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TH400 Swap!

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Old 01-24-2012, 01:55 PM   #1
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Default TH400 Swap!

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.

Comparison pics... 6L80 and TH400
Click the image to open in full size.

TH400 in the car:
Click the image to open in full size.

Stock cross member works!
Click the image to open in full size.

Shifter removed:
Click the image to open in full size.

Removed TCM:
Click the image to open in full size.

All the crap that comes out of the 6L80 that needs to be plugged in:
Click the image to open in full size.

Fitting B&M Shifter:
Click the image to open in full size.

Shifter removed:
Click the image to open in full size.

Driveshaft Shop 9"
Click the image to open in full size.

Roll bar designed to allow rear seat use:

Click the image to open in full size.
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Drivers Seat:

Click the image to open in full size.
And the engine bay!

Click the image to open in full size.

Then a little test:
http://www.youtube.com/watch?v=GoBiY...layer_embedded

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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Old 01-24-2012, 11:39 PM   #2
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Props on making this work.
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Old 01-24-2012, 11:49 PM   #3
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Very nice! Hope better upgrades come for the a6. Seems like a step backwards
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Old 01-25-2012, 01:51 AM   #4
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Props on making this work.
Thanks!

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Very nice! Hope better upgrades come for the a6. Seems like a step backwards
Every other car I own is manual... I've hated the 6L80 since day one. Step forward for me! Next step would be a manual swap.
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Old 01-25-2012, 06:26 AM   #5
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Have you ever broke the 6l80?
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Old 01-25-2012, 09:24 AM   #6
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Have you ever broke the 6l80?
Thats the reason for the swap... my 6L80 was toast after two track days with the blower. It wouldnt hold any power on a sticky tire, just slipped. I looked at rebuilding the 6L80 but its fairly pricey with no guarantee that it will hold the power so I decided to go with a proven option. Plus the slow 3-4 shift of the 6L80 was really slowing me down at the track and I was sick of the electronic delays.
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Old 01-25-2012, 10:33 AM   #7
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sounds like you needed more tuning work done to the trannys computer
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Old 01-25-2012, 11:43 AM   #8
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sounds like you needed more tuning work done to the trannys computer
lol You cant tune out burnt clutches. My 6L80 lasted 62k miles and hundreds of quarter mile passes which is longer then some have lasted. My tuner did the best he could and I made improvements after logging many passes at the track. The trans held up ok for NA use and went 11.3 on motor, and 10's on spray so it was shifting fine and our tune was spot on. However with the added power/torque from the blower the trans just couldnt hold it. A 4k lb car with sticky tires and decent power is asking a lot from a stock trans.

Every single person I've seen with 550+whp, sticky tires, and repeated track use has had issues with the 6L80 holding, being consistent, etc.. Some decide to get Century to rebuild it, others do 4L80 swaps, etc.. but they have to do something.
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Old 01-25-2012, 11:58 AM   #9
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Ahh ok. 550whp still aint to shabby for a factory unit though an upgrade over the 4l60e anyways
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Old 01-25-2012, 02:24 PM   #10
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Nice work Sky. When did you get the blower?
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Old 01-25-2012, 02:30 PM   #11
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Nice work Sky. When did you get the blower?
Thanks, decided to change things up end of last year.
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Old 02-09-2012, 06:52 PM   #12
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Changed to a Holden sedan manual file and it works great without the TCM plugged in!
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Old 02-09-2012, 08:32 PM   #13
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very interesting thread
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Old 02-09-2012, 08:32 PM   #14
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I think this makes like 3 G8s running this trans now bring on 2012 lol
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Old 02-12-2012, 08:53 AM   #15
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I think this makes like 3 G8s running this trans now bring on 2012 lol
Who are the three running it? I know gr8lover did a 4L80 swap to back up his big cube F1 setup and was working on getting the electronics working. One guy did a manual TR-6060 swap on his blower car. Another G8 owner purchased a TH400 but I dont think it ever made it in the car and is now for sale. Wreckwriter is planning to do the swap soon and currently acquiring parts. Other then that I dont know of anyone thats completed a trans swap on a G8.

I'm impressed that times got knocked down so much in 2011! I agree 2012 is gonna bring some fast times for sure, I know I'm not gonna stop making mine faster anytime soon.
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Old 02-12-2012, 10:27 AM   #16
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Its just you and me Sky, unless there's someone out in the wild doing it. Yours is the only one running, for another month or so....
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Old 02-12-2012, 03:12 PM   #17
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Who are the three running it? I know gr8lover did a 4L80 swap to back up his big cube F1 setup and was working on getting the electronics working. One guy did a manual TR-6060 swap on his blower car. Another G8 owner purchased a TH400 but I dont think it ever made it in the car and is now for sale. Wreckwriter is planning to do the swap soon and currently acquiring parts. Other then that I dont know of anyone thats completed a trans swap on a G8.

I'm impressed that times got knocked down so much in 2011! I agree 2012 is gonna bring some fast times for sure, I know I'm not gonna stop making mine faster anytime soon.
You and wreck and i thought someone else but i may have been mistakin i didn't mean as in they have had it just that they are commited and 2012 will be with this set up. This is gonna be a nice year for the G8s i wish someone would to a 1000+ rwhp blown set up and i really wish it was me lmao

I'm ready to see all these new set ups go down the 1320 including mine
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Old 02-12-2012, 07:11 PM   #18
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Its just you and me Sky, unless there's someone out in the wild doing it. Yours is the only one running, for another month or so....
Yours should be fairly straight forward since most if not all of the details are figured out. The only gotcha I have left is getting the key to come out with the stock shifter unplugged. I know its only two wires I've just been focusing on other things, should be easy once I set aim on it. I took mine out for a maiden highway voyage this weekend to get the first 100 miles on her, so far so good.

Actually theres another gotcha now that I think about it... I havent wired up reverse lights yet. Not that you really need them.


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You and wreck and i thought someone else but i may have been mistakin i didn't mean as in they have had it just that they are commited and 2012 will be with this set up. This is gonna be a nice year for the G8s i wish someone would to a 1000+ rwhp blown set up and i really wish it was me lmao

I'm ready to see all these new set ups go down the 1320 including mine
Yeah most people are still pushing the limits of the stock block, really only Dan has gone to a different block and pushed it. Some others have bigger cubes but arent pushing the limit, just street cars. I'm waiting it out until my block calls it quits... then it can get crazy, haha.
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Old 02-12-2012, 07:21 PM   #19
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Hmmmm... Didn't know there was an issue getting the key out. As long as it turns off I guess I don't really care. I won't use or need reverse lights as my transbrake requires neutral and button push for reverse.

Same here on the block, run it til it ***** the bed.
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Old 02-12-2012, 07:29 PM   #20
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The key comes out if you leave the stock shifter assembly plugged in, unplug it and the key wont come out. Shouldnt be too hard once I look at the wiring, jump two wires and should be good.
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