Hey guys,

Need some help.

4l80e in my truck is acting strange. If the gear selector is in the OD position, after a short time (1-2 miles or sometimes sooner) it'll lose all gears and just freewheel/clunk. But if the selector is in the D position all is fine.

Converter is fine, locks up great, doesn't slip. And 4th gear is fine too until it loses all forward momentum. Any ideas?

 

So in OD things go to hell?

If 3rd is selected, or any other manual selection of 1-3, all is OK?

If manual selection is made the overrun clutch in 1-3 is applied. OD does NOT apply this clutch in said gears. The forward clutch is applied in all forward gears in OD and manual.

Yer forward clutch sounds like its toast!!

 

That's exactly what it is doing. Thanks!

Glad to know, but it sucks since the trans only has ~10k on it

Couple follow up questions
1) Am I making matters worse by driving it it 3? Don't have the time to pull the trans at the moment
2) I'm assuming this means full rebuild?

 

I'm might be wrong about my analysis, but its based off what I'm seeing on the GM 4l80e guide. I'm not a pro.

If it is what I think it is.....

1) You're not doing it any favors. I'd sure as **** baby it if I had to drive it like it is now.

2) You're going to have to crack it open for sure. If the forwards are toast then you should figure out why they let go. If not old or behind a big engine then maybe you're not getting enough fluid pressure? That could be a pump, boost valve or other problem. I'd get a pressure gauge on it before its pulled to see whats going on.

 

Do you drag race in OD or 3rd? Much power?

 

The OD and forward clutches are first in the transmission stack, so they arent that bad to get to...

 

Sounds to me like it could be the roller clutch in the overdrive. The reason it holds in manual D-2-1 is because the 4th overrun clutch pack is engaged. That pack doesn't have much holding strength so you're probably having to stay out of the power or it starts chattering and slipping that too. If it is roller clutch failure you're unfortunately going to need to replace both parts of the assembly the roller clutch resides in - that includes the 4th carrier. When the rollers get a flat spot they chew up everything.

 

Nope. This is just a knock around truck with a stock 5.3 that occasionally pulls a lwn mower.
Hmm. Maybe it won't be a full rebuild then. But knowing my luck something else wilm break if I don't change it all.
Thanks. That's exactly what it sounds like. Crap

The whole point of the 80e swap was longevity...so much for that!