GM Tech Question

[SuperCab]

I know some of you don't like to see anything non-Ford related on here, and I apologize to those of you who feel that way. That being said, I've asked this on a few Chevy/GMC forums and nobody seems to know. Big surprise...


My 1987 GMC Suburban. It has a THM 400 transmission, which is basically chevy's C6.

I'm putting TBI (throttle body fuel injection) back on my Subby now that I have the time and money to put into it.

I wanna know if I could put a 4L80E transmission in where the THM400 is.

4L80E as some of you will know, is basically GM's E4OD.

If I take the trans, wiring harness, and ECM from a donor with TBI, and plug it all into mine, I don't see how I could go wrong.

If you had a Gen 8 or 9 Ford with a 351 and C6, and wanted to put an E4OD in it, could you take the E4OD, wiring harness, and ECM out of a donor with a EFI 351 and plug it all into your rig? I think it's the same thing.


Thanks for any input you guys can give. I think I know where I can get a 4L80E for cheap and if I can't come up with any major problems in this plan, I think I'm gonna go for it. I got 3.73s to replace the 4.10s, and with the lock up TC and .75 OD in the 4L80E, i should be able to get 14-15 mpg out of this old beast. as it is, i can usually get 10-11...


Also, advice on putting a 460/E4OD in will also be considered

Thanks!!!

 

[DNFXDLI]

I wish I could help..I haven't farted around with Chev's in 25+ years..I do know that a TH350 can replace a Powerglide behind a 327 though

 

[SuperCab]

I really didn't get much of a response from the GM forums... It's too outside the box for them. I kinda like putting fuel injection and electronics where they don't belong. After learning about the stuff when I got that '87, I realized it's all pretty simple. And TH350 > Powerglide

 

[smokey]

Don't see why you couldn't.
That should work you may have to upgrade the fuel pump to get the added pressure the TBI would need.
Not sure if they changed much block wise over the years in the trucks. You may run into a problem with the dash connections. I have helped guys swap newer parts in to their old Chevy's gotta get wrench time in since the fords seldom break down.

 

[O'Rattlecan]

Moved the thread to general automotive

Ryan

 

[aussie_f350]

I'm not sure but wasn't tbi only on roller cammed engines? Also you can get a non electric 4 speed auto we call it a t700 over here? Easy replacement for t400

 

[SuperCab]

Yeah, t700 I assume is what we call 700R4... it's a th350 based, while the 4L80E is th400 based, and comprable to a c6 in strength. It's a 3/4 ton suburban and I tow with it regularly, so the added strength of the 4l80E is needed. Unfortunately 4l80e only cane as an electronically controlled unit.

It came with tbi from the factory (GM started TBI-ing everything in '87) so it has the in tank pump still hanging out and the appropriate dash connections.

I think it will be 100% plug and play as far as electronics go, the only thing I'm worried about is where the ECM harness plugs into the firewall on the driver side... there is a big plug here just like a ford, and it is in 3 pieces. wires to the nose lighting (headlights, markers, turn signals), underhood (main keyed hot comes and goes through here, as well as power for everything else inside), and the ecm power, and signal for the check engine light goes here too. I'm afraid the donor is not going to plug in here with all the right pins. hopefully the only thing left out might be gear shift indicator, which I'm gonna have to rig up anyway since the 400 is rod shifted and the 4l80e is cable shifted...

I guess I am looking for a go ahead more than help, huh? Does anyone have thoughts on the shifter? I'd just go floor shift but the 4x4 shifter is right in the way on these...

 

[kiwi f150]

Cant see why it wouldn't work - maybe you could buy a complete running damaged truck with all the gear in it and just swap it over which would make it easierfor you as you would then know where every thing went and how it was routed.

 

[SuperCab]

that's more or less what I have in mind... I'm kinda excited, I think it's gonna turn out pretty well. With the trans and axle swap, it should drop my RPMs at 75 from almost 3600 to 2300... should be pretty nice.

 

[73F100Shortbed]

I don't see why it wouldn't work. I also like how you turned your post to relate to Ford.

 

[Fellro]

If you get a complete harness from one with a similar body, should be able to do it. The Suburbans kept the same body and dash until 91 if I recall. Took the harness out of the BIL's rusted out hulk of a Suburban, they actually have a harness that runs into the passenger side of the firewall, just behind the motor. The ECM is up behind the glove box, and the harness is nearly stand alone. The trick is that the 4L80's didn't show up until 91.

 

[polarbear]

I really didn't get much of a response from the GM forums... It's too outside the box for them. I kinda like putting fuel injection and electronics where they don't belong. After learning about the stuff when I got that '87, I realized it's all pretty simple. And TH350 > Powerglide

You may be the first person in history that wants to swap a THM400 for a 4L80E, that's why. Usually, the question is the other way around.

Other than that, I don't see why not. Do you have a shop that does resto-rods in your area? They'd be the peeps to ask- lots of experience adapting modern electronics to older vehicles.

 

[SuperCab]

If you get a complete harness from one with a similar body, should be able to do it. The Suburbans kept the same body and dash until 91 if I recall. Took the harness out of the BIL's rusted out hulk of a Suburban, they actually have a harness that runs into the passenger side of the firewall, just behind the motor. The ECM is up behind the glove box, and the harness is nearly stand alone. The trick is that the 4L80's didn't show up until 91.

Yeah, but anything 91-96 that has a TBI 350 and a 4L80E should make a suitable donor I think...

I think the 4L80E is the heat, man... There's one in my '98 Suburban and it's great... Lock up TC and overdrive... TH400 can't compare.

 

[Fellro]

Won't be plug and play, they changed it all with the new body. You could adapt it, but it won't be as simple as switching the harness.

 

[SuperCab]

Do you know if there were old body style '91s with 4L80E trans?

 

[dragogt]

This may hep you out some..

http://www.pirate4x4.com/forum/showthread.php?t=975381

 

[Fellro]

91 would be the only year you could have both the harness from the old body style and a 4L80. The 3500 and Suburban was the only body to get it from for that year.