4L80E leak

Disclaimer: Links on this page pointing to Amazon, eBay and other sites may include affiliate code. If you click them and make a purchase, we may earn a small commission.

Wozny

I'm Awesome
Joined
Aug 4, 2019
Messages
109
Reaction score
39
Location
Bozeman
T
What is the history with truck? It's always been okay until recently? Or you just bought it?

The passenger side has the cooler lines,the dipstick seal (no oring) and maybe the vent tube (it can be either side. ) The vent tube should not be releasing fluid unless there's something else going on. Is your dipstick level correct? The level fill level should be even with top of the pan. Only way to check is to remove the pan and check.

On the driver side there's the electrical connector, speed sensor and the shift shaft seal. I would not think any one of those would leak that much fluid...oh on that side there's also the pressure test plug.

Then there's the front that has torque converter and front seal. Pump-to-case gasket and bolt heads can leak.

Hook up a longer hose on the vent tube and stick an oil jug or something. Go for a short drive and see if there's anything inside the jug.
hanks very much for the pictures, where is the pump? It seems to be coming from high up and in front.
I bought it two years ago and have only driven it twice since then, just to go on 60 mile trips. I drove it 130 miles to get it home when I bought it, the guy I bought it from didn’t tell me about the tranny leak, but I bought it for 1200. Now I know that it went at least 100 miles while 2 quarts low. Who knows if it was full when I left Billings. Or if he ever drove it full. The truck has a straight and rust free body so I don’t think I got ripped off. Will take a closer look at it now. Thanks again
 

stutaeng

I'm Awesome
Joined
Aug 7, 2019
Messages
3,410
Reaction score
4,348
Location
Dallas, TX
That's the pump on the second photo with the 7 bolts (unit is flipped upside down on this photo.) The torque converter slides over that shaft. You have to remove the transmission to access this. The red arrow shows the front pump seal. The bolts get sealed with these square cut ring washers on the bolt heads (blue arrow.)

The first photo is the pump removed. There's a pump-to-case thin gasket (where the green arrow is pointing). I think if that seal leaks the fluid will just fall inside into the case or go into another fluid passage. But there's another seal on the outside circumference of the pump (yellow arrow.) I can see fluid leaking externally if this seal fails.

I hope this helps.
 

Attachments

  • IMG_20210904_000615167_LI.jpg
    IMG_20210904_000615167_LI.jpg
    288.1 KB · Views: 17
  • IMG_20211023_122803473_LI.jpg
    IMG_20211023_122803473_LI.jpg
    177 KB · Views: 16
Last edited:

Wozny

I'm Awesome
Joined
Aug 4, 2019
Messages
109
Reaction score
39
Location
Bozeman
These 4l80 transmissions are notorious for leaking out of the electronic plug on the left side. The o ring dries out.
Where is that electrical plug? Leak is definitely on the left side but I only see the two fuel lines and a big electrical harness there, which block my view of much of the transmission. The right side has no trans. fluid anywhere. Looking from the top, under hood, no oil visible. Thanks
 

Wozny

I'm Awesome
Joined
Aug 4, 2019
Messages
109
Reaction score
39
Location
Bozeman
That's the pump on the second photo with the 7 bolts (unit is flipped upside down on this photo.) The torque converter slides over that shaft. You have to remove the transmission to access this. The red arrow shows the front pump seal. The bolts get sealed with these square cut ring washers on the bolt heads (blue arrow.)

The first photo is the pump removed. There's a pump-to-case thin gasket (where the green arrow is pointing). I think if that seal leaks the fluid will just fall inside into the case or go into another fluid passage. But there's another seal on the outside circumference of the pump (yellow arrow.) I can see fluid leaking externally if this seal fails.

I hope this helps.
Helps a lot, thank you. Seems like since it does stop leaking it could be that front seal? Maybe the thin pump seal might leak all the fluid?
 

stutaeng

I'm Awesome
Joined
Aug 7, 2019
Messages
3,410
Reaction score
4,348
Location
Dallas, TX
Where is that electrical plug? Leak is definitely on the left side but I only see the two fuel lines and a big electrical harness there, which block my view of much of the transmission. The right side has no trans. fluid anywhere. Looking from the top, under hood, no oil visible. Thanks
On post #8, second photo. That's the green connector. Early 91-93 transmissions had a "bolt-on" connector that eventually was supposed to be upgraded to this type. If yours is original, you should probably upgrade it. I've never seen a bolt-on connector BTW.

They are common to leak fluid and cause strange things to to happen. Easy enough to remove the connector to see if there's any ATF inside. Remove the pan and un-hook up everything is easy. Costs about $60 for a new harness.

Helps a lot, thank you. Seems like since it does stop leaking it could be that front seal? Maybe the thin pump seal might leak all the fluid?
Yeah, the front seal would cause it to leak all the time. I'm not sure what could be the problem. Probably need to take it to a shop for diagnosing/fixing.
 

Wozny

I'm Awesome
Joined
Aug 4, 2019
Messages
109
Reaction score
39
Location
Bozeman
On post #8, second photo. That's the green connector. Early 91-93 transmissions had a "bolt-on" connector that eventually was supposed to be upgraded to this type. If yours is original, you should probably upgrade it. I've never seen a bolt-on connector BTW.

They are common to leak fluid and cause strange things to to happen. Easy enough to remove the connector to see if there's any ATF inside. Remove the pan and un-hook up everything is easy. Costs about $60 for a new harness.


Yeah, the front seal would cause it to leak all the time. I'm not sure what could be the problem. Probably need to take it to a shop for diagnosing/fixing.
In
 

Wozny

I'm Awesome
Joined
Aug 4, 2019
Messages
109
Reaction score
39
Location
Bozeman
Thanks, I think I see a terminal on picture 2314917, post 8, is that the picture 2 you refer to?
 

stutaeng

I'm Awesome
Joined
Aug 7, 2019
Messages
3,410
Reaction score
4,348
Location
Dallas, TX
Thanks, I think I see a terminal on picture 2314917, post 8, is that the picture 2 you refer to?
Those are the speed sensors (circled in red)...This is the electrical connector.
You must be registered for see images attach
 

Attachments

  • 1649196948777.png
    1649196948777.png
    1.1 MB · Views: 9

udidwht

I'm Awesome
Joined
Jan 25, 2021
Messages
208
Reaction score
125
Location
Renton Highlands,HB Ca.,Fujieda-Japan
Where is that electrical plug? Leak is definitely on the left side but I only see the two fuel lines and a big electrical harness there, which block my view of much of the transmission. The right side has no trans. fluid anywhere. Looking from the top, under hood, no oil visible. Thanks
Gray connector sticking out is it. The o-ring is not generally what causes them to leak. They crack internally and leak into the connector causing shift/ing issues. If the crack is big enough it will leak out until fluid levels drops below the connector. Requires dropping the pan and replacing the connector (DIY job).
 

staples

Newbie
Joined
Feb 16, 2022
Messages
2
Reaction score
1
Location
Perth, Western Australia
On mine, the clips that hold the electrical connector in place were broken causing it to sit slightly off. The fix was a replacement harness/o ring connector (All one unit) and a new trans pan gasket.
 
Top