4L80e lost overdrive

[Keitha]

Last night my 4L80e lost overdrive with absolutely no warning. Just cruising along at about 50mph. As I gave it a bit of throttle, I felt it slip and it dropped down to 3rd gear. If I shut the motor off it will "reset" and work for a bit until it slips again, then no overdrive. I dropped the pan this morning and there was some sludge on the pan magnet. I took it to OC Transmissions in Costa Mesa and his scanner confirmed my fears. I need a rebuild.
There goes the $2,000 I was saving for some AFR Heads.
Anybody have anything good or bad to say about OC Transmissions (on Logan - near Fairview and Baker)? I still have my Suburban but plan to drop it off with him this week.

 

[sweetk30]

should be a code in the computer for slipage or solinoid problems. i would do more reserch first. and how many miles you got on it ? what year is it ? need more info. and if you had a smoked tranny you would more than likly have a ton of clutch material in the pan and brown or black fluid. but this is not always the case.

 

[Fordum]

Not real familiar with this tranny, but having a scan tool show it needs a rebuild sounds a little off.
I mean, a scan tool shows error codes, and can activate different units, but I don't think it has a "burnt up" error code.

Of course, I was not there, and it may be that he commanded it to od, and it did not pull.
From which he could infer that the clutch was bad. But, it could just as easy be a bad actuator or bad connection.

It sounds like the computer commanded od, saw slippage and dropped back into 3ard.
But there is a lot of less expensive parts between the computer and the od clutch that can cause that.

I would get a 2and opinion. And this might just be the best place to get it. Wait until a few others have chimed in. There are guys here that know a heck of a lot more than I do, and probably more than the OC guys do too.

J.

 

[sweetk30]

yes the 4l80-e has 2 speed sensors in it system. it reads input rpm to the tranny and then reads the output rpm from the tranny. this then tells the tranny if there is a slipage problem going on. also there will be solinoids to switch the flow of fluid from port to port. so if you have a bad solinoid this can cause a problem.

and if this is your 91 listed in your info then who knows if it ever had the wire harnness update req for 91-93 4l80-e trannys for wiring problems in the tranny valve body area.

 

[Keitha]

SweetK30 is right on. I was able to pull DTC 68 which only tells you that it is an overdrive error. When I pulled the pan this morning there was a decent amount of metalic sludge on the pan magnet but the fluid was not too bad. The scan tool he used is the GM Tech 1 and it showed slippage in 4th.
If you shut the engine off and restart, the tranny acts normal and will go to OD and lock the converter. If you give it a bit of gas or hit a hill and try to hold speed, you can feel it slip and then drop to 3rd. It will not go back into OD until you shut it off and restart.
The tranny has been with me for a while. It does have the updated wire harness.
http://octrans.net/ This is the shop. They have a pretty good reputation around here and have been at it for a long time.
I will not be bringing it in until Wednesday, so I will keep my eyes on this board for any good info.

thanks all,

 

[sweetk30]

o.k. thats better. he used a good scanner.

and wont hold on heavy loads slipage problem. o.k. might just need to pull it and check over.

but i would like you said keep checking. dont forget to search pirate4x4 tons of good hard core tech overthere. but have a flame suit on if you ask a stupid noob question.

 

[Thunder]

It may be your 3-4 shift solenoid. Or possibly the pressure switch
A little sludge in the pan is no big deal. as long as there are no chunks and metal pieces.
Its common for the 3-4 solenoid to go out. usually give you problems after the tranny is warmed up
tranny shops love it ..Sell the person a full rebuild for big bucks wnen you only need a 40.00 part.

drop the pan and replace both 1-2 and 3-4 solenoids and pressure switch. cost around 140 including the fluid filter. Your trans will seem like new.
would not hurt to put in a new TCC lock up solenoid/valve while you are in there too. The O ring in the valve goes bad and it wil leak pressure causing some slip.

Dont know what year your truck is but on TBI trucks a MAP sensor going bad will also cause it to drop out of overdrive. it will usulaay not throw a MAP code untill the sensor gets totally out of wack.

 

[sweetk30]

in his profile its a 91 3/4 ton burb.

 

[Keitha]

I will defenetly check on the solenoids. Thanks for the tip.

 

[blazindorito]

I have a 4l80e with transfercase for sale. It came out of a running burb w/ less than 100,000 miles.

$700 and will deliver to Costa MEsa

Let me know
Ernie

 

[Keitha]

OK, I talked with another tranny guy and got the following story:
The 4L80e use 2 solenoids to controll all the shifting. 1st gear is solenoid "A" on, 2nd is both off, 3rd is "B" on, and OD is both on. If there were a bad solenoid I would also have problems in 1st or 3rd gear, but not just OD alone.
The guy at Orange County transmissions said the exact same thing.
1st colomn is "A", 2nd colomn is "B", 3rd is TCC.

 

[cuervo]

There is also a manifold perssure switch but I think it's a code in the 30s 36 or 37 I think. It's been a while since I went through my code issues.