4L80E leak

[Wozny]

I have an all stock 92 3/4 ton and the 4L80E tranny is leaking 2 quarts of fluid n the first 35 miles, then just completely stops leaking at two quarts down. I haven’t driven it much since I got it but I think it does drive OK at two quarts down, not sure. It does shift fine when it’s low ir full, but when it’s real cold, and low, it won’t. Does this kind of leak indicate where the leak might be? It leaks onto the exhaust pipe mostly, on driver’s side of the part of the pipe that goes left to right, parallel to the bumpers. But it drips in other places too. I’m thinking it’s coming from above the bell maybe, but I’ll take another look. It’s definitely not from the rear of the tranny. I’m hoping it’s from a cooling line so I don’t have to pull it. Thanks

 

[stutaeng]

Yeah, figure out where it's coming from before you burn up the transmission...or the truck catches fire!

 

[Wozny]

Thanks, didn’t think about a fire, I’ll carry an extinguisher if I drive it to the transmission shop for sure

 

[stutaeng]

If it is not leaking from the rear tailhousing and from the oil pan, only logical place is the cooler lines on the passenger side or the front (torque converter, front seal or pump).

The vehicle speed sensors are on the driver's side, look at those also, but not likely to leak that much from there.

Also look for the vent hose. The early transmission units had a short hose directed on the passenger side near the exhaust. They changed to a much longer hose directed on the driver's side on the early 2000s, supposedly because if the vent line expelled hot fluid on the exhaust, the vehicle could catch on fire.

You can easily upgrade to that late vent hose style if you want, just pull one from the junkyard.

 

[Wozny]

Thanks, it sure seems like the drivers side but it’s all over. Can the vent leak that bad? Maybe when not tight fitting? Wouldn’t the front seal and TC leak from bottom of Bell? This is from higher than bell bottom. Where is the pump?

 

[tpass]

the fact that it leaks 2 quarts, then stops leaking rules out any of the lines or coolers, they would leak until there is no fluid left to pump.

When I pulled my 4l80e the dipstick tube was rotted, would leak when i put fluid in. It could be the tube o-ring as well?

 

[JOHNGAAA1]

These 4l80 transmissions are notorious for leaking out of the electronic plug on the left side. The o ring dries out.

 

[stutaeng]

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.

 

[Supercharged111]

A leaky trans is a death sentence.

 

[Wozny]

Thanks, I’ll check and see if I can find that O ring, I can afford that!