have a problem, but you definetly will want a taller gear so you're not turning so many RPMs on the highway.
As for the tranny, I doubt it. Someone else might be able to answer you better, but if you want a Benz tranny, you'd probably need one out of a 3.5 or 4.5 to hold the power and keep it together.

Ara T. · #3 11-16-2005, 01:00 AM

It might help to tell us how much hp/tq the 350 will put out, I haven't really seen any that put out stock horsepower, whatever number that may be.

billrei · #4 11-16-2005, 02:14 AM

I would have thought a smart college student would have researched all this before starting the project...and you state you are going this route to save money!! I would think the cost of fabricating special motor and transmission mounts, custom oil pan, custom headers and exhaust system, custom driveshaft, custom cooling system and making all the linkages etc. would far exceed the cost of a good used M108 motor...Actually if you used a small block Ford motor you could avoid the custom oil pan....

deferr · #5 11-16-2005, 11:41 AM

I haven't starting inserting a motor yet. I don't even have a motor yet.

This is my research but I have started the project because the car is being completely stripped and all rust cut out and replaced by brand new metal.

I am in college and I am intelligent and considering I have all the tools necessary at the machine/welding shop I work at I beleive a 350 WILL be cheaper.

The only piece of the car I am going to do "out of house" is drilling the chevy flywheel to match the mercedes torque converter, but BEFORE I spent hours finding a motor and fabricating motor mounts, headers, etc. I decided to ask the mercedes experts on how much hp I could bring the 350 to without overloading the tranny and rear end.

As for fabricating. I LIVE to fabricate. I fabricate all night at work and on the weekends when working on the car. I'm not interested in a stock 108 when I'm done I'm interested in my own car with my own lines, and since mercedes engineering is outstanding right off of the show room floor a custom mercedes only seems reasonable.

There is a place for original equipment and I respect it. I just find it boring. So hopefully somebody has some numbers for me? I'm asking a simple question how much hp will the tranny and rear end practically handle? Let me worry about the fabrication and details.

WANT '71 280SEL · #6 11-16-2005, 12:19 PM

Dan, I would assume the rear end would hold up well and I would just try the tranny. If it only lasts 50k miles it won't matter because you probably won't drive it that much.

How's the rest of the progress coming along?

Thanks
David

EDIT: Just an afterthought of mine, but a 4.5 has a 3 speed tranny and you definitely don't want that. If anything, a 420/560 tranny would be a good candidate but just keep with what you have and if problems arise, then get a Chevy tranny.

deferr · #7 11-16-2005, 01:09 PM

2 door frames are welded and 2 more to go. Then I can skin them.

WANT '71 280SEL · #8 11-16-2005, 02:22 PM

Cool, you need to update your website since I check it a couple times a week and never find anything! Have you welded anymore body panels or gotten into the floors?

Thanks
David

Mark DiSilvestro · #9 11-16-2005, 07:14 PM

Do you have a tranny yet? You said the original MB box was a manual. I think your best bet would be the tranny and rear end from one of the V8 sedans. The rear end would have to be from a W108 as it's the only V8 model with a compatible swing-axle rear. If you insist on a MB autobox, you could try one from a W116 450SE or SL as those might be easier to find. But why not just use a GM tranny, such as the 350 Turbo-Hydramatic?

Happy Motoring, Mark

WANT '71 280SEL · #10 11-16-2005, 11:03 PM

He has the 4 speed auto from the original 250S. So, it's not a stick. The thing about the V8 transmissions is that they're 3 speed and would kill the power

Thanks
David

billrei · #11 11-16-2005, 11:07 PM

Whatever dude... The drivetrain from a 6.3 will handle 250 HP it also has a final drive ratio of 2.63:1 and a limited slip diff. I would also go with the GM auto trans as previously suggested. Check out this site http://www.johnscars.com/default.htm They do Chevy conversions in Jags and other makes. They might be able to provide some tips.

Tomguy · #12 11-16-2005, 11:33 PM

Your best bet is probably a 3.5 or 4.5 rear if you are putting a Chevy V8 in. You obviously don't want top end speed but rather off the line oomph, so a 3.5 would be better (it's shorter than a 4.5's). The rears won't be a problem but I really think that stock Benz tranny can't handle over 200HP. One from a 3.5, 4.5, or 6.3 would without a doubt.

Mark DiSilvestro · #13 11-17-2005, 12:29 AM

Quote:

Originally Posted by WANT '71 280SEL

He has the 4 speed auto from the original 250S. So, it's not a stick. The thing about the V8 transmissions is that they're 3 speed and would kill the power

Thanks
David

Well, he did say in his original posting that it came with a MANUAL tranny.
In any case, My reference list the 4 speed automatics being used only in the sixes and 3.5 and 6.3 V8s. After '72, the V8 4-speeds stayed in Europe. The majority of 1970s US market V8s, including the W116 450SE/SL had the 4.5 with the 3 speed automatic,
and, with Chevy power, why not simply go with one of the Turbo-Hydramatics?
Also reveiw the 'Sticky' about the Chevy-powered Mercedes on this Forum.

Happy Motoring, Mark

WANT '71 280SEL · #14 11-17-2005, 10:29 AM

hmmm. I just now noticed he did say in the original post that it is a manual transmission but when I looked at his project with him I thought it was auto. I think he may want to go with a Chevy tranny after all. The thing is though, would it matter that much if it were a manual tranny? I would think being a manual it could handle more of a power range.

Thanks
David

deferr · #15 11-18-2005, 01:18 PM

sorry about the delay in responding school has been kiling me. I do have the AUTO tranny. my original post was a typo sorry about the confusion.

so i'm taking it that a gm tranny and my stock 108 rear end may be my best bet???