M923 Transfer Case upgrade to Oshkosh 55000

simp5782

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Bummer. It sounds like the bearing locked with the output shaft. Is that what you mean or could the shaft rotate freely? From the pictures, it looks good. No sign of wear on the gears.
gears are fine. It locked up while driving at 60 with an empty trailer. I know it locked up cause it peeled the companion flange end cap back like a banana when it broke off wasnt just a thrown joint. I believe a bearing just got to hot and locked up
 

bluehorse

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clackamas, Oregon
Wow, glad you are ok and it didn't cause you to lose control or crash.

I have been thinking about doing this myself but now I'm wondering about the Hemtt transfer case and its oiling system.
 

simp5782

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I have ordered the bearings. No rush for me though. I don't use 6x6 at all and the transfer case only gives me 2mph more at 2150rpms it is only a .98 high ratio


My truck was only down about 8hrs to drop the transfer case and install the longer driveshaft from the transmission to the front tandem
 
161
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Argyle MI
I'm a little curious. After everything you've done to this truck to make it a better over the road truck. You have no use for 6 wheel drive? Why go to all the trouble? Why not just use a regular semi. You've got enough invested. Time and sweat and money. You could probably have a pretty decent semi truck that would be far more functional and comfortable. And far easier to source parts for. I'm not judging at all. I get it. As a side hobby. But you commercially use it dont you. It would make more sense as a side project to me. Just curious what drives you I guess. You've done everything I'd love to do with mine to cure it of its shortfalls. But the 6x6 is the main necessity for me. Its offroad capabilities that a normal truck could only dream of.

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simp5782

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I'm a little curious. After everything you've done to this truck to make it a better over the road truck. You have no use for 6 wheel drive? Why go to all the trouble? Why not just use a regular semi. You've got enough invested. Time and sweat and money. You could probably have a pretty decent semi truck that would be far more functional and comfortable. And far easier to source parts for. I'm not judging at all. I get it. As a side hobby. But you commercially use it dont you. It would make more sense as a side project to me. Just curious what drives you I guess. You've done everything I'd love to do with mine to cure it of its shortfalls. But the 6x6 is the main necessity for me. Its offroad capabilities that a normal truck could only dream of.

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I like using a tag trailer. I do go offroad but I don't have to use 6x6 that much. I deliver some heavy equipment offroad to remote locations but i haven't needed to use 6x6 especially with the gearing I have in the truck. It's a hobby. It is for commercial use but I don't go out all the time. Mostly whenever I need something moved back to here for myself or someone close to me. It saves us the money in the long haul. Not so much about having the 6x6 as ground clearance.

In reality between the actual truck cost (2500) and trailer cost (2200) i started out with little invested. Mostly i like the truck. and i like having a project. I am ADHD as heck.

In retrospect to the cost I have in the truck for modifications. I have $1200 invested in the CAT transmission swap as far as parts go. Transmission/Bellhousing/Cord/Flywheel/Shifter and the steel i used.

The transfer case costed me two Goodyear MVT tires for it. So less than $100. I sold the take out T1138 for $1500. and it took me $20 in steel and 6hrs to install it.

As far as the big cam swap goes. It costed me a whole $65 to do the whole engine swap as far as parts cost. I bought the M915 for $1500 condition unknown. I sold parts off of it (rear axles/radiator/fenders/cab parts/Alternator) to cover the cost of the haul back from San Antonio and to cover what I had invest in needed parts.

Wrecker springs didn't cost me a thing and i swapped them over in a day to upgrade.

Iso bed costed me $800 for it and fuel. I sold my take off bed for $600.

AC system costed me about $650 total with me making my old bracket. I sold the bracket off my NHC250 for 3x what the bracket costed me to be made for the NTC400.

Swapped a pumpkin out out on my front tandem. Costed me $100 for a whole nearly new axle and 5hrs to swap it. All and in all as far as parts go for all my mods and swaps and this and that I am under $10,000 on what i have spent total even in purchasing the truck.

Even without the 6x6 I can still climb very steep hills with a heavy load.


In the end I built it and it is how i want it. I mean its the only one of its kind in the world I am sure. If i went to something like a PB or a kenworth I would still do stuff to it like the CAT transmission. I do drive a OTR truck on occasion with a 53ft stepdeck when things need to get hauled together.

https://www.youtube.com/watch?v=6ijj1am0xv4
 
Last edited:
161
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Argyle MI
I understand for sure. I have the same ADHD itch to tinker and make things the way I want. I'm fairly certain there are no other trucks the same as mine either. I went in a different direction of functionality first though. Got tired of unloading things by hand... like to be able to haul a normal trailer too. Horsepower and powertrain durability is my next step for sure. I'm constantly testing mine offroad. I have to get in and out of the woods with firewood or sand or whatever needs to be hauled. 6x6 is a must on most of my endeavors unless it the middle of the summer. I can tell you the winch is pretty handy as well.... I've tested it a time or two. I like your route on repowering. Just not sure I want to go so far with the trans and transfercase. The air shift seems like it would become troublesome in a cold damp climate with consistent use. And the awkward driveline angles I know aren't really a huge issue. But I'd like to stay away from it if possible.

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simp5782

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I understand for sure. I have the same ADHD itch to tinker and make things the way I want. I'm fairly certain there are no other trucks the same as mine either. I went in a different direction of functionality first though. Got tired of unloading things by hand... like to be able to haul a normal trailer too. Horsepower and powertrain durability is my next step for sure. I'm constantly testing mine offroad. I have to get in and out of the woods with firewood or sand or whatever needs to be hauled. 6x6 is a must on most of my endeavors unless it the middle of the summer. I can tell you the winch is pretty handy as well.... I've tested it a time or two. I like your route on repowering. Just not sure I want to go so far with the trans and transfercase. The air shift seems like it would become troublesome in a cold damp climate with consistent use. And the awkward driveline angles I know aren't really a huge issue. But I'd like to stay away from it if possible.

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As long as you have a good air dryer. In which case I have two of them. Good clean air and normal operation it is fine. Member ponway uses his CAT 7155 in his Western Star truck and goes all over the country. He is in north central Indiana. I went with the CAT towards the small cam to see what it would do. and to tell you flat out. The NHC250, CAT 7155, T1138 transfer, and 395 tires would flat out MOVE. run 70mph turning 1800rpms. It would get up into the mid 80mph range easily. It ran great.

Nothing is comparable to the Big Cam though. I can carry a 5 ton LMTV up hill faster than it can drive on flat ground. It is nice.
 
161
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18
Location
Argyle MI
I'm leaning towards a big cam swap. I have some sleeve concerns with my nhc250 right now. Antifreeze is full of rust. I spent half a day flushing it. Made little difference. It's starting to have some white film in the over flow tank also. I really dont want a clutch pedal for sure. But I dont have the access to things as affordably as you. I know the allison wont hold the power for long either. Especially with some offroad use. I have the same concerns for the stock transfercase.

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simp5782

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I'm leaning towards a big cam swap. I have some sleeve concerns with my nhc250 right now. Antifreeze is full of rust. I spent half a day flushing it. Made little difference. It's starting to have some white film in the over flow tank also. I really dont want a clutch pedal for sure. But I dont have the access to things as affordably as you. I know the allison wont hold the power for long either. Especially with some offroad use. I have the same concerns for the stock transfercase.

Sent from my SM-G892A using Tapatalk
You could transplant the whole setup from a 915A1. With the HT754 it has. Just move your transfer case back 18inches. You can use two transfer to front tandem driveshaft from a m931 truck to put in as jackshaft and tandem shaft

You will have to raise the cab and remount everything like I did due to the SAE 1 bell housing on the big cam and that bigger allison setup
 
161
2
18
Location
Argyle MI
You could transplant the whole setup from a 915A1. With the HT754 it has. Just move your transfer case back 18inches. You can use two transfer to front tandem driveshaft from a m931 truck to put in as jackshaft and tandem shaft

You will have to raise the cab and remount everything like I did due to the SAE 1 bell housing on the big cam and that bigger allison setup
The only hiccup with that is my hoist setup for my dump. I have maybe an 1/8th inch clearance from the back of my transfer to my spool valve mount right now. I kinda shot myself in the foot for any wiggle room there.


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