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.

__________________
1992 W201 190E 1.8 171,000 km - Daily driver
1981 W123 300D ~ 100,000 miles / 160,000 km - project car stripped to the bone
1965 Land Rover Series 2a Station Wagon CIS recovery therapy!
1961 Volvo PV544 Bare metal rat rod-ish thing

I'm here to chat about cars and to help others - I'm not here "to always be right" like an internet warrior



Don't leave that there - I'll take it to bits!

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.

__________________
1977 300d 70k--sold 08
1985 300TD 185k+
1984 307d 126k--sold 8/03
1985 409d 65k--sold 06
1984 300SD 315k--daughter's car
1979 300SD 122k--sold 2/11
1999 Fuso FG Expedition Camper
1993 GMC Sierra 6.5 TD 4x4
1982 Bluebird Wanderlodge CAT 3208--Sold 2/13

True true - bigger wheels then?

__________________
1992 W201 190E 1.8 171,000 km - Daily driver
1981 W123 300D ~ 100,000 miles / 160,000 km - project car stripped to the bone
1965 Land Rover Series 2a Station Wagon CIS recovery therapy!
1961 Volvo PV544 Bare metal rat rod-ish thing

I'm here to chat about cars and to help others - I'm not here "to always be right" like an internet warrior



Don't leave that there - I'll take it to bits!

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.

__________________
Whoever said there's nothing more expensive than a cheap Mercedes never had a cheap Jaguar.

83 300D Turbo with manual conversion, early W126 vented front rotors and H4 headlights 400,xxx miles
08 Suzuki GSX-R600 M4 Slip-on 22,xxx miles
88 Jaguar XJS V12 94,xxx miles. Work in progress.

Is 5th gear an overdrive in the 5 spd?

__________________
1977 300d 70k--sold 08
1985 300TD 185k+
1984 307d 126k--sold 8/03
1985 409d 65k--sold 06
1984 300SD 315k--daughter's car
1979 300SD 122k--sold 2/11
1999 Fuso FG Expedition Camper
1993 GMC Sierra 6.5 TD 4x4
1982 Bluebird Wanderlodge CAT 3208--Sold 2/13

Yes it is look for this transmission #717400

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

__________________
1977 300d 70k--sold 08
1985 300TD 185k+
1984 307d 126k--sold 8/03
1985 409d 65k--sold 06
1984 300SD 315k--daughter's car
1979 300SD 122k--sold 2/11
1999 Fuso FG Expedition Camper
1993 GMC Sierra 6.5 TD 4x4
1982 Bluebird Wanderlodge CAT 3208--Sold 2/13

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!)

__________________
1992 W201 190E 1.8 171,000 km - Daily driver
1981 W123 300D ~ 100,000 miles / 160,000 km - project car stripped to the bone
1965 Land Rover Series 2a Station Wagon CIS recovery therapy!
1961 Volvo PV544 Bare metal rat rod-ish thing

I'm here to chat about cars and to help others - I'm not here "to always be right" like an internet warrior



Don't leave that there - I'll take it to bits!

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.

__________________
[SIGPIC] Diesel loving autocrossing grandpa Architect. 08 Dodge 3/4 ton with Cummins & six speed; I have had about 35 benzes. I have a 39 Studebaker Coupe Express pickup in which I have had installed a 617 turbo and a five speed manual.[SIGPIC]

..I also have a 427 Cobra replica with an aluminum chassis.

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.

__________________
1984 300sd auto with 246,000 miles

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.

__________________
You can't always get what you want, but if you try sometime you just might find you get what you need.

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

__________________
1992 W201 190E 1.8 171,000 km - Daily driver
1981 W123 300D ~ 100,000 miles / 160,000 km - project car stripped to the bone
1965 Land Rover Series 2a Station Wagon CIS recovery therapy!
1961 Volvo PV544 Bare metal rat rod-ish thing

I'm here to chat about cars and to help others - I'm not here "to always be right" like an internet warrior



Don't leave that there - I'll take it to bits!

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.