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Discussion Starter · #1 ·
I undertook this swap due to limitations of the 6L80. The cost to rebuild the 6L80 with no guarantee was not inspiring, especially when I'm looking to push a good bit more power then I am now once I get the trans and fuel sorted out. I looked at 4L80's but didnt want to deal with electronics again interfering with my shifts.

My buddy Mike offered up his TH400 that last lived life in his 80's Suburban. I couldnt think of a good reason not to. I ordered an SFI flexplate, B&M shifter, and other small parts to make the swap complete.

We compared the lengths of the 6L80 and TH400 which were surprisingly close. Once the 6L80 was out of the way we mocked up the TH400. Lengths end to yoke were within a 1/4". I installed a Hughes Performance SFI Flexplate and converter spacer. Then bolted up the TH400, which all but three of the trans bolts went in. Obviously there is a slightly different bolt pattern between the trans, mainly the two oilpan bolts and the top center bolt the 6L80 uses. The existing crossmember that supports the 6L80 works for the TH400 without drilling any holes. I used an Energy Suspension TH400 mount which bolted right up to the cross-member.

I took off the 6L80 yoke adapter plate from my Driveshaft Shop driveshaft and removed the u-joint. I then installed a new 1350 u-joint to the driveshaft and a Hughes performance TH400 slip yoke to the u-joint. The driveshaft is the perfect length, carrier bearing is in the same spot. All is well there too.

Then installation of the B&M shifter. I used a piece of plate steel to block off the hole from the OEM shifter. I used existing bolt holes to secure the piece. Then bolted the shifter to the blockoff plate once I found a place that worked for my arm length. The only hole I had to drill was for the shift cable that went down to the trans. It's a 1" hole about 4" forward of the shifter. Ran the cable down to the B&M shift bracket and bolted it to the trans. Ran through the gears to make sure it was adjusted properly.

Removed the OEM trans cooler lines and installed a new trans cooler. Ran new 3/8" line from the cooler to the TH400 which worked great, took about 10 feet of line to run it cleanly.

I had to remove the TCM from the 6L80 and plug it in for the car to start. I ran the 6L80 trans harness up into the engine bay, put some heat resistant material on it where it came near the header. I notched the plastic area that holds the cabin air filter and ran the cable into this area. I connected the TCM and put it in this free space. really you cant even tell its not supposed to be there.

Car started up and runs fine, went and did some donuts for good measure to test it out. Really not a bad swap, surprised more people havent done it. Took about 7-8 hours of mechanical work taking our time, BS'ing, running to the store for stuff we forgot, looking outside at the snow, etc.. then about an hour of figuring out what the electrical system needed for the car to turn on, start, etc.

I adjusted my HPtuners tune and only have one code right now. That was only a quick look, I'm working on getting rid of the remaining code so I can be check engine light free with this swap.

Pics to come later...
 

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Sounds promising. The way some of you guys mod cars is astonishing. I would be terrified to do something like this.
 

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MGM GT is a God of the car world. It's amazing seeing him tear down an engine and trans in no time.
 

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FAN F'IN TASTIC!!!!! i love my car except for the 6L80. with the power i m putting down, this trans is terrible. and like you said, there really isnt anything you can do to make it bulletproof.

i was just talking to a friend (whos car is getting a new 6L80 put in as we speak) about this yesterday. because a 4L80 swap is not only expensive! but i hear of lots of trouble getting it to talk to the car.

my only concerns are highway rpm. have you had a chance to drive it at highway speeds???

GREAT JOB!!!
 

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Discussion Starter · #6 ·
Sounds promising. The way some of you guys mod cars is astonishing. I would be terrified to do something like this.
haha yeah I'm never concerned about taking my cars apart to change them.

MGM GT is a God of the car world. It's amazing seeing him tear down an engine and trans in no time.
Thanks... just a mere mortal though.

FAN F'IN TASTIC!!!!! i love my car except for the 6L80. with the power i m putting down, this trans is terrible. and like you said, there really isnt anything you can do to make it bulletproof.

i was just talking to a friend (whos car is getting a new 6L80 put in as we speak) about this yesterday. because a 4L80 swap is not only expensive! but i hear of lots of trouble getting it to talk to the car.

my only concerns are highway rpm. have you had a chance to drive it at highway speeds???

GREAT JOB!!!
Yes the 6L80 has been my nemesis since first owning this car. I just hate it. I got the tuning down pretty good but I hate autos to begin with and a double overdrive is just annoying. I wanted to get rid of the electronics entirely so this was a good choice for me over the 4L80, much cheaper too. Plus I have some ideas in the future this will be fun with.

I have high highway RPM's anyways since I have 3.70 rear gears, but I'm switching to a 28" tire which should help.

and no pics? for shame
Sorry I wasnt the one taking pics, my buddy should post them soon.
 

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haha yeah I'm never concerned about taking my cars apart to change them.



Thanks... just a mere mortal though.

.

HA HA, Indeed you are, but it is a joy to watch you work MGMGT. I'll be interested to Feel the Difference once you get the tune sorted.
 

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9 Second G8
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Sky, did you try the new trans type switch in the latest beta hptuners? I was hoping to not have to retain the tcm.


Sent from my DROID2
 

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If.its a manual valve body you could.switch to a manual tune
 

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Congrats!!! Nice job....

I am still trying to get the 4L80 to work without the Tehcm plugged in... trying to get it to work with the G8 ECM and a GM T42 controller... have communication issues for the last 6 months..... I may have to just give up and go the aftermarket trans controller direction but still trying to make mine all GM OEM stuff with no Tehcm plugged in.... getting close...

congrats on yours!!!
 

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Discussion Starter · #12 ·
Sky, did you try the new trans type switch in the latest beta hptuners? I was hoping to not have to retain the tcm.


Sent from my DROID2
I looked at that but wasnt sure if I should use it. It works fine with the TCM plugged in and only takes about 10 minutes to pull it out, reroute the wire, and connect it in a inconspicuous place. I may try it though just for kicks, I was going to post on the HPT forum to see if anyone tried it yet.

If.its a manual valve body you could.switch to a manual tune
You can go to a manual tune anyways since even the regular valve body gets zero input from the car, it purely a mechanical device. But the car will only start with the TCM plugged in so far.

Sky, got a part number or link to the trans mount you used please?
This mount bolts right up to the TH400 and the stock cross member:

http://www.jegs.com/i/Energy+Suspension/355/3-1108R/10002/-1

Congrats!!! Nice job....

I am still trying to get the 4L80 to work without the Tehcm plugged in... trying to get it to work with the G8 ECM and a GM T42 controller... have communication issues for the last 6 months..... I may have to just give up and go the aftermarket trans controller direction but still trying to make mine all GM OEM stuff with no Tehcm plugged in.... getting close...

congrats on yours!!!
Yeah after seeing the f-bodies have issues/frustrations with the 4L80 I wasnt about to go down that road.

Not sure if you've looked into it but [email protected] offered me a G8 GXP wiring harness and ECM if I couldnt get it to work this way. That way you could use HPtuners for your ECM and something like the TCI controller for your trans with a cleaner install.
 

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Not sure if you've looked into it but [email protected] offered me a G8 GXP wiring harness and ECM if I couldnt get it to work this way. That way you could use HPtuners for your ECM and something like the TCI controller for your trans with a cleaner install.
Yea We have a TCI controller but decided to go GM OEM stuff to see if we could make it work..... much more complicated..... but maybe worth it in the end.... and the Tehcm needs to be in the car no matter which harness you use or how you wire it... the camaro guys can get away with it but not us.... I have already tried the GXP setup and still needs tehcm plugged in.... (or we just messed up :) )....

I think we can redo the cals and software so the ECM controls the T42 just like they had in the Gvans (with 4L80's in them.._).... just getting there is a pain.... my car has been ready since August except for this damn controls software issue messing me up... the TCI way I would have ran it this last fall..... but oh well... trying something a bit different... I am jealous you got yours done already... but I am lazy when it comes to shifting.... thats why I didnt go the 400 route....

ps.... what is this about boost in you signature.... you got something going also on that?..... :wall:
 

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Discussion Starter · #15 ·
Thanks Sky. Got the mount on order.

If you try the manual switch before I do, please let me know if it works!
Sure thing, the TH400 lines up like the G8 is its home. Like I said the only hole you have to drill is for the shift cable but you have to remove the center console and HVAC vents to get a place to do it.


Yea We have a TCI controller but decided to go GM OEM stuff to see if we could make it work..... much more complicated..... but maybe worth it in the end.... and the Tehcm needs to be in the car no matter which harness you use or how you wire it... the camaro guys can get away with it but not us.... I have already tried the GXP setup and still needs tehcm plugged in.... (or we just messed up :) )....

I think we can redo the cals and software so the ECM controls the T42 just like they had in the Gvans (with 4L80's in them.._).... just getting there is a pain.... my car has been ready since August except for this damn controls software issue messing me up... the TCI way I would have ran it this last fall..... but oh well... trying something a bit different... I am jealous you got yours done already... but I am lazy when it comes to shifting.... thats why I didnt go the 400 route....

ps.... what is this about boost in you signature.... you got something going also on that?..... :wall:
Gotcha. Yeah after I got the NA record, I decided to change it up a bit. Ripped out my cam, heads, etc and put it back together with some different things and a blower. Pretty mild 10PSI setup right now while I test things out. After I get the trans and fuel sorted out, I plan to run 15PSI or so. Not sure if I'll get the power I want without more cubes... we'll see. But at least the rest of the car will be ready, getting stronger from the rear back.
 

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Discussion Starter · #17 ·
Should be plenty of room, certainly more then with the 6L80. Probably just remove the heat shielding from the tunnel and you have the room.

You doing an Ultra bell and all that fanciness?
 

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Discussion Starter · #20 ·
WHERE are the pictures?!
lol I know I know, finally here we go!

Comparison pics... 6L80 and TH400


TH400 in the car:


Stock cross member works!


Shifter removed:


Removed TCM:


All the crap that comes out of the 6L80 that needs to be plugged in:


Fitting B&M Shifter:


Then a little test:

I still have a few tweaks to make in HPtuners that I found. We are going to pull the trans back out to build it for some power, this was just a test to see that it would work and wouldnt have any gremlins holding us back.
 
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