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The mythical CUCV 4L80E swap

MidnightDuramax

MidnightDuramax

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I have done a 4L80 2 wheel to 4 wheel conversion and also bought no specific tools. It was about 8 years ago so not sure on the specs you are looking for. The one thing I do remember is that there is a plug between the case and tailshaft housing. On a 2 wheel drive there is a pin hole in it to allow trans fluid to lube the tail shaft. When doing a 4 wheel conversion it needs to be changed to one with no hole or the trans will fill the t-case with trans fluid.
 
brazengoat06

brazengoat06

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Tulsa, OK
MidnightDuramax said:
I have done a 4L80 2 wheel to 4 wheel conversion and also bought no specific tools. It was about 8 years ago so not sure on the specs you are looking for. The one thing I do remember is that there is a plug between the case and tailshaft housing. On a 2 wheel drive there is a pin hole in it to allow trans fluid to lube the tail shaft. When doing a 4 wheel conversion it needs to be changed to one with no hole or the trans will fill the t-case with trans fluid.
Click to expand...
I'm looking for the specs on what length of output shaft to use for the conversion.

I do see the hole your referring to, it's a plug in the transmission case. Is there a different plug that I need to attain?
 
86m1028

86m1028

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Murphy TEXAS
brazengoat06 said:
I'm looking for the specs on what length of output shaft to use for the conversion.

I do see the hole your referring to, it's a plug in the transmission case. Is there a different plug that I need to attain?
Click to expand...
You can get the plug at any transmission shop.

Specs are gonna vary, there are a few different ways to do it.

I used a 2wd 4l80, tall 400 to 205 adapter (fig 8).
I had adapter machined, changed the plug & cut down the output shaft of the 4L80.

I also have the rare (91 only) factory 4l80/205 setup but decided to use the newer 2wd 4l80 because of the improved cooling & updates.

If I remember correctly I cut 1/2 to 3/4 inch off the 2wd shaft.
 
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icer97

icer97

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NE MO
brazengoat06 I am also doing the swap as we speak in my cucv and also have a 2wd 4l80e transmission. My output shaft is the 6.5in fully splined so I plan to cut my shaft down to length rather then tearing it down to replace it with a 4x4 output shaft. I plan to run my 208 and see about having the 400 to np208 adapter milled to bolt up the the 4l80. If this is a big deal as I have heard the mounting feet may contact the 4l80 pan, I found the part number for the gm 4l80 adapter that's around $60 from gm.
 
brazengoat06

brazengoat06

Member
362
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Location
Tulsa, OK
86m1028 said:
You can get the plug at any transmission shop.

Specs are gonna vary, there are a few different ways to do it.

I used a 2wd 4l80, tall 400 to 205 adapter (fig 8).
I had adapter machined, changed the plug & cut down the output shaft of the 4L80.

I also have the rare (91 only) factory 4l80/205 setup but decided to use the newer 2wd 4l80 because of the improved cooling & updates.

If I remember correctly I cut 1/2 to 3/4 inch off the 2wd shaft.
Click to expand...


I got the transmission and transfer case mated to confirm that to do a 2wd-4wd 4L80 conversion you will need the 2 5/8 adapter housing and the 3 3/4 output shaft. Now as for Plugging the orifice in the rear of the case, i have been unable to locate a transmission parts supplier that can find this part. It seems that it is not servicable. However looking at my case I see a very large drain back below the orifice that should be more than plenty to drain whatever comes out of that hole. I saw that you said that it filled up your Transfer case? That confuses me because between the drain, the input shaft seal, and how tiny that orifice is, im not sure how that happened. Im not trying to sound like im questioning you but more so trying to understand how it happened. Thanks
 
MidnightDuramax

MidnightDuramax

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Sandyston, NJ
It didnt happen. Whent to my local trans shop to pick up the parts to do a rebuild and conversion he told me about the plug. He was the one that said it would cause problems and fill the case if not changed out and had the plug to give me. Like I said it was 8 years ago and I have trouble remembering what I did at the begining of the week so can't really remember where it was located or how it would cause a problem. All i do remember is him telling me this and having the replacement part for it.
 
rustystud

rustystud

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Woodinville, Washington
brazengoat06 said:
Lol or you can pressure check it before you reassemble the transmission. Are you done yet?
Click to expand...
I'm curious brazengoat. How many automatic transmissions have you rebuilt ? If you have built more then one then you would realize that the seals can be damaged from a faulty install and still pass a air pressure check on the bench. It's after it has been run awhile that the damaged seal will let go.
 
icer97

icer97

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NE MO
I had a guy on another forum that's done the 2wd to 4wd conversion tell me to make sure to plug the drain hole in the rear housing also. He said he popped out the plug with the hole and took it up to the local parts store and sized it up to some freeze plugs until he found one close to size to drive in place to block the oil passage. According to him not only do you have to worry about oil passing back and forth but a loss in line pressure due to it also.
 
brazengoat06

brazengoat06

Member
362
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16
Location
Tulsa, OK
rustystud said:
I'm curious brazengoat. How many automatic transmissions have you rebuilt ? If you have built more then one then you would realize that the seals can be damaged from a faulty install and still pass a air pressure check on the bench. It's after it has been run awhile that the damaged seal will let go.
Click to expand...
Enough of them.

MOST 99% seals that pass an air check on reassembly will last the life of the transmission. I find it funny you haven't even bothered to ask what method I'm using to install the seals yet would rather argue. The method I use is just as reliable as an installer but your more than welcome to do it the more expensive way.
 
brazengoat06

brazengoat06

Member
362
2
16
Location
Tulsa, OK
icer97 said:
I had a guy on another forum that's done the 2wd to 4wd conversion tell me to make sure to plug the drain hole in the rear housing also. He said he popped out the plug with the hole and took it up to the local parts store and sized it up to some freeze plugs until he found one close to size to drive in place to block the oil passage. According to him not only do you have to worry about oil passing back and forth but a loss in line pressure due to it also.
Click to expand...
Yes seems like I just read a similar thread last night. Not sure how true it is but it's definitely plausible depending on the oil passage that it's tied to, so I am gonna try and do the same and find a freeze plug.
 
rustystud

rustystud

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Woodinville, Washington
brazengoat06 said:
Enough of them.

MOST 99% seals that pass an air check on reassembly will last the life of the transmission. I find it funny you haven't even bothered to ask what method I'm using to install the seals yet would rather argue. The method I use is just as reliable as an installer but your more than welcome to do it the more expensive way.
Click to expand...
Well then give use some pictures and a statement of how it's done. You have me curious now. Actually I'm all in favor of a good and cheap way of doing things so long as it really works reliably .
Though I do question your 99% . I have found out doing tranny rebuilding now for 40 years that the actual number is more like 80%. Doing air-pressure checks is just some added insurance of a good rebuild, not a guarantee.
 
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