1986 M1031 4L80E Swap Question

[IdahoJoe]

I just bought a 1986 M1031 from Gov liquidation. I'm new to this truck, but I've had quite a few 1973-87 Chevy's in the past and even had a M1009 for a few months.

My truck has the TH400 and NP205 of course but doesn't look like it ever had a PTO or the associated governor on it. Whatever box was on it was removed before it was auctioned and replaced with a 1999-2007 GM truck box, I would guess that box and the box from this truck were swapped.

Anyhow, I have access to a 1992 4wd 4L80E from a 6.5 turbo engine that is totally mechanical (the engine is mechanical, not the trans). That truck uses a DB2 pump just like these and the ECM only controls the trans. I would like to swap in that trans and use that computer to control it. I know I will need the TPS off the 1992 pump and the wiring harness.

My confusion comes in the transmission to transfer case adapters. My research says my TH400 has a 32 spline male output shaft. My adapter will have the round TH400 pattern on the front and the figure 8 pattern on the t-case side. Will the 92 4L80E bolt up? If not, can things be modified to make it bolt up?

Thanks for any help in advance.

 

[GHall]

I believe if it's 32 spline, it will bolt up.. I just read a thread, lemme see if I can find it.

EDIT: Here it is, see what you think..

http://www.steelsoldiers.com/showthread.php?64004-The-mythical-CUCV-4L80E-swap

 

[IdahoJoe]

I just read that thread too. The only hitch is that writeup is for an NP208 and I have an NP205. He also used the newer adapter.

 

[GHall]

Gotcha.. Well, good luck on your build!

 

[wayne pick]

Northwest fabworks 4L80E to NP205 adapter. Part#AA-50-0410, $547.00. Ouch!

 

[richingalveston]

I have the 4l80e installed in my 1009 and soon the 205 will be installed, you can use that trans controler or purchase an aftermarket controler, I am using the TCI fast TCU. Even though I had issues getting a working controler, I like the controler. For the TPS you can purchase it from the autoparts store. You replace the vacuum style TPS on the side of the IP pump with an electric sensor. Your vacuum pump is no longer used, you can't remove it because the oil pump runs off the bottom of the shaft.

In order to install the figure 8 205 you will need an adaptor to adapt it to the round pattern of the 4l80e. You can get an adapter that also clocks the transfercase up or down. And yes you need to have a big bearing 32 spline female input shaft for the 4l80E to connect to the 205 which should be what you have if it was previously connected to a TH400.
The issue with it will be if it is long enough since you will need a spacer to adapt the two bolt patterns.
They make a long and short 32 spline female input shaft for the 205 so depending on the spacer used, you may have to change the shaft.

I looked at some spacers but since I did not need one I did not research it in depth.
I had a figure 8 205 tcase with 27 spline input, I had to have the input bearing hole bored to install the larger bearing. I am installing a doubler and an adaptor is not needed in my application but I did rebuild the 205 to change the input shaft and it is not difficult.

The later model 4l80e (96 and up) is supposedly the better trans case because the cooling lines are split so if you are paying a lot of money for the early model one and plan to rebuild it then you may want to get a later model core and rebuild it for the same money.

 

[Jim Hunter]

Any updates yet IdahoJoe ???

Jim

 

[jsgmdiesel]

I thought about the idea of a 4L80E until I realized what a nightmare the wiring would be, plus trying to find the right T-case adapter and for a decent price. GM switched from the figure 8 racetrack pattern to the round in '85 and also changed the crossmember from a flat one that bolted on the underside of the frame to the curved type that bolts on the topside of the bottom framerail. Also the female input shaft is about twice as long on the round style 205s to further complicate swapping. The round style 205 was only found in 1 tons 85-87 and after that only in crewcab 4x4s to 91 so not very many are around. To complicate matters even more I think all CUCVS 84-87 use the earlier 1984 crossmember and figure 8 205 transfer case. I ended up spending the $3,000 for a GV overdrive and I have no regrets. Bolt it onto the T-case, plug in the wires to the control box, $80 to shorten the driveshaft, and its on the road working flawlessly. One thing to check, if your 205 has a slip yoke you will have to change it to a fixed output shaft.

 

[IdahoJoe]

No progress yet. I'm thinking I will build the transmission to t case adapter. I haven't picked up the trans yet but once I get the TH400 and the 4L80E next to each other with their respective adapters, I can start making chips on the mill.

 

[richingalveston]

The back of the 4l80e is the same as the th400, with the exeption of the diameter of the inside of the housing. you can use the same th400 adapter on the 4l80e you just have to mill the lip on the adapter down (small lip on the adapter that fits into the trans housing). IF you were using a 208, you would be done and everything will bolt up. For a 205 you really just need to add a flat plate to the other side of the th400 adapter with the right bolt patern for the 205. you can accomplish this by purchasing a clocking ring form Trail tech fab to get the plate. It has been a while since I checked but the plate sold for around $75. and it gives you an option to clock the case up. You may still have to change the input shaft on the 205 to the long shaft or you may have to make the adapter thinner to account for the thickness of the plate. not sure on this.

 

[IdahoJoe]

I didn't understand what you meant the first time, please excuse my thick skull.

This thread on pirate gives me some ideas:

http://www.pirate4x4.com/forum/moto...ts-replaces-stock-full-spline-engagement.html

I currently have the TH400 and a figure 8 NP 205. Factory for my M1031. If I just need to knock the lip off the front of the adapter, it seems like the only other thing I need to make up for is shaft lengths of the 4L80E vs the TH400. They should both be 32 spline.

I don't understand where you say "For a 205 you really just need to add a flat plate to the other side of the th400 adapter with the right bolt patern for the 205." I already have the right pattern for the NP205 because it's the original transfer case for this truck. Were you thinking of a truck that started with an NP208?

 

[richingalveston]

sorry, I thought it was a 1008 with the 208 and that you were changing to a 205, so my bad.

yes, then you have it easy. all you have to do is mill the inside lip down on your current addapter and it will fit the 4l80e.

I have a 1009 that had the 208 and I am changing to a figure 8 - 205. with 4l80e so my addapter issues were different from yours.

 

[IdahoJoe]

Thanks! You are giving me hope that I can do this for a lot less than I was expecting. I need to get both transmissions here and next to each other. That will answer the rest of my questions.

I will have a 4L80E to NP241 (driver drop for the 1993) adapter if that would help you with your swap...

 

[richingalveston]

I think the adapter modification might be the easy part, I used an aftermarket controler and the wiring and install for this was very easy, The TPS will be needed and I believe you are going to need an engine RPM signal also. Consider a Dakota Digital DS1 module if you do need it, It is easy to install also. Use the alt signal to get RPM