Hello,

I do have a 1989 Cummins with 727 trans and need to have an OD Transmission.
I know there are some Diesel 518 out there but rare to get one.

I might get A-518 Gasser 46RH Transmission and was wondering if you can morph those two.
Using the front/main case from the 727 with the cummins bellhousing and the tail and all internals from the Gasser 518?
Obvioulsy would need a Diesel Converter due to the different splines and as well the governor from the Diesel.

It's more work than it's worth, Just get a trans that will bolt up to the cummings.

Buy a newer 48RH, not the weak 46 RH or whatever the proper name and numbers are for later and better 4 speed O.D. trannies for the Cummins 5.9 engines.
I bought a new 1998 1/2 24 valve 5.9 Cummins powered 3/4 ton Ram 2500 with the weaker 46RH tranny in it.
I got it hot once towing my 24 Ft enclosed race car trailer with my old pump gas Duster in it in the summer in the Mojave desert and had troubles with it shifting automatically for a while after that.
I sold that truck it in 2006 and bought a new Ram 3500 4x4 for the snow up here and it has the newer better 48 RH in it, according to the mechanics at our local Dodge dealer it is a lot better than the older 46 trannies where

They are different units internally, due to torque output and case if different. Look for 90-93 units. Non lockup with overdrive. You could go 94/95 too but they are lockup. 96 on needs an electronic trans controller. You can control the lockup and od with just two switches on the 95 back.There are some other ways to do that too. You may want to get onto cumminsforum.com or look for the "turbo diesel registry" which is a dodge/cummins publication. They have a forum also.

An overdrive unit will not bolt on to a 727 case.

Diesel got either the early 727 or later the 47 or 48 RH/RE, never the 46.

Not true, the 91.5-93 auto, O/D is a non lockup 46RH derivitive. The 47RH didn't come out until 94. It was never installed in the 1st gen chassis, requires a different engine to trans adapter, starter, and relocation of the crossmember, cooler lines, shift linkage and frame clearancing for the starter to fit in the early chassis. You would also need to shorten the driveshaft as the engine to trans adapter is about 1.125" thicker for lockup converter clearance.
You may also need the crossmember from an O/D truck, I don't recall what the 89 crossmembers looked like but the mounts and the trans to mount plate is different for the O/D. You could source thie plate and maybe the crossmember from a gasser if the frame is the same height. The 94-95 V10 47RH case is the same but that is probably even harder to find but with the exception of the governor and the converter it would work.
The internals of the gasser transmissions and diesels/V10's are different and I doubt the gasser stuff would hold up behind a diesel. This would include the O/D units as well. There is a lot you can do but start with a diesel 91.5-95 or 94-95 V10 trans.

Shop around for a used Gearvendors.

Kevin

Lockups started before the overdrives, The first overdrives came out in 89 and where optional. Regardless the OP want's to "morph" a 727 and a overdrive to use in a diesel. You would have to cut the back of the transmission and weld on a section from a od trans to bolt the od unit to it. Then you have the output shaft to deal with and how are you going to activate the od?(it's electric over hydraulic) Then hope you have everything aligned perfectly. More work than just finding a od that will bolt to a diesel.

Lockup converters only available on gas versions before 94. 91.5 - 93 diesel O/Ds were all non lockup.
O/D (as well as L/U before 96) were solenoid controlled by the PCM which just grounded the solenoid(s) so simple toggle switches would work. I'm not even going to address welding the rear of a 518/46RH case to a 727. Could possibly be done but not worth the effort and the cooler/lube circuit ports are bigger on the diesel even over the gas 46RH which are larger than 727. The back of those transmissions are more dissimilar than they outwardly appear.

Depends on how resourceful you are.

Yeah, that's not a 518 O/D unit. What is that anyway?

Even though you spelled "Cummins" wrong, you are correct.

If you have the 3.08's in that thing, an overdrive is going to really up your fuel mileage. The Parents had a new '90 with 3.08's/727 and that thing did 16 mpg no problem. WIth overdrive it would have easily done 20+.

What Dodge was thinking when they run a Diesel engine at 2300 rpm I will never know. Almost as bad as them putting 3.73's in the 3rd Gens. And then sent leaflets through the Cummins Shops stating "RUN HARD" with a picture of tach needle going past 2000 rpm to "get the best fuel economy". Good thing their Customer base was clueless about what rpm a diesel should run at, and they fell for it. Then added MORE fuel with the common-rail..............FFS's............great idea, Dummies.

1964Polara: what kind of fuel mileage are you getting right now? US gals?

care to share info on that conversion ?
looks like the tailshaft housing was cut and an adapter welded to it, then a 1950ish-60ish OD from a 3 speed was added, possibly saginaw or borg-warner ?

Looks like a Borg Warner off a Lincoln Zephyr.

I have built a pile of these transmissions, if I was building one for my own 727 cummins truck and had to go out and buy stuff and only the best I would get a 48RE diesel core, any gas 46RH core, put all the 48RE guts (rebuilt) in the 48RE front case, the OD clutches, planataries and such into the 46RH OD housing, output shaft and governor with a set of diesel governor weights. Drill the rear support of the 48RE to get a nice tight fit of the governor fluid tubes thru it. Use the 46RH VB, drill out the 1-2 and 2-3 feed holes in the VB plate, turn up the line pressure a couple turns. You will need a little sleeve thingy available at most tranny supply places to fit the smaller LU-OD plug in the bigger RE case hole. Probably missing some details but this would cover the main things. I would want to keep the LU... the non LU trans would run significantly hotter and get worse MPG with all the slipping in the converter from the high TQ especially if combined with high gears, OD and towing.

Borg-Warner R11 unit from behind a T-85 3-speed, brainchild of a guy in Seattle who sold plans for the conversion. Cut off tail welded to a plate and the output shaft cut and re-splined.

48RH?? 46RH was gas, 47RH was diesel
Your 98 had a 47RE in in.... crap torque converter was the black eye in that era.
Your 2006 has a 48RE trans.... mother took some hints from the aftermarket and our trans repairs dropped dramatically after their inception.

thanks john !

I have rebuilt thousands of those RE RH 904 727... and never saw just a bad converter, the only bad converters were when something else took a major dump first like gears or clutches. The biggest cause of failures in the gears and clutches were caused by people running with cooler line or pan gasket leaks and a lack of maintenance, people hardly ever change the fluid and filter and even far less would ever get a band adjusted, that maintenance went a long ways if done properly. Most tranny shops seem to want to just condemn the entire trans and sell a rebuild than adjust a band witch I fixed many supposedly bad transmissions with no reverse or second just by adjusting the band.

Converters go bad, fill the pan with metal, clog the cooler and create a huge amount of carnage.