Well, in researching the NV4500 parts, I have discovered something I wasn't quite expecting. It seems the early Cummins auto trans engine plate is different than the one used for a manual trans, and was later used for all trans, whether auto or manual. So, it looks like I will be needing a different rear engine plate.
On a brighter note, it seems the 5th gear issue may not be much of a concern. The original gear wasn't fully splined, and this was the primary reason the nut wolud back off. The newer gears are fully splined, so the portion that is forward of the splines on the shaft actually allow the inside of the splines to ride on the shaft. My 5th gear is the fully splined gear.
The non-fully splined gears has clearance between the inside of the gear and the shaft, as the shaft diameter was the same as the inside (bottom) of the splines. This allowed the gear to deflect under a hard pull, thereby causing the nut to work loose. The fully splined gear prevents the deflection, since the splines ride on the smooth part of the shaft.

The updated shaft is fully splined as well, but also uses a 3 piece thrust washer that requires an additional groove to be machined into the shaft. It's claimed that this groove weakens the shaft.
Honestly, I doubt either would ever be an issue in this application, but chances are I might forego the updated output shaft, and use those funds to acquire the *correct* rear engine plate that I didn't even know I needed........

Bearing and syncro kit, probably a good idea though.......

 

After further investigation, I have concluded there is no need to dive any deeper into this trans. Seems I got a good unit, for about the going rate of a core.
I spent a little time cleaning the tailshaft housing today. Will reinstall it, (after buying/installing a new 5th gear nut) and then leave the trans standing on the face of the bell housing, while I soak it with degreaser and then spray it down with the power washer. That *should* reduce the chances of getting any water inside the trans. Will have to put the speed sensor back in, for now. Need to locate a speedo drive adapter for an older Mopar, back when they still used a real (cable driven) speedo.........

 

I am thinking the 92 donor was cable drive, not real sure.

 

I believe they went VSS electric speedo in 94. However, the older cable driven adaptor is a perfect fit in the 94-97 NV4500. 98+ they dropped the VSS in the trans, and went to using the VSS in the rear diff to feed the e. speedo.
I got a 97 trans, for the speedo drive ability. I would like to have a 99+ top though, since they have a removable shift tower that leaves the top of the trans flat when removed. Makes it a bit easier to get in/out of place, compared to the 94-98 style. At least the stick comes out, only leaving about 2" high tower to deal with......

Also, I think I have found a guy local that has the needed rear engine plate. I'm hoping to get started with prepping the engine to mate to the trans, within the next couple weeks. My plan is to have the engine and trans fully prepped for installation prior to touching the truck's current engine/trans.
Of course, I still haven't located any pedals for the hydraulic clutch yet.

 

I've got an interesting option on my hands. The guy with that 1M+ 24V dodge brought it in today for the planned upgrade to a South Bend dual disc clutch. His truck has the NV5600 6 speed, so it uses a 13" clutch and 1.375" input shaft. The NV4500 uses a 12.25" clutch and 1.25" input shaft. But, the flywheel and 13" clutch kit can be used in an NV4500 by installing an aftermarket "upgrade" 1.375: input shaft kit that costs around $200.
I don't have a flywheel or clutch, yet. I could always use these since they are in great condition, but I'd have to buy the input shaft kit. Thing is, the current input shaft is buggered up a bit, and really *should* be replaced anyways. The stock 1.25" input shaft and bearing/seal costs about $100, then I'd have to buy at least a clutch kit (flywheel is dual drilled), which would make it cost more to go back with "stock" parts, compared to the heavier duty 13" setup. And, this particular 13" clutch is the heavier duty "upgrade" steel backed disc for the 6 speed....... ($300 retail)

I know, everyone frowns on installing a used clutch. But, we just installed it in that truck 6-8 weeks back, and the truck spent 2 of those weeks sitting at the shop waiting for a replacement trans to arrive, after the old one literally exploded and caught fire....... Was no repairing it, since the output shaft is no longer available, and the slip yoke had welded itself to the broke-off rear portion......
We just replaced the trans a couple weeks back. Dunno why he waited till now to have us do the clutch install, would have been real easy to do it while the trans was already out...........

Yes, it is MASSIVE overkill for a "1/2 ton" truck, just like the 6BT and NV4500 are......
Besides, I'd rather see them get used, than go in the scrap bin.

 

Just do it.
"Free" parts are a great thing if you know they haven't been abused.

Just how does one blow up and catch fire to a 5600?
How does the yoke get "welded on"?
Maybe needs some Honda Moly60 paste on the splines before it gets locked down?

 

He hauls cars (3 at a time) on a ~55' wedge trailer.
It wasn't a bolt on yoke, it was a slip yoke. Dunno for sure it was "welded" together, or if the shaft broke inside the yoke, locking it in place. An 8lb sledge wouldn't budge it, so we used the hot wrench, it'll get anything loose....... Or at least part of it.
This guy spends quite a bit of money in our shop. Prolly over $20K already this year alone. Then again, 2 NV5600 trans and a new 24V Cummins aren't exactly cheap, even without the cost of labor........


As for abuse, they look great. We already knew that, since we had them off when the trans was being replaced. The pilot bearing went bad, not sure if it was damaged from the trans failure, or just happened to occur at the same time.
Flywheel is smooth. You can see where the disc has been contacting it, but cannot feel it. We inspected it thoroughly when the trans was replaced, and saw no reason to change it. 10 days later, it still looks just as good........
I see no reason I shouldn't just go ahead and spend a bit more for the bigger input shaft, and use these "discarded" parts. Especially considering I was about to order a clutch kit/flywheel combo anyways, along with a new input shaft. I can use those funds for a rear engine plate and bigger input shaft.......

 

That's a no-brainier to me. But then, I'm the one installing a 500+ ft-lbs 400 in a 1/2 ton truck. So I'd say do it.

 

I intend to.
I don't think the 6BT is gonna have quite that much torque. 400 lb/ft is stock rating. Guess I'll just have to make do with a bit less torque, and twice the MPG....... I'm still debating whether to try the 2.75 rear axle, or swap to the 3.25. Not sure which will give better results.
I will be turning up the wastegate though. I won't be having to keep it de-tuned since I won't be running that crappy auto trans the engine was originally mated to......

 

I think I'd try the 2.75 and change if needed.

 

What's redline on a 6BT?

2.75's seem tall, but it's only a F150.
400 foot pounds seems a lot compared to the 225 your 300 made.
I think acceleration would be a big step up.

 

Both engines have boat-loads of torque from idle up to 3 grand. You have a low 1st and 2nd gear, so even 2.75's shouldn't be an issue. I'd give it a try before changing the diff.

 

Governed speed is 2700 stock. After market springs can allow it to twist to 4K, or more.
Peak torque on the 6BT starts around 1400, and tops out at 1600. 2.75 gears, with the .73 OD, will put my cruise (65) RPM in the mid 1400's (1440) with 2.75 (2.01 final), or right at 1700 with a 3.25 (2.37 final).
I'm thinking the 2.75 might give slightly better highway MPG, at the cost of having to wind 4th up to speed, then select OD, and make a 55 MPH zone almost too slow for OD (~1200). Sure, the engine can pull at that RPM, but will it actually hurt MPG by asking it to do so? It takes a bit more fuel to spin the turbo at lower engine RPM than it does at higher RPM. And, lets face it, the more air the turbo can push in with the lowest amount of fuel, is what's going to net the best economy. Black smoke is lost power, and wasted fuel, but a certain amount is required to get the turbo spun up enough to push the air better.
I also want to be able to still do some towing with the truck. The 300 could handle it with the 2.75 gears, but it had no OD and a non-locking convertor to assist in the process......

One last item to consider. I can get a speedo gear to calibrate the speedo with a 3.25, but I don't think they make one with few enough teeth to get it close with a 2.75. The fewest teeth gear they list, will match up pretty decent with a ~3.08 and 31" tall tires. They go up from there, to the point of being able to use 5.13 gears with as small as 33" tires........
I have been running 31" tires on the rear for a while, and want to continue doing so. They have much better stability under a load than even a LT235, mostly due to thicker sidewalls.
Speedo gear info: Jeep/Dodge Speedo Gears

 

I think there is a way to calibrate the speedo, so if you can get it there with a 3.08 then you might be able to dial the 2.75's in. But the speedo may be one of the last things to tune.

As for MPG, the 2.75's should give the best but may require shifting a bit more. The diesel will continue to pull at lower R's, but acceleration won't be much until you get enough speed to spool the turbo up. Judging by the sound of my wife's GLK's engine and the MPG we get, bringing in the turbo hurts the economy significantly.

 

It's not "bringing in the turbo" that hurts economy, it's bringing it in too much.
I want the engine to be *capable* of making ~30 PSI, but my driving style will likely not see over 10 PSI very often.

Newer diesels have variable turbos, so they can spool up much quicker at lower RPM, then change the angle of attack as the RPM goes up to prevent over speed in the turbo. This yields better MPG and lower emissions, along with far better low end power/torque. Over using the additional boost capabilities will result in more fuel getting burned. Learning to get the turbo spooled up, then easing back on the throttle, can result in much improved MPG, without much loss in acceleration. This is not an easy thing to do, as it is rather unnatural to those who have driven gas burners for many years.