# 4l80e Question of the day



## mudduck72 (Apr 4, 2012)

I just bought a 96 suburban with the 6.5 and 4l80e. It is a 3/4 ton and 4x4. My question is..... The transmission shifts fine but when in overdrive at hwy speeds it drops out of overdrive so it feels like it is free wheeling. this only happens when going down a hill if its up hill or normal flat ground everything is fine.  When it happens if i give it more fuel she kicks right back into over drive. I do not feel like it needs a overhaul but really dont know. I checked it with the scanner and has no codes. I hope some one has had the same issues. I have searched a lot of forums and have not found my exact problem


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## jb1390 (Sep 23, 2008)

http://www.454ss.com/Articles_new/red/4L80E_Transmission_Problems.asp

Not sure if this helps, but there is good info here. Have you tried changing the fluid and filter? I would start there and see if it looks burned at all.

There is also something in the back of my mind that tells me excessive pressure on the cooler lines (from adding an aux cooler, etc) can cause something like this....but I don't remember exactly.


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## mudduck72 (Apr 4, 2012)

Yes it has had the fluid changed and filter also the servo valves The last owner did that. He thought it started acting up around the same time the day time running lights quit. I changed the brake switch last night on the regular pedal (non) emergency and it did not help. I still have yet to figure out why the lights quit but every thing on the dash tells me they are. I think that problem maybe the module behind the dash. I am not worried about that now one problem at a time i guess. I just want to make sure they would not be interlinked.


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## mudduck72 (Apr 4, 2012)

I will look at the cooler issue tonight. Thank you


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## mudduck72 (Apr 4, 2012)

I will look at the cooler issue tonight. Thank you


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## mudduck72 (Apr 4, 2012)

I pulled the pan last night and also took down the valve body. The fluid was discolored but did not smell. I am taking the valvebody down to tranny shop he is going to put a sleeve in it on one of the valves. I will report back on which one and if it took care of the issue


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## BlizzardBeater (Aug 29, 2010)

Is it dropping out of torque converter lock up or is it dropping out of gear?


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## mudduck72 (Apr 4, 2012)

I assume torque lock up


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## BlizzardBeater (Aug 29, 2010)

Isnt that normal operation? As far as I can remember, all my chevy trannies with lock up have done that.


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