Tell me about the 4L80E tranny

[david85]

Hi guys,

My dad's truck is a 1993 GMC 3500 non dually 4wd and is powered by a none ECU 6.5 turbo with the 4L80E transmission.

The tranny developed a leak in the last few days that seems to be oozing from the bellhousing. My guess is the front seal.

There were some problems recently with hard shifting and overdrive not working (failsafe mode). Replacing the TPS cured that, but now this happened about a month later.

I'm not well versed with the GM trucks and if anyone can give me some ideas on what could be wrong with the transmission and if I have to rebuild the tranny what upgrades I should put in there.

I understand that this transmission can be prone to building too much line pressure and possibly causing a seal blowout.

Please share any experiences you have with this transmission because I will personally have to repair this truck and will need as much backround as I can get before I dive in.

Thanks

 

[lotzagoodstuff]

I've always heard good things about the 4L80E, that it's the no BS version of the Turbo 400 with overdrive, a super durable tranny that lots of racers who want to street drive their cars are utilizing. I don't have a lot of experience with them leaking, but I would guess that you just have a bad seal (you didn't say, but how many miles on this trans?). Given the hideous removal process, I would probably rebuild it while it's out as I don't think it's that difficult once it's out of the truck.

Good luck

 

[towcat]

find a trans shop with a Sonnax line flow tester. Pay for the diagnostic time. Depending on the miles on the trans, the trans oil cooler is restricted and the pressure is backing up to the pump seal.

 

[david85]

Thanks guys, it has 260 000 kilometers on it. Seems to be a nice transmission and shifts nice and firm with good engine breaking response time, but from what I've seen all the auto tranies of the early 90s had problems. Ford, dodge and GM. I have generally heard good things about the 4L80 though.

If it has to come out, I probably will be doing a complete overhaul on it. You never really know whats wrong with an auto tranny untill you tear it down.....

 

[david85]

Found the problem. One of the steel cooler lines has a rust pin hole. Other line is not much better in the same location. I'll replace them both.

 

[DIESELHERB]

Put 360,000 miles on my 4L80E brfore I replaced it(believe it was the TC not the trans) best trans. GM ever made! Odd for a manufactor these days.