5.3 lm7 to a 4l80e whats needed?

Edmduncan

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Dropping a 5.3l lm7 into my 1991 c2500 that has a 4l80e factory.
I've read I may need a adapter coupling for the shaft on yhw flex plate but do I need a dished flex plate as well?
I've been reading conflicting information and some say it will bolt right up with just the adapter and others say you need a adapter , dished flex plate, longer bolts etc..
Can someone set me straight and fill me in to exactly what's needed to drop the lm7 in and bolt it to the existing 4l80e. Just looking for the info on the trans.
 

stutaeng

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Just get a replacement GMT800 2500HD/2500/6.0 flywheel from the local parts store. It has that adapter spacer already included. That's what I used on my L59/4L80e, from Advanced Auto Parts. A few years ago it was only like $65 though: https://shop.advanceautoparts.com/p/atp-automatic-transmission-flex-plate-z-270/10087518-P

...or junkyard flywheel from the same combo.

You can get it cheaper thru Amazon it looks like. I had bought the GM Performance equivalent at Summit, but then discovered that ATP was an OEM replacement that would work, and much cheaper. I returned the Summit one.

Also get the matching bolts. They are longer.

How are you controlling the transmission?
 
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0xDEADBEEF

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I think you need the 6.0 starter too. I think it has a longer snout to reach the flexplate. Check the partnos on rock auto to be sure.
 

stutaeng

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I think you need the 6.0 starter too. I think it has a longer snout to reach the flexplate. Check the partnos on rock auto to be sure.
Could that be on that rare 1999-2000 LQ4 that had the longer crank and iron heads? That's the only exception that mates directly to the 4L80e...no adapter required on that one.

I used the starter on my 5.3 that originally had the 4L60e from the donor vehicle.
 

0xDEADBEEF

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I thought the longer crank just eliminates the spacer. The end result is that either way the flexplate is back .500" or whatever it is.

It's possible the 5.3 starter is longer than it needs to be and works in both cases. Worth a check.
 

Dropped88

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The 5.3 starter will work with the 80

You need the mentioned above 6.0 flywheel and spacer.

Unless it was the 99-00 6.0L that had the longer crank and those didn't need the spacer
 

Edmduncan

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The 5.3l lm7 is out of a 2001 gmc sierra.
Yhe 4l80e is what came in my truck k bolted to the factory 5.7 that I'm swapping the lm7 into so am I wrong in saying the 4l80e is already controlled by my chevy? Or do I have to flash the new ecm to accept the 4l80e?
Oh I have the full harness and everything inc starter even. the flex plate is still on the 5.3l but it was mated to a 4l60.
 

stutaeng

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There's a difference between the 91-93 4L80e units and '94+ and has to do with the pressure control solenoid and something about cleaning cycle. I don't know the specifics. The ATSG rebuild manual talks about it also. You can look at the ASTG manuals on-line. I don't know if you can swap things to make it work with the newer ECU controlling.

There's a bit of information related to this here:

Page 5.

The 91-93 also had a "bolt-on" main electrical connector that got a service bulletin to upgrade to the current connector. I've never seen what that connector looks like.

If you use the LS park neutral switch, you will need to change the shift shaft on your 4L80e. (The older shift shaft is short like the TH400). I did this to a 1994 unit, but my unit had the threaded holes already there on the bosses, not sure on the 1991 if that will be there. Look here: https://www.gmt400.com/threads/4l80e-early-design-comparability.49999/page-3

I hope this helps.
 
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Dropped88

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You need to upgrade trans harness if it's not done. And that's a direct swap

The 5.3/60e harness needs trans connector repin for the 80e. They also make a patch harness you can use also that'll apapt the 80 trans to the 60 harness.

And last the tune needs trans part of tune segment swapped to an 80e segment.

I have a already segmented tune if you or someone you is gonna use hptuners
 
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