Mercedes-Benz Forum banner

M120 Manual Gearbox

22K views 20 replies 8 participants last post by  Steve_B 
#1 ·
This has probably been seen before, and shared countless times (headphone users, turn your volume down!!):

https://youtu.be/wcP-p8Nlbqs

This is my goal for my 500SE.

Score an M120, and use a getrag out of a recent diesel BMW which is a beefy box capable of handling up to 800Nm of torque.

I figure it's better to share this in the 140 section, because it'll be you folks I reach out to for bits and pieces and advice once I finally get a chance to get started on this.

Now, before anyone says "Why would you want a manual V12 in a big car like that?", it's because I just do. My car is a short wheelbase car, and it's very nimble even in its current form. A manual V12 in a luxury sedan just seems right to me.

The idea is to have something super quick, but basically look like a total sleeper, with a manual box for personal driving preference while incorporating a powerful motor for long distance cruising capable of having an abundance of power whenever I need it.
 
See less See more
#2 ·
Sadly the only somewhat affordable V12-manual combination is the anemic BMW 850i/ci (CSi is too expensive to count). If I had found an M120-manual car I would have bought it! I imagine the swap is hilariously costly and difficult.
 
#4 ·
I don't know. The motor would be the most expensive, followed by the gearbox. I have a shop that can fashion me a bellhousing, flywheel, etc., for a good price.

It's definitely been done as evident by this video.

It won't be easy, but I don't think it'll be astronomical either, especially if I can fashion many of the parts myself.

I thought you were hot-rodding a '51 170S?
I am, and that's coming along nicely, finally. Starting the rear suspension work at the moment before moving on to the rest of the drivetrain.

I've already acquired the gearbox, driveshaft to modify, and now I'm waiting on a good motor. PO of the car is very involved in the process as well, and wants to make sure the motor I roll with is all set. I said I don't mind doing a rebuild, but he wants to spare me the work if he can.

There will be a local car show up the road in March, so ideally it'll be ready for that!

I've been very bad about taking pictures of my current progress on that car, but I'll be sharing more as I make even more progress.

The plans for the 500 are something for the future (hopefully sooner than later!).
 
#5 ·
If you can get this done, it would truly be a one-off. I remember reading that the factory has never offered a M120 backed by a manual gearbox. The reason given was that they just could not ensure that any box they have available can handle the torque reliably. It more than likely has something to do with the M120 being in their most expensive cars; and the people who buy them, don't want manuals (for the cost of the car).

I recently did a six speed manual swap into my Volvo V70R. It really woke the car up. I can't imagine what it would do for a V12.

Good luck,
Jason.
 
#7 ·
I mean, I'd love to give the M117 a manual to really wake it up, but I figured by the time I invested all that time into it, I may as well look at getting the motor I really want for it.

There are plenty of manual transmissions out there that can handle these motors, it's just as you said, the customers who wanted these motors wanted automatics considering the cars that these were built in to.

Excellent project, good luck. Not sure if you can contact that Oliver Amon guy directly through his youtube channel for some direct info. He punishes that car and jammed a M120 with manual into a W202, so he probably knows how to get things setup properly!

Engine, trans, engine management, fab costs, elec work, it will all add up.
People have tried, but have apparently gotten nothing. The only confirmed thing from the comments was the use of a BMW transmission from a diesel car.

This motor is old enough that engine management should be able to be handle with MegaSquirt, and I know someone who's very good with it and can help me out with that. Fab costs should be minimal due to being able to do a lot of it myself, same with the electric work.

Biggest costs I can honestly foresee in that regard is the cost of the motor and that of a suitable gearbox.

Automatics just aren't my thing. I don't care that they can shift much faster than I can now, and blah blah blah. It's all about that feel and what I want as a driver.

I drive my 5-speed 190E 2.3-16 daily, to and from class and work, and I enjoy every second of it, even in the horrid San Antonio traffic. It's just a blast to downshift at will instead of mashing the pedal to hit a kickdown.

As for the 170S project, for those who aren't aware, I'm stuffing a Miata I4, likely a 1.6 out of an NA body car, or perhaps a 1.8. I'm getting all the parts I need in working order for next to nothing, so I really couldn't pass it up.

I couldn't justify a period gas/diesel mower, when people were wanting $5000 for something that needed a rebuild and didn't even come with a gearbox. The thought of an OM616/617 or even an M102 crossed my mind, but not very available here (especially with manual gearboxes), and the sizes of the I5 and even the M102 would be pushing the limit likely requiring to cut into the firewall. The space gets too narrow up front for a V6, as I was initially considering a VG30 motor from a 300ZX, but after measuring (have yet to do a test fit, but that should happen this week!), the little Miata I4 will fit the bill hopefully without having to cut into the firewall.

The whole car will need to be converted to 12V from 6V, but I've factored all that in already, and it's not like the vehicle itself has a lot of electrical components anyway.

This V12/manual swap for the 500 won't happen until after the 170S is done unless I get a line on parts for a great deal. I'm already brainstorming with another guy locally who'd be interested in assisting me with this, so if we can make some headway sooner then I'll be all over it.

I mainly wanted to share this awesome video as inspiration that, "es, it can be done!
 
#6 ·
Excellent project, good luck. Not sure if you can contact that Oliver Amon guy directly through his youtube channel for some direct info. He punishes that car and jammed a M120 with manual into a W202, so he probably knows how to get things setup properly!

Engine, trans, engine management, fab costs, elec work, it will all add up.
 
#8 ·
Makes sense, the guy is quite young. I could be wrong but I doubt he does all his own work. If I went to all that trouble and cost and wanted a unique car I'd be reluctant to share info too.

M120 W140 drift car is so badass. :cool:
 
  • Like
Reactions: Josh
#9 ·
It is! I think the M120 is the best motor choice to get into 12 cylinders, without getting into too much tech where you'd be dealing with code after code and what not.

There's been a member over on Peach Parts who swapped an M120 into his 560SL, but he stuck with an automatic, obviously.

I think doing the MS for engine management will cut out a lot of the guesswork and required parts, too.

That's why I'll be looking for an earlier M120 anyway, since I know the later motors were more depending on electronics and receiving "OK" signals and all that jazz.

A lot of work, to be sure, but certainly not impossible!
 
#10 ·
M120 is a monster engine. Same torque as the early Diablo engine with better power band ie. more torque at lower revs, low maintenance, good for high mileage, can be had CHEAP, and that big NA V12 sound if you open up the exhaust.

Just knowing it can push the massive W140 to over 300KPH with the speed limiter removed says a lot.
 
#11 ·
... can be had CHEAP...
That's what makes this idea THAT much more appealing!! I'm meeting more like minded folks as I work on my 170S, and that will help cut down on costs, as well as give me additional help when I attempt to do this.

I love my 500SE more than any 140 (that's a personal aesthetic choice, not saying the 140 isn't a nice car, it is!), but I am envious of that V12.

I mean, there are other V12 choices for me here in the states, but for this car I'd truly like to keep it MB, and the logical choice is the M120!

At the same time, I'd hate to rip apart a good 140 for a motor :crying
 
#12 ·
hello to all pls advise me i have a 92 m120 engine and transmission i want to put this engine and box into a american vehicle my questions are wit it being an early mechanical throttle body and not electronically controlled transmission how hard is it to get running and with which aftermarket ecu is best also things i need to look out for like vacuum routing etc i want to go as simple as possible no abs asr etc just start and go smoothly no major hp gains or anything pls help.
 
#13 ·
You'll need to do a lot of reading. Your primary throttle body is not all mechanical. Only mechanical for a limp mode. The lever on it controls a potentiometer which feeds the EGAS module, which then tells the throttle plate where to move. And the second throttle body for the other bank has no mechanical linkage at all. You would need at least both LH modules, the EGAS module, both ignition modules all of the harnesses and some way of tricking them into thinking that all the interconnected modules, are all working so they don't instantly go into limp mode. It's probably been done, but it won't be simple.

Sent from my Nexus 5 using Tapatalk
 
#14 · (Edited)
You would need at least both LH modules, the EGAS module, both ignition modules all of the harnesses and some way of tricking them into thinking that all the interconnected modules
Jon:
The question was posted in several threads, two on the w140 forum.
We addressed some of the issues here:

http://www.benzworld.org/forums/w140-s-class/2853538-m120-question.html#post16861105

Notice that the intention is to use Megasquirt or alike.

In this case, the throttle bodies can be "converted" to just mechanical plates driven by a linkage. One can come up with some type of Hall sensor as TPS (one or two) and do away with any of the original MB technology for fueling and spark.

Only the MB crank and cam sensors will carry over. Aftermarket MAP/MAF, adjustable FPR and perhaps different injectors. Wide band O2-sensors and a true beast will be unleashed.

As you said -- may been done already, "but it won't be simple"

Steve
 
#15 ·
I was thinking more in terms of things he would need to replace. Another thing is that he would have to come up with a way to control the cam timing solenoids. It appears there is some sort of megasquirt add on to do it, but I didn't research further.

He really needs to fully understand the stock system first, then figure out a way to duplicate the relevant functions.

Sent from my Nexus 5 using Tapatalk
 
#16 ·
hi can you possibly help with this?

its about the mercedes 722.3 on my w140 600 1992 on the right side of tranny it has a white box with 2 vacume lines coming out red and blue and on the other side has a white one for vacume modulater can you explain what the red and blue ones do and also how does the sports and economy mode work thanks and have a great day
 
#20 ·
Take a picture of the switch you are talking about, and post it here. There is an Eco mode switch for the HVAC system. There may be a switch that looks like a snow tire for use with snow chains; my coupe doesn't have that switch. There is also a switch for sport or comfort settings for the ADS ride control. Nothing is marked as you indicate, unless it was added, or a different switch swapped out for the original.

MAVA has posted extensive links to transmission repair/information manuals in this forum. Do a search for them. He may chime in on the white box.

Sent from my Nexus 5 using Tapatalk
 
#21 · (Edited)
are u any good at transmissions i need help with 722.3
If this was directed to me -- no I am not good, but I managed to remove the transmission, take it apart and put it back together. On my own.

http://www.benzworld.org/forums/w14...hic-b3-piston-failure-tranny-rebuildable.html

There is no sport mode on mine and there should be none on your. The closest to sport mode will be the engagement of the kickdown solenoid, but it is only applicable to launches from a standstill.

There are only 2 vacuum lines going to the box, on to the modulator and another one is for the shift-delay.

Good luck,
Steve
 
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.
Top