62c10

So there's a lot here on 4l60e to 4l80e and T56 to either auto but not a lot for the truck guys. So what I have is a 99 silverado all stock with a 4.8 and a nv3500. I also have a 2003 chevy express with a 5.3 and it used to have a 4l60e (parts rig). And I also have a 2001 4l80e. I want to put the 4l80e in my Silverado. Can I use my 03 harness and pull the trans wiring from it and add it to my 99 harness and do a reflash for 4l80e? Or do I need to find a 4l80e harness? Or is reflashing my 99 pcm to run a 4l80e even possible? Thanks for any help. Mike.

Paul Bell

iTrader: (9)

Good call moving this to the transmission section.

My response still stands:

The wiring in the harness for the auto transmission starts at the PCM so in all likelihood, a harness for a stick vehicle needs to be swapped out to use an auto.

If you have an adapter that'll go from the 4L60E plug to a 4L80E plug, great BUT you'll still need a tune to use the 4L60E.

62c10

Well I actually just found the Speartech 4l80e harness add on. It goes all the way from the pcm to the trans. Should be all I need as far as wiring, plus a reflash. Any thoughts on this?
http://www.speartech.com/product_p/4l80eaddon.htm

Paul Bell

iTrader: (9)

Yes, that's a very nice harness. After it's installation, you should only need the tune for the 4L80E.

Let us know how this works out!

62c10

Will do. I guess I just needed to look a little harder for the part I was needing. Now I just need to figure out what flex plate I need for my long crank 4.8. I think just a flat flex plate with the spacer on the end (further from the engine) is all I need.

Paul Bell

iTrader: (9)

Well you'll certainly never break a 4L80E behind a 4.8L engine.

Choosing a flex plate: They're listed as different numbers at Rock Auto. They have a 4.8L engine with the 4L80E transmission listed in a 2008 3500 Express van. I'd say that's the one but there may or may not be a needed spacer.

62c10

Well my 4.8 is a long crank version. Doing some reading on it now. Looks like dished flex plate with spacer on the end. Dished flex plate to have clearance for converter bolts. And the spacer to hold the converter snout.

62c10

Lucked out today, found a 4wd 4l80e wiring harness at the local pick-n-pull for 14 bucks. Just need to grab some pcm pins and I should have my harness ready.

Jake's Performance

iTrader: (2)

If it's a long crank you need a flat flexplate and no spacer.

62c10

Ah thank you. Odd as it seems it's hard to find good info on a stock setup (early 6.0/4l80e)

Circle-D_Brian

Interesting about the 4.8 long crank.

-Brian

62c10

The 99-00 4.8 were long crank if the truck was originally a manual trans. I also already have a dished flex plate if for some reason I'm wrong so I may just buy a spacer and bolts so I have everything if I end up needing it.

62c10

So I'm trying to get my trans plug all labeled so I found this link.
http://lt1swap.com/99-02_vortec_pcm.htm
and this transmission plug pin out. (Post #2 4l80e connector key)
http://www.performancetrucks.net/for...g-swap-413157/
But the only ones that match are shift solenoid a and shift solenoid b? Which go to the red pcm connector pins 47 and 48. Any suggestions or help here? Thanks.

62c10

No body?

62c10

Is my question in post #13 too vague or something? Or does no one know?

Paul Bell

iTrader: (9)

I can't help, I've never done this swap.

You may need to consult somebody like Speartech-but they may only support something they've sold.