Niesel Transmission swap
 

Hello,
its been a while since I posted on this forum, but I have always found more information here than any other place, manual ect.
I have a 1984 Nissan 720 4x4 pickup truck frame that I installed a turbodiesel from an 83 300d. I installed the MB eng and trans as one unit because they were designed to work together and I really didnt want to deal with trying to adapt something to it. Once the MB powertrain started going in the frame, it was like it was made for it. I will say that it was challenging at times, but it has been the best DD pickup truck I have ever had , pulls great and very dependable when The alt fuel system is taken out of the equation.
I have one slight problem with it, the trans is geared too low for this application. The differential or the donor 300d was somewhere around a 266/1 I think and the differentials on the nissan truck are 3.889/1 so I can go 60 mph, but that is at the top of the comfortable speed, anything faster and Im spitting fuel out the tailpipe.
The transmission is beginning to make noise at approx 320k miles and I know I will have to replace / rebuild it soon so my question is: What transmissions will fit this engine? I would like to find a trans from another MB that might have a higher gear ratio , even if it was a manual trans, I would prefer an auto, but I would do it to see this engine operate at its full potential. As it is now, Im in 4th gear at 40mph. Any suggestions will be appreciated. The numbers off of the engine just below the #5 GP are
617-952-12-042-128 and I dont have the numbers off of the tranny handy, but I can get them. My preference would be to find a 4spd auto from a 300 or 450 sel or some other gas engine MB that would share the bolt pattern and have a slightly higher gear ratio like an OD that is actually over the drive ratio like .85/1. The trans in it now has a 4th of 1/1. Also the gas 300 s and 450 sels are much more common in the junkyards. Thanks in advance, I would have never been able to build the truck in thte first place without this forum.

722.303 is your best bet for an OM617a - 722.315 is also a possibility - these are 4 speeds. If you want to change the gearing ratios you are better off changing the differential as an "overdrive" 5th gear wasn't fitted to MB transmissions until the 722.5. This is super rare and I think was only fitted to petrol engines so you'll have troubles getting it to fit to the OM617. 722.6s are next but then you've still got the problems of fitting to the OM617 again...

The 722.0 / 722.1 / 722.2 (if you can find one!) / 722.3 / 722.4 transmissions are all hydro-mechanical (often with vacuum) transmissions. After that MB moved towards electric / electronic control.

The problem with a differential change is that he has a 4wd so it would require a double differential change otherwise the 4wd won't work. I'm not aware of an overdrive tranny that fits the 617. What about some kind of aftermarket splitter that would allow overdrive in 2wd but keep the original ratio for 4wd. Then you could continue to use the standard 617 diesel trannies.

True true - bigger wheels then?

It would seem that the transfer case must have been located remotely from the transmission. If there is enough space in the frame, the transfer case could be moved rearward, and an auxiliary overdrive unit such as a Laycock from Gear Vendors be placed between the transmission and the transfer case.
Alternatively, both differentials can be re-geared to a taller ratio; perhaps in the 3.00 to 3.30 range.

Off the immediate subject, Army mentioned "722.2 (if you can find one!)". I have a freshly rebuilt 722.2 looking for a home. No. Calif.

There is the elusive five speed manual that fits the 617. You should be able to find one for less money (but not a lot less) than a Gear Vendors overdrive.

Is 5th gear an overdrive in the 5 spd?

Yes it is look for this transmission #717400

A 5spd from an MB van may be better if 5th is overdrive in that too.

I don't think that the 5 speeds of W123 vintage were any stronger for vans. I've been reliably informed that the Getrag 5 speeds are not as sturdy as the ZF 4 speeds (Taxi drivers didn't want them - but then they probably only used 2nd and 3rd!)

To the OP....what size tires are you running? I suspect you may be overly concerned about the rpm of the motor.

So what if it smokes a little on the highway? That's pretty normal for these old all mechanically injected motors.;)

I'm thinking the only inexpensive solution to this is larger wheels and or tires.

Though some transfer cases may be able to change ratios too.

It may be a possibility to adapt to a 22R bellhousing, then bolt a toyota supra 5 speed manual to that, a R151 I believe. That transmission had also been used in 4wd vehicles, so a transfer case shouldn't be to much of a problem. Also it can be found with a .83:1 overdrive.

Mercedes Diesel Engine Adapter Kits

I'm not affiliated with this company.

Appears to be an expanding variety of adaptors to mate the OM617 to a variety of different trannies.

Nice link - it looks like there's going to be a hole where the start goes though...

thanks for the super fast replies, I posted this but havent had time to check it until after the holiday weekend.
Yes changing the differentials are not an option because there are 2 of them and I really wouldnt mind it on the straight rear axle, but the front diff with its offset IFS system (nissan being one of the first to offer it) would be a major undertaking. Not undoable, but maybe beyond the point of diminishing returns. I can find no vendor that makes aftermarket ring or pinion gearsets for the nissan 720 pickups, and most of those aftermarket sets for toyo are to lower the overall ratio for off road, Ive never seen one to raise the final drive.

The tire size are 31 x 10.5 x 15 which are right on the ledge where any larger and the tire vendors start to suffer from insanity when they price them, and it would Drastically alter the road performance, plus Im already rubbing a little on the front tires, I really dont want to increase tire size, that would be about a thousand dollar fix.

Yes this model did have a divorced t case and trans. I did design a 2 speed gearbox to be installed between the t case and the trans, using a set of planetary gears, but the simple machine tools I have were not precision enough to make it work totally balanced.

Even the most modestly priced aftermarket OD gearboxes are waaaay outside the reasonable price range, but that would be the easiest answer to the problem. I even looked for a jeep t case with the little "kit" that changes the input shaft to a set of planetaries. So since I might have to replace the tranny anyway. I figured that I might run it by you guys and see what my fit options are.

I guess my first choice would be to find a mb trans that would bolt up directly to the bellhousing from another model that, while still being a 4spd, would have a significantly taller final gear. For instance the trans I have in it now is a 4spd with 1-1 being its final. If I could find an MB 4spd with 4th being .85 - 1 then it would accomplish the same thing. While there are 4spd trannys all over the place they still have overdrive, they just use 4th as the od instead of the manual trans using 5th. THat would be my first choice and the easiest fix, I would think they would have such a transmission in some of the gas sedans, and if I could find out which transmissions would bolt up to my 617 turbodiesel, I could search gear ratios until I found one closer to my liking.

Short of that, I guess my second preferance would be to come up with an adapter plate to adapt to another relatively modern 4spd auto with OD and a lockup torque convertor, might as well get all of the advantages.
Its just that I went through a time that I was ready and willing to fab or adapt anything to anything, hence the MB diesel in a Nissan frame with a Mazda body - basically all the leftovers, but now, Im trying to avoid the heavy fab work for a while.
The RPMs I am looking for are right in the sweet spot 2500 to 2800, so if I can get 75mph at those rpms ill be happy. I think redline on this engine is just over 5k, but I dont want to get anywhere near that for a sustained period of time.
The nature of the diesel dictates it needs to be run at or around that sweet spot to get max efficiency , power, longevity ect. Thanks for the replies and the ideas, I could not have even built the Niesel without ALOT of help from this forum.

here are a couple of pics of the Niesel or frankentruck

Nice truck - but now we've got another dimension to your problem - it has to be cheap too...

As far as I know the top gear on the 4 speed transmissions (automatic or not) are all 1:1

I guess an overdrive is going to be your best option but I imagine the RPM range you want at 75 mph would only be good for a flat place (like where I live!) - a hilly place would probably cause the engine to bog down or an automatic transmission to change down. I don't know this for sure - you need to get in touch with people who have done this conversion before. I'd expect an OM617 in a truck to be revving closer to 4K at 75 mph...

Check out some MB repowers on dieselbombers.com and I think you will find that your desire of 75 mph will require a higher rpm than 2800 out of a stock '83 Om617 with the size truck and tires your running. Most of the Jeep 617 repowers go for a differential gearing of around 4.10 with an overdrive tranny. Your vehicle requires more power to push it down the road at 75 than the 300D the OM617 was designed for.

I salute your resourcefulness!

Thanks for all of the information, I think that adapting a toyota trans is becoming the most attractive option, if I can get one on there that has either a 4th (auto) or a fifth (manual) at or around .83 or taller, my math says I should be around 74.26 mph @ 2850rpm and that is doable. Yes one of the qualifications for any fix applied to this truck is that it has to be cheap, I dont mind spending money on it, but if you drop 300 here and 500 there before you know it you have 6 or 7k in building something that you could have bought (dodge cummins) for around 8 or 9k , it defeats the purpose.
Anyone have any experience making adaptor plates, I was thinking a 1/4 sheet of steel. I could cast an aluminum one, but I cant machine anything that large on my lathe.
Im not sure I agree about the power, while the larger that a 300d tires will require more power to move, it is also geared lower which will have the opposite effect of the tires, also the relevant specs on the MB 300d are:
3582 lbs / 123hp / 181# torque

and the niesel
3600 lbs / 103hp /134# torque

so these vehicles are comparable, but you are right the larger tires will require a little more power, but the extra torque (35% more) should offset it a little, I know I wont be breaking any land speed records in it, but I think it will get up to speed

I didn't realise the two vehicles were so closely matched in terms of weight and power - I think you're probably on to something there. Your prediction will probably be closer to yours than mine. Let us know how you get on won't you?

I've heard of a Volvo OD unit that can be adapted inline, I odn't know any more details than that...sorry..

If you concidering the Toyota Transmission, 4x4labs makes a nice adapter kit. Uses the toyota flywheel, meaning a clutch job would be at toyota prices aprox 100 for a clutch and pressure plate kit. much cheaper then a MB manual setup.

OM617 to Toyota W56 5 speed adapter kit | 4×4 Labs

http://www.4x4labs.com/wp-content/up...3/DSC_0597.jpg

I'm not offiliated with these guys, but I think they make a Nice product.

Combine that kit with a dual transfer case from these guys and you have my dream power train for a small truck.
Marlin Crawler, Inc. | Originator of Rock Crawling (since 1994)

http://www.marlincrawler.com/sites/a...rofile_640.jpg

My step sisters uncle is the owner of Marlin Crawler, they also make nice parts.

Not to hijack this post, but if anyone can find an adapter for a '87 603 to a 4 spd auto locking torque converter, I'd be interested. I still have trouble understanding why MB did not include a locking torque converter in these earlier vehicles. GM & Ford did...

Ok I think I have decided on a 700r4 4spd auto with lock up torque convertor. Its a GM and they are in alot of 83 to 92 GM cars, they are a dime a dozen here. The gear ratios are 3.06/1.62/1/.7 and 2.29 dang near perfect. So at 2500rpm, I should be at 79.13 mph
(2500/.7/3.889 x 91 x 60/12/5280= 79.whatever) man that would be perfect. If you guys want, I will take pics and post them on this little endeavor.
If anybody has any experience with this particular trans. please share it good or bad

We always like pictures - so your effort will be appreciated.

observe the bizzare mating ritual of the mercedes and chevy. Got the new lock up tc installed, now just modify the adaptor plate

I now have a headache.

Yep, me too, but it will ease a little after the job is complete

Well, I finally got the 700 r4 gm trans adapted to the rear of the 300d eng, and I like it . It took way too long, but it is a good match for the engine against the differentials in this truck. I had a few issues with the throttle cable, but I drilled a couple of holes in the throttle plate on top of the valve cover on the 300d so I could change the leverage / geometry and I think Ive got a pretty good set up. If anyone needs any information on this kind of swap, please dont hesitate to ask.
Thanks again for all of the suggestions. If I can offer something back to the forums, I have come up with a way to stop buying these waaaaaay overpriced underfiltering, restrictive secondary fuel filters if anyone is interested, but I think I should start a new thread so I will place a link to it later from here

May not be anything you are interested in but GM made a 4 speed overdrive Manuel trans in 1981 and I'm sure some other years. I have one I put in a 1964 Chevelle SS with a 283 ci that makes a super road car. 1,2, and 3 are great for city driving and 4th is great for 70-75 (or more). The chevelle has a 3:08 and the truck the trans came out of had a 2:56. The truck was useless below 60 mph in 4th. Just a thought.

Paul

I fixed it!:D