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4L60E to TH400 question

4L60E to TH400 question

Postby LeadFootedRacer [OP] » Feb 17 2017, 2:04pm

I am swapping my 4wd 4L60E for a 2WD TH400 in my 2003 Yukon.

I will wire the neutral safety switch appropriately to the new hurst floor shifter and I will be getting the Dakota Digital VSS parts. I will also be getting the proper flywheel and spacer.

The fab work for the crossmember is a piece of cake, and I will purchase a yoke and have a new driveshaft made.

All that I have a question about is the tuning. I am building another motor for the truck, and stuffing it full of 80mm turbo goodness. But first, I'm ditching the 4wd components and swapping the trans. I daily the truck so my question is this;

How will the computer react to the missing transmission information? I will need to continue to drive the truck on a daily basis for 3-4 months while I finish up the turbo motor and swap it in. If at all possible, I would like to avoid paying a tuner to tune the truck twice.

An 80E is out of the question, so don't ask.
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Re: 4L60E to TH400 question

Postby bootstrap » Feb 17 2017, 2:43pm

Im gonna ask anyways, why is a 4L80E out of the question? Cost for cost, they can be built to the hilt like a TH400, should bolt up the same as a TH400, and are probably more common now than a TH400 is.
Obviously you've made the decision not to use a 4L80E, I'm simply curious why.

As far as driving it with a TH400 behind the stock motor with stock tuning? I wouldn't have any experience on that but I would think that at the least your going to be staring at a check engine light but I would think the engine will otherwise run normally. Maybe the computer will think its in park or neutral the whole time.
Since a TH400 swap into a newer truck like this is super rare(because theres no reason not to swap to a 4L80E instead), you probably will have to figure out the cross member mods and driveshaft length yourself.

Automatic transmissions don't have fly wheels. They have flex plates.
I would think this truck would have a hard time passing RI emission inspection. Something like this sounds like an off road/track only rig.
There is always enough time to do it over again, but never enough time to do it right the first time.
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Re: 4L60E to TH400 question

Postby LeadFootedRacer [OP] » Feb 17 2017, 2:59pm

Dollar for dollar, for Me, the swap is cheaper.

I have a race prepped 400 on hand, and just sent the converter out to be restalled for $100. Boom. Done. Needs nothing but a crossmember, yoke, and driveshaft. I have all the other parts. I'd be into the 80E swap for almost $2k between a core, refresh, and all that other crap.

I knew about the flywheel/flexplate terminology. I make the mistake ALL the time. LoL. It's terrible. It's like when people say "ORIENTATED". It's a word, but only to those that are not in the know.

A 2WD 4L60e and a th400 are very close in mount locations if I remember correctly. The 80e is a 3" cut and move on the crossmember, so I'm sure it's less than that.

I daily the truck, and have driven it in 3rd gear (same ratio as the th400 final) for a couple weeks and have zero complaints on how it's been on the highway. I actually like it better. Sure, gas mileage is about 3mpg less, but who cares about that crap, it's not a Prius.

Check engine light doesn't bother me. Been staring at an airbag light for a while now. I just want to get a few months out of it behind the stock motor while I wrap up the rest of swap.

I have till 11/18 on the inspection. Planning to move to mass soon (no emissions on 03 and older)
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Re: 4L60E to TH400 question

Postby LeadFootedRacer [OP] » Feb 17 2017, 4:32pm

I've been searching this a lot with no success, and the tuner I had planned to go to claims it will need to be tuned (after claiming it would run fine). I don't want to tune it twice and I think he's trying to soak me for the cost of a second tune.
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Re: 4L60E to TH400 question

Postby bootstrap » Feb 17 2017, 4:55pm

Well that answers that.
I look forward to info on how this turns out. I was once a pioneer in the automotive world. Not quite to this level but with other similar projects. Now I like to sit in the bleachers and watch, figuratively speaking of course. I get enough "wrench time" keeping these things running.
One thing you might consider would be to swap rear end ratios to 3.08 or such. You might actually improve your 0-60 times if you have enough power, and it sounds like you will.
There is always enough time to do it over again, but never enough time to do it right the first time.
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Re: 4L60E to TH400 question

Postby LeadFootedRacer [OP] » Feb 17 2017, 6:10pm

Hoping to be in the 6-700whp range and daily drive it. Going to keep the rear that's in it, in it till it blows. Got a lot going on with the project and that's last on the list. LoL.

I'm just afraid to do all this work for the trans and then find out it won't run. I can't imagine the PCM would shut down the motor or put it in such a limp mode that I couldn't drive it. Maybe lose ABS and other small time functions, but who knows.


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Re: 4L60E to TH400 question

Postby bootstrap » Feb 17 2017, 6:21pm

One way you can find out is get under there and unplug the trans wires and try to drive it. Trans will likely go straight to limp mode in 3rd gear but itll tell you if the truck will move and how well the engine will run.
There is always enough time to do it over again, but never enough time to do it right the first time.
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Re: 4L60E to TH400 question

Postby kingdouglas120875 » Feb 17 2017, 8:33pm

I have 2000 chevy Silverado it slips a little going from second into third should I be saving for a new transmission


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Re: 4L60E to TH400 question

Postby Onlyina_Chevy » Feb 17 2017, 10:27pm

Yeah, unless you're a great transmission mechanic.
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Re: 4L60E to TH400 question

Postby tzfbird » Feb 20 2017, 4:43am

If you put a 40 tooth reluctor on the output shaft and run the corresponding pickup from an 80s/90s TPI car or TBI truck it should send the correct VSS signal to the PCM. I have also done some research regarding converting from a TH400 to 700r4 in my truck and the torque converter lockup is used in the TH400 for the kickdown solenoid. I'm still working out how exactly but you can probably pick out the wires you need to run the kickdown since it will have the VSS signal for the speedo. I mention that just in case you don't want to mess with a micro switch mounted to the throttle or pedal.

If it were me I'd go with the 4l80e and just repin the connector but that's just me.
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