M1031 - 4L80E conversion ??s

[cjtroutt]

The NP203 is used for only an range box in between Th 400 NP 205 the gear set in range box is revers around to make an DR & OD system An good Tshop can do mods. or google it.

 

[jimmy-90]

I was curious about the NP203 overdrive myself. I googled reverse NP203 overdrive and was able to find an article about someone who used this reversed 203/205 setup on his blazer. The article says that useing that set up will cut your gear ratio in half which would be to high for a cucv. I guess it's possible to use something like that if you have a 6BTwinTurbo and can handle your M1008 at like 200mph lol. Anyhow the guy in the article with the blazer and the reversed NP203 was able to half his gear ratio because he was running unimog axles with 7something gears and wanted to be able to drive up the street with it. The article said that he had a place called OTT Industries build it for him.

 

[Crash_AF]

Well, the OD would be .5, which is a little taller than the usual .63 or .7 overdrive ratios, but with a 4.56 geared 1008 on stock 235/85R16 tires, in OD you would be pulling 1750 RPM at 70 MPH. Unfortunately I don't think you can shift the OD box in while moving, which means your acceleration would be slow up to highway speed, but once there, it would significantly drop your RPM from 3500 RPM with the stock setup.

I'd be interested in seeing how well the engine handled 75MPH at 1800RPM.

Later,
Joe

 

[jimmy-90]

Went back and found the link to that article about that blazer with the NP203 overdrive. Here it is. BC4x4.COM four wheel drive, 4x4, offroad and fourwheeling site. This guy's truck is very interesting.

 

[cjtroutt]

Well I run this setup & 6.2 L TH 400 Np203 NP 205 t case my truck runs just fine with this setup your 4.56 gear set will act like
you have an set of 3.07 the M1009 has 3.08 in it the tires are not much differnt in rev per mile.
In stead 55 mph & rpm through the roof rpm 1800 or so APROX.
I changed my rear axle last month to Dana 70HD with An 3.07 gear & sold my TH 475 NP203 NP 205 T case that my frend was in
need for his truck that he did an axle swap out DUCE to his M1008 & his gear set 6.17. he only going to run 385 65R22.5 tires
off an semi truck.

 

[Keith_J]

Interesting thread. Since I am pretty handy, retrofitting a 2WD 4L80e to 4x4 seems like an easier proposition .. I would think having the TOSS at the transmission instead of the transfer case would be better off road. And DEFINITELY for operation of the PTO. Having the torque converter locked up would mean much easier engine control off the generator governor. Currently, there is an overspeed protection system and a ramp signal generator to compensate, these would be unnecessary with a locked up torque converter.

There are scads of 2WD transmissions out there. If all I need to do is have 35 thousandths machined off the existing transfer case/ transmission adapter, that is an easy thing.

Also, I intend to move the engine forward 1-1/2" to compensate for the increased length, meaning no driveshaft work. The 1031 has three driveshafts plus the TC neutral safety switch. Also no modifications to the shifting mechanisms. Looks like some modifications to the oil pan but these can be done without removal.

Edited to add: The stock TH400-NP205 8-bolt will work fine with the above modification, getting the 2WD version of the 4L80e will have the tailshaft housing to use as an example for machining. The 4L80e will need to have the full spline length and 6" stickout with tailshaft housing removed, some of the tailshaft will need to be removed. And I will need to research the tachometer input signal, think it is a 40 tooth per revolution Hall Effect sensor.

So for a few dollars to get the adapter machined, it looks like a go. Note again, this is a stock M1031 with NP205 figure 8 bolt pattern transfer case.

Yes, there will be an electronic control system. But it already has an electronic governor for the generator.

 

[detroitmuscle1986]

So, I have a complete running 98 gmc 3500 with a 6.5/4l80e combo. I want to swap that combo into my 1028A1. From what I have read I believe if I machine the adaptor between the tranny and TC I can make the 4l80 fit the np205. Where I get lost is with the electronics part of the swap. I will keep the stock electronics on the 6.5 and use what I can off of the donor truck. Will I need to make a custom speed sensor to work on the 205? Can I use the electronic throttle position sensor from the donor truck? What other electronics will I need to use or buy when I make the swap?