4L80e Swap Build Thread

Starting a build thread for my swap to a '97 4L80e from a 3/4 ton 4x4 burb in place of my original '91 4L80e.

Reason for a swap: later 4L80e had some mechanical and electrical upgrades, but the main reason is PCM. '91-'93 80e's used a very specific PCM that has virtually no support in the GM OBD I tuning world. And it's quite a bit more rudimentary than the next gen PCMs so it's difficult to get a good tune with a modified engine such as my vortec head 383. I have a '7427 PCM that was common to all 94 and 95, automatic full size pickups, burbs, Tahoes, etc. - regardless if 4L60e or 80e. Way more support for it on sites like Gearhead EFI and thirdgen.org.

Tonight I finally took the pan off the '97 tranny to take a look inside. Mostly just to see if there was something obviously wrong (i.e. chunk of something in the pan) before I take it to the tranny shop for them to go through it. Looked pretty clean to me. Almost nothing on the magnet and the remaining fluid looked and smelled OK. Tranny came from a parts rig that I bought sight unseen from an auction outfit. Engine barely ran - it was all I could do to get it up my steep driveway and into my shop. So no real test drive, but it did go forward and backward. (A lifter had grenaded and did a ****-ton of damage, incredibly loud clanking when I finally got it running)

Well...might have to rethink plans here a bit. Multiple people have recommended the shop I took it to, and they're obviously knowledgeable about GM truck transmissions, but they're quoting me $3K to go through it. Pretty rich for my blood, especially when I already have a working 4L80e in the truck, without any apparent issues. But I still want to be able to safely upgrade my PCM so I need to do something. The two primary options I see:

1. Same shop has quoted me about $700 to modify the '91 trans to be compatible with the later PCM. You have to use the force motor from a later trans and possibly modify the valve body or also use one from a later trans. The quote was before I had the '97 trans so I don't know if they could use parts from the newer one in this option. Might be better to just keep the '97 intact so I can sell it as a complete core.

2. Use the '97 as a core and go with a decent reman for about $2k. Problem is what's a decent reman? Pretty much whatever you read online points to the fact that all the reman outfits suck! I am willing to entertain other points of view here - if anyone has other input on remans let me know.

A distant third option would be to install the '97 as is and take my chances. I think the rig had 200k on it and the torque converter wasn't painted so it sounds like the tranny was original - probably a poor option.

Tranny is at the shop now but they probably won't get to it till later this week. I need to figure out if I want them to go ahead and tear it down and check condition of everything or give up on using it.

From what I was researching a complete upgraded 4l80e is almost $2k in parts(including torque converter, billet parts etc...). For stock 4l80e should be much cheaper. Jake's been referenced a lot for 4l80e builds with some bad reviews sprinkled around. But their build is also around $3k. From what I have seen, they seem to charge almost $1500-$2000 for actual labor and use of tools. Finding someone to just refresh it might be cheaper.

Best option is to leave the thing alone with existing ecm.


I would not put any unknown transmission without a rebuild ever again. Had a 50/50 success rate and don't want to mess with that chance again unless it is truly a beater I don't have a care for

Side note: 4l80e can last 300k+ miles. 230k miles on my 97, and was 250k miles on my old 94. But for a new install, at least refresh. I started doing transmissions my self as I lack the funds to pay someone else to do it.

Another side note, just sell me the burb

Jakes Performance is a well known 4L80 guru. I have used lots of his parts, and talked with him many times. He is a good guy, but he is also a no nonsense type of gut that rubs some the wrong way. He gets a bad reputation from people who either want to cut corners, or refuse to buy what they really need. He use to sell lots of parts, but he said he got tired of dealing with people who blame him for builds intended for 1000hp, but end up behind 1500hp engines. Of course, when something breaks, it’s his fault.

If the fluid and pan is clean, that would be a good sign. If the outside of the pan is just as greasy as the rest of the trans, that’s another good clue. If the transmission is caked with dirt and crud, but the outside of the pan is clean, chances are the filter/fluid has been serviced. Who knows what the actual condition is?

yevgenievich said:

From what I was researching a complete upgraded 4l80e is almost $2k in parts(including torque converter, billet parts etc...). For stock 4l80e should be much cheaper. Jake's been referenced a lot for 4l80e builds with some bad reviews sprinkled around. But their build is also around $3k. From what I have seen, they seem to charge almost $1500-$2000 for actual labor and use of tools. Finding someone to just refresh it might be cheaper.

Best option is to leave the thing alone with existing ecm.


I would not put any unknown transmission without a rebuild ever again. Had a 50/50 success rate and don't want to mess with that chance again unless it is truly a beater I don't have a care for

Side note: 4l80e can last 300k+ miles. 230k miles on my 97, and was 250k miles on my old 94. But for a new install, at least refresh. I started doing transmissions my self as I lack the funds to pay someone else to do it.

Another side note, just sell me the burb

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LOL! I've spent too much on this thing now - I don't know if I'll ever be able to sell it!

You're right about all, including I should just keep current trans and PCM. But that original PCM is just so finicky with the different cam, increased displacement and compression, etc. I'm going to talk to the shop and see what they say. I may just pay them to take it apart and get a condition assessment on the '97 trans. I've been wondering if the '97 valvebody and force motor can go in the '91 which would then allow me to run the newer PCM.

I've been intrigued with the idea of doing the work myself, but I'm not sure 4L80e is a good place to start with auto transmissions? I do have the ATSG manual for it, but don't you need several expensive tools just to get them apart?

The 4L80 is basically a 400 trans with a overdrive clutch in front of the forward clutch housing. If your comfortable with a 400 trans, the 4L80 isn’t much different. A lot of the parts interchange between a 4L80 and 400. Hydromatic replaced a lot of thrust washers with bearings, which brings up another potential problem. The early 4l80 and 400 use the same bearings, they interchange. The later “center lube” bearings are unique. Use old style bearing in a late model, the planetary gearsets will burn up from lack of oil. You also have to use the correct style fitting for the cooler lines, or the transmission will burn up.

The biggest pain in the ass with a 4L80 is the overdrive piston assembly. GM does “require” a special tool that includes seal protectors and fixtures to hold things in place. I have the tool, it’s not worth the expense. It can be done without the tools, it requires ALOT of patience. If you decide to tackle it, pay close attention to the orientation of the lip seals. I’d suggest putting it together with the old seals first just to get a feel for how it’s suppose to go together. That way if you cut a seal, it’s no big deal, you practiced with the stuff you would normally throw away. Once your comfortable with putting it together, put the new seals on.

If you have the transmission out and apart then I’d suggest the Jakes Performance or CK performance shift kit. It’s a much better design, but it can’t be installed with the trans in the truck. The TransGo kit is limited by its design, but can be installed with the trans still in the truck, it just doesn’t work as well.

I think the pressure control solenoid will interchange between early and late models, but the internal wiring harness also needs to be changed to match. I know that information is covered in the ATSG book.

Trans Shops are Big time rip offs. A rebuild kit good for 800Hp all day everyday is about $500/$700 (4L80e) Clutches/bushings/solenoids/bands ECT! more parts thans a trans shop puts in. After getting ripped off from trans shops I build my own. You would not BELIEVE how cheap performance parts cost. You pay BIG TIME for labor $$$$$$$ and your not even getting a FULL rebuild from 90% of the shops.

Nasty-LSX said:

Trans Shops are Big time rip offs. A rebuild kit good for 800Hp all day everyday is about $500/$700 (4L80e) Clutches/bushings/solenoids/bands ECT! more parts thans a trans shop puts in. After getting ripped off from trans shops I build my own. You would not BELIEVE how cheap performance parts cost. You pay BIG TIME for labor $$$$$$$ and your not even getting a FULL rebuild from 90% of the shops.

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^ Agreed ^
The go fast parts and diy is much much cheaper than the alternative, with some dim wit who doesnt do it right completely, or cuts corners on a build.

Already seen now several "builds" that werent complete thru and thru.
Doing it yourself takes alot of time, and patience, but to clarify alot of the redneck lore and mysticism that surrounds automatic transmissions : its not that ******* bad to do, its like how the HVAC people ive learned keep their trade a big secret or hell, how tool and die makers like myself keep the trade a big secret... job security.

Obv OP, do whatever you are comfortable with. Doesnt have be diy, time is money. No if ands or buts. If its morr profitable to let someone else do it, by all means have them do it.

Most of the tools can be either recreated or gone around a different way of installing. But decent assortment of tools is needed. With absolutely no experience, i would likely recommend someone else do the refresh. I am slowly getting ready to tear in to the 4l80e. Been through 700r4, 4l60e and th400 before. Each one takes a lot of time without experience.

For anyone willing to learn transmissions. I mean STEP by STEP on video and so easy your
step children can do it. I learned from this guy years ago. THE BEST VIDEO MADE you will
ever find ANYWHERE. And he shows what to look for good and bad. Tips n tricks to.
If you buy his rebuild kit you get the video. Or just pay out right for the USB.

Transmissionbench.com Really great guy to talk to and wont rip you off. Here is one
of his videos. They are Incomplete on youtube. The videos are just to show HOW DETAILED
they are. I learned how to do complete stock rebuilds from him/videos. You learn to do mods as you go and buy performance parts.

Lets not forget the 4L80e

with all his video's you cannot put it back together wrong PERIOD!!

Nasty-LSX said:

Lets not forget the 4L80e

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This is great, I’m in! Seems to be well worth $60. I started watching the free introductory video and I’m digging his homemade jigs and tools - that’s totally me.

Thanks for sharing.

Thanks to all for the input on rebuilding. All good advice. I talked to the shop today and I think here’s the road I’m heading down.

I told him not to proceed with the $3k build. We started talking about mods to my existing ‘91 trans to make it fit for the later PCM. There’s lots of chatter on various boards about why this is bad, but he’s done it before, has had good results and will stand behind the function of the mods, although not the trans itself, which makes sense because he’s not rebuilding. Mods mainly consist of a Trans. Go kit and the best part is trans does not need to be removed. Also, My trans is actually a ‘93 Goodwrench replacement - it has the updated external wiring connector which he says is a good sign it has the updated force motor anyway. I’m not so sure about that after my internet research, but we’ll see. He said if he can keep the ‘97 trans, he’ll charge me about $300, but I’m going to see what he’ll do it for if I keep that trans because.....

Part B would be me eventually rebuilding the ‘97 trans. Probably based on the videos that @Nasty-LSX posted. My current trans shifts great with no apparent problems at all, but it won’t last forever and the later L80e had much improved cooling over the early. Besides I think I just want to try and rebuild a trans. One of the few things I haven’t done yet.