M1031 - 4L80E conversion ??s

truck0590

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Alright, I've lurked on here before, but never posted up. So I finally joined and figured ya'll were the most likely to have an answer.

Background: I have an 86 M1031 with utility box on the back. It has a 12KW generator run from the the PTO on the 205 tcase. Everything is currently stock. Having trouble with my TH400 tranny and instead of fixing it I would like to 'upgrade' to overdrive to give the 4.56 gears more highway manners.

I need to know what needs to be done to swap the 4l80 into my truck. I have a line on a 2WD 4L80 behind a non-turbo 6.5. I can get the whole thing and all the computer and harness if required. What do I need to do to make this work?

Any and all help is much appreciated.

Truck
 
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mangus580

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RE: 4L80E conversion ??s

What year is the 6.5? The problem with the 4L80 is the computer controls. If the 6.5 is 94 or newer, the IP is run by the computer too, and you probably wont be able to use it.
 

motorolanut

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The 400 is one if not the best auto trannys used by GM..You would be better off changing gears in the front and rear pumkins to 355 or 373....have the 400 rebuilt and swap em...Just my 2 cents worth....Anybody else wanna chime in here??
 

Westech

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Well I have a 700r4 that I want to put in my 08.. see the over drive trans have lower first gears then the th400 and a overdrive to boot. like .71 ish to one. A extra gear would really help and the lower first would be nice when towing of loaded. I would go with a good rebuilt 700r4 (non computer controled) and you can get all the parts from B&M to have the lock up and kick down all working great.

only thing is you will have to get a new t-case too. the 400 case will not bult up to a 350 or 700. shaft size is different.
 

mangus580

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motorolanut said:
The 400 is one if not the best auto trannys used by GM..You would be better off changing gears in the front and rear pumkins to 355 or 373....have the 400 rebuilt and swap em...Just my 2 cents worth....Anybody else wanna chime in here??
Remember, the 4L80 is the Overdrive version of the TH400... just as strong, just as tough. If I had a chance to use a 4L80, I would jump on it.
 

truck0590

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Westech said:
only thing is you will have to get a new t-case too. the 400 case will not bult up to a 350 or 700. shaft size is different.
I have to use my 205 due to the PTO required for the generator.

So nobody has done this?

Truck
 

mangus580

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There was one guy who was starting the project. You might try looking up one of the chevy forums, as I am sure someone has done this. You might even try www.dieselplace.com Its a direct bolt in swap.... its just the computer wiring thats the tough part.
 

Recovry4x4

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If you elect to use a 700R4, you wil need the adapter that was used between the 350 turbo and the 205 case. This started use in 1970 and there are still bunches out there. Be careful about the lower mount, seen lots of them broken and welded. Controlling the 4L80E is not a problem but you will have to buy a computer to do it. Last I checked they were about $800. Not sure what adapter or output shaft you would use with the 4L80E. Advance Adapters probably has that info. 4L80E is as durable as the 400. I've got one in a 6700# crewcab and it has 200,000 miles and a few thousand pulling deuces. Good tranny!
 

carguy455

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I've got a 95 chevy 3/4 ton 4x4 that was a diesel and was converted to a 350 gas, unfortunately they left the diesel 4L80E in it, they did "something" to the wireing to make it shift, but the RPM ranges are all wrong, has no power....thing is tuff as all get out though, I kicked the snot out of it for over a year and it laughed at me. I'm am in the market for the "correct" 4L80E to replace the diesel unit with [ and a fresh shortblock ]...anyone need a diesel one ?
 

ElkyRacer

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If you have a TH400 in it now, the splines are the same. Ill look at work tomorow at the diffrences in the adaptors. There are a few companies that make manual valvebodys for the 4L80s, you would just have to shift it on your own. They were around 300 bucks, much cheaper than a standalone computer for it.
 

truck0590

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If I understand the folks I would be buying from the computer is a stand alone for the tranny. It is a 6.5 4L80e out of a Frito Lay truck. If this makes a difference.
If the the 4l80 is 32 spline and will bolt up to the round pattern 205 what would I need to change from the 2wd version.

Any other help you can provide would be great.

Truck
 

Ambulancechser

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so...i'm not mental...

glad to know somebody out there wants to do the swap besides me.i've just started mine,and i'm pleased to report that the trans and x-case are in,and the rear crossmember/trans support just got bolted in this afternoon.i'll post pictures as soon as possible,likely this weekend,as work is starting it's usual spring hassel.

things to consider...my project is finally coming together after nearly a year and a half of parts gathering and research.no small task considering the parts that have been cluttering my employers shop for some time,and the effort to find them.
to start...you'll need a place to work.consider carefully,as the truck WILL be idle for longer than you plan.gather all your parts first and keep them together and labeled.

once you start,DON'T STOP...that sounds easy but it's not.you will be wondering what youve gotten into,and you will almost certainly pound your head on the wall when you forget something obvious (personnal experience).that said,on to the good stuff...

the 4l-80 is a direct bolt in to the 6.2.The 400 flex plate is a direct bolt to a 4l-80 pattern,so no flex plate or starter mods.everything fits but there are some minor issues...
the trans is about 2 inches longer than the 400;the x-case will move back that aproximate distance,so modified drive shafts will be required.
you'll need a trans dipstick from a 91' k-30 with a 6.2 and a 4l-80,only made for 1 year...very hard to find used.you'll need new trans coolant lines.(i'm fabbing mine now).you need the 4l-80 inspection cover as well...be prepared to do some trimming to fit.the bolt pattern at the back of the 4l-80 is identical to the thm-400...HOWEVER,the 4l has an indexing ring that interferes with the older adapter.if you have the older figure "8" adapter,get the adapter machined to match...not to hard,DEPENDING ON THE TRANS YOU CHOOSE.
if you choose to modify a 2-wd trans like i did,give the tailshaft housing to your machinist,and tell him/her to make the adapter the same.OR,if you can find a round bolt pattern 205,a 4wd 4l-80,and the near mythical 91 4l-80 adapter,your in business.the out put shafts are the same diam and spline count.

this is important...the output shaft on the 4l-80 has to be the correct length for whatever adapter you choose...for example,the old figure 8 needs the shaft to stickout approx 4 1/2 inches to mesh properly with the x-case.if you need to do a shaft switch THE ENTIRE TRANS MUST BE DISSASEMBLED.all out put shafts on domestic cases load from the front.the out put shafts are first in,last out.
the factory crossmember should be usable...just drill new mounting holes and your in business.(use new mount/bushings).

electronics are another big issue.i'm using a compushift controller...pricey but highly adaptable,and allows some tuning...no laptop or tach required.i haven't gotten this far yet...the stumbling block will be the throttle position sensor.getting it to work on the 6.2 will be fun.you may be able to find the independant controller from a 91 to 93 gm with the 4l-80 and a 6.2...but you'll need a tach and tps to go with.

if you have more q's post them.i'll try to respond and post updates.
 

truck0590

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RE: so...i

Awesome info.
If swap out the whole engine and trans (my 6.2/th400 for this 6.5/4l80) it should be easier. So I want to concentrate on adapting the 2wd 4l80 to my round pattern 1986 NP205.

If I take the tail housing off the 4l80 and use my th400 adaptor (I heard I need to machine this adaptor slightly to match, something about gasket differneces) I don't have the 4L80 in hand, so is the 2wd shaft too long? Can it just be trimmed down?

I would try and use the computer that comes with it. Concern I've heard is the TPS, since you can't put one out of the 205 getting it to shift properly.

Truck
 

CCATLETT1984

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truck0590 said:
Westech said:
only thing is you will have to get a new t-case too. the 400 case will not bult up to a 350 or 700. shaft size is different.
I have to use my 205 due to the PTO required for the generator.

So nobody has done this?

Truck
the np205 will bolt up to the 4l80e, the adapter will have to be machined a small amount, the only difference is that the indexing ring on the newer trans is slightly larger, so a little metal must be taken off of the adapter. You will need to get a 4wd trans though, or you can have the shaft swapped when you are rebuilding it.
 

CCATLETT1984

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in regards to the speed sensor, you can modify the rear housing of the 205, you pull off the speedo gear and a reluctor ring is put on, then you drill and tap the housing for the sensor to thread in and you have an electronic speed senor :)
 

Ambulancechser

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THATS THE RUB...

Thats the main difference between the 4x and 2x transmisions...the trans output speed sensor (TOSS).the 2x case has the toss on the trans(rear left).the reluctor ring is built in.the 4x case has the toss in the transfer case.swapping a reluctor ring into an np-205 proved to difficult to work out when i was parts gathering...i used what i could get hold of.Electronically,the toss in the x-case takes into account the change in gearing in low range...if you use a 2x case it's good to find electronics that can take this into acount.

if you must use a 4x case,you must find a way to reproduce the toss in some way...the trans can't shift without it.IIRC the factory computer needs toss,tiss(input speed),tps and tach.

easier(for me) to use a 2x case,as the reluctor ring is already there.problem with a 2x case is the output shaft.IIRC there are 5 different types.long and short 4x4,2wd slip yolk,2wd fixed,and long motorhome.

the long motorhome shaft is the easiest to use but the hardest to find.it's fully splined for it's entire length,and you can cut it down to whatever you need.for the figure 8 adapter,i used a 4x4 short shaft,trimmed by 1/4 inch.the round style length will depend entirely on the total length of your adapter.measure carefully,taking into account that the 32 spline input to the 205 sticks out of it's case about 2" (32 spline short input).

if you have an input thats the 32 spline long style,i believe it sticks out of the case about 4".this means you have to watch how much your shafts are going to mesh,as you can only cut down the trans output shaft so much before strength is compromised.this means you might need a spacer between your adapter and the trans,depending on the adapter length.changing outputs is expensive as you must dissasemble the trans.
 

CUCVFAN

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RE: THATS THE RUB...

I've been considering this swap for my civvy truck. Any idea what the total cost will be once you guys finish? I figured it was going to take me quite a bit of my own time and probably $2000+ in the trans/computer/misc parts/machining/labor to do it.

As was pointed out, the 4L80E/NP205 adapter was a one year only item, but a round pattern TH400 adapter can be machined to fit. You have to shorten/lengthen the drive shafts, but also the PTO drive and the shifter controls, too. Combine all of this with the fact that I just don't have the time to hunt down all of the bits and pieces anymore and I'm considering just spending a little extra and getting a Gear Vendors... Since it's a crew cab, I don't have to worry about too much drive angle change by shortening the rear shaft. Then again, I keep asking "Do I really NEED overdrive?" and the answer is always "No, but it would be nice." I just haven't decided if it's $3K worth of nice or not...:roll:

Here's another thread from BC4x4 about the swap, but I think the points brough up here echo it...
http://bb.bc4x4.com/printthread.php?s=e3dba372159221aca6d733a015585827&threadid=47430
 

CCATLETT1984

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RE: THATS THE RUB...

on the Spike Tv network, the show "extreme 4x4" did a 4l80e with a np205 on the end. they had the output shaft of the 205 machined down to fit a reluctor ring from a 700r4, then they had the rear housing fly cut and tapped to screw in the sensor. I have the episode saved on the computer, might be able to cut just the portion that would interest you guys and email it to ya.
 

Autocar

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RE: THATS THE RUB...

I think TCI transmissions makes a stand alone electronic controller for the 4l80e that you can program for shifts and it also allows calibration of the speedometer.
 
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