Tranny swap question

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Maaac1789

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Hey guys, this is technically a tranny question, but since it's related to an LS swap, I decided to post it here. I did an LS 5.3 swap on my daughters 83 K10 last year, and used the 700r4 that came with the truck. I had it built, but it has shot its load already, so I am considering putting a 4L80E in the truck. I am looking for guidance on what all I will have to change, besides the obvious harness issue. My computer will run the tranny, I was just wondering about linkage, and crossmember mods that might be necessary. Also, I bought a Dakota Digital, pass through VSS for my swap and used the cable speedo. Will that work for the 4L80? Thanks for any guidance.
 

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just going off memory here, sorry if I'm wrong. I think you'll have to shift the crossmember back one bolt and drill new holes for the back set....don't hold me to it though lol.

What I do know is you'll have to change the input spline on the transfer case and you'll need the applicable adapter between the trans/transfer case. Not sure if a TH400 is the same pattern or not. Just a thought.

not sure off hand on the difference in length of the 2 trans. Could require drive shaft modifications.

I believe the vss setup you have will work as it did with the 4l60.

Curious what transfer case and what axle ratio's?

I'll try to help dig up some info on it. You might try K10 4l80 search here in the forums. Also google 4l80 (transfer case #). I'm sure others will chime in pretty quick.
 

Maaac1789

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I'm using the np208 that came with the truck and 3:73 gears. I'm running 35s on it also
 

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After a bit of research, I'm thinking the most cost effective option would be a 4l60e swap. It will take a lot less modification.
 

bucket

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After a bit of research, I'm thinking the most cost effective option would be a 4l60e swap. It will take a lot less modification.

The 4L60e is very comparable in strength to the 700r4. A properly built 700 should have lasted much longer than that.
 

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Either something was off on the 700r4 or it was used hard. 4l80e will need a different adapter and input shaft swap on the 208. 4l60e is not much difference unless you were using older than 87 700r4
 

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I'm not sure what year the 700r4 was. It does have a 30 spline input shaft, so I'm pretty sure it is newer than what came in the truck.
 

Maaac1789

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I was shying away from the 4L80 because of it moving my t case back and necessitating driveshaft mods, but, I just realized, I have adjustable motor mounts. I wonder if I could kinda keep my t case in the same location and just shift the engine forward a bit?? Any thoughts?
 

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How's the clearance in the engine/cross member area up front? Are they going to meet if you slide it forward, or is there room?
 

Maaac1789

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I already had the engine mounted one bolt hole forward, then moved it back, so I know it will fit. I notched the crossmember slightly to clear the corner of the oil pan.
 

bucket

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I was shying away from the 4L80 because of it moving my t case back and necessitating driveshaft mods, but, I just realized, I have adjustable motor mounts. I wonder if I could kinda keep my t case in the same location and just shift the engine forward a bit?? Any thoughts?

The added expense of the driveshaft modifications is well worth it compared to another failed transmission swap in a year or so.

A common 4L80e/241 adapter will work as well as a th400/208 adapter. Either one of those are likely to come with the 4L80e or 32 spline np208 you would be looking for.
 

Camar068

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The added expense of the driveshaft modifications is well worth it compared to another failed transmission swap in a year or so.

A common 4L80e/241 adapter will work as well as a th400/208 adapter. Either one of those are likely to come with the 4L80e or 32 spline np208 you would be looking for.

Thx bucket. I knew there were cheaper adapter options out there....been a while. Also, the crossmember relocation came from the "6l80 swap" memory bank I think.
 

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Thx bucket. I knew there were cheaper adapter options out there....been a while. Also, the crossmember relocation came from the "6l80 swap" memory bank I think.

I don't know the length differences between the two adapters and the 80e. Crossmember relocation wouldn't surprise me.
 

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Badly adjusted TV cables usually murder the 700R4 and I have yet to see one last behind the LS motor without the use of the Bowtie Overdrives adapter (and even that often does not guarantee a proper adjustment). People thing they can eyeball the bracket, but the geometry of the bracket on the TBI and Carb setups has some variance in it at different throttle points that I do not think is properly emulated by all the home brew experts. That being said, if you have access to a 4l80e I would go that route because its just a much stronger transmission and a stock rebuilt 4l80e should outlast a 4l60e by a long shot. You will have to move the cross-member back, shorten the rear driveshaft, and lengthen the front driveshaft. Likewise you will need to make sure you get a 4l80e adapter and either a NP208 that was behind a th400 or take your current one apart and swap in a 32 spline input shaft on your transfer case. After that you do a pin swap in the wiring harness for the 4l80e connector and have your tuner update your tune for the 4l80e (do the segment swap and adjust the shift points). I would recommend going on ahead and having a rear aluminum driveshaft made as well. There is a reason most all the new LS trucks have them, especially the 4x4 trucks with taller gears. The forces involved kind of dictate it.

Likewise you can take a chance with the 4l60e. There were incremental improvements on it beyond what is offered in the 700r4 and those changes make it a better trans overall. the computer also does a much better job of managing pressures and shift points than the manual TV cable ever did on the 700R4.

One thing that will also help, if you have not made this change yet, is bypassing the trans cooler in the radiator and just mounting an independent cooler. A lot of folks never think about it, but running it through the radiator essentially guarantees that your trans fluid will never be less than 170 to 190 degrees as it enters, because that is static temp of the water as it circulates. Moving it out of the radiator will allow it to cool as low as possible and heat is the enemy of any automatic transmission.
 

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