4L80E - Please give me your expert opinion

[tinknocker]

1998 K3500 - 4L80E
Fluid was light brown. Shifting was ok but lost OD sometimes and a cpl times had limp mode. Reverse had a shudder and slip but works.

Changes fluid to the good stuff and filter, etc. Cleaned the sump - fine dust like graphite sludge, like a thin coating over the inside of the pan.

Truck shifts good now. Reverse is still a problem.

Thank you.
PS Because of the service the fluid looks better but the torque converter (6 qts. of so) has contaminated the good stuff. No power purge for me as it might screw up the works completely.

 

[docdray]

drain then refill with a short run in between- do this process 3 times, should get a good percentage change. or unhook tranny cooler line and dump it in a bucket while filling -lets the pump change the fluid(method I use).

 

[4wdaaron]

What do you mean by "limp mode"? My 2000 shifts real hard sometimes after it can't decide to stay in or out of OD.

 

[tinknocker]

Limp Mode is a protective measure brought on by the ECM to protect the tranny. You will only have 1st and 2nd and be able to limp home. I am not sure as to if I had a true limp mode of if it was something else. I check codes and the only ones were from the Elec. IP missing. I am sure I am looking at hardware, not the ECM, but a standard "Limp Mode" can be experienced when a loose battery cable is breaking the ECM's elec. supply. It can also be something more significant that would represent harm to the tranny.

 

[tinknocker]

I checked codes and had P0756
P0717 along with the IP codes because of the conversion. I removed the input sensor in tranny and cleaned it. It loked good so I put it back in. I changed the pan fluid two times and removed my "fooler" and restored the ECM wires and bingo - runs great. Reverse is on a separate clutch - it works better too!

 

[tinknocker]

Limp mode did come back. I pulled the speed sensor from the trans case and it looked good. After researching the P0756, I realized the problem was probably in the case. Every incident of L Mode, I would pull over and most times, I would get 3rd and 4th back. A sensor must be sending info to the ECM and causing L Mode.

The info on P0756 is from a Cadillac site but I think it is pertinent:
If the vehicle shows trouble code P0756, it’s a sign of a mechanical failure, not a problem an electrical connector. GM says that a small orifice on the top of the spacer plate can get clogged with debris and cause this trouble code. The repair involves removing the valve body spacer plate and inspecting orifice #29. The code can also be caused by a cracked, broken, or leaking 2-3 shift solenoid. A stuck or hung-up 2-3 shift valve could also bring up this code. If the vehicle is still in warranty, it will be covered. Otherwise, you will have to discuss the cost of repair with your dealer to see if GM is willing to pay for it as a goodwill gesture.

Debris? Could be since my fluid was ugly before I started dumping pan fluid to clean it out.

I went to Autozone and picked up some Sea Foam Tranny Tune/Flush and wow! No limp mode for almost 200 miles. It did something! Anyway, I went home and dumped fluid and put in another pint of Sea Foam. I went for a drive and L Mode again! I chalked it up to the Sea Foam not getting mixed in yet because I put it in first. I started it back up and no more L Mode for 75 miles. Sea Foam works!

 

[jcool]

Limp mode did come back. I pulled the speed sensor from the trans case and it looked good. After researching the P0756, I realized the problem was probably in the case. Every incident of L Mode, I would pull over and most times, I would get 3rd and 4th back. A sensor must be sending info to the ECM and causing L Mode.

The info on P0756 is from a Cadillac site but I think it is pertinent:
If the vehicle shows trouble code P0756, it’s a sign of a mechanical failure, not a problem an electrical connector. GM says that a small orifice on the top of the spacer plate can get clogged with debris and cause this trouble code. The repair involves removing the valve body spacer plate and inspecting orifice #29. The code can also be caused by a cracked, broken, or leaking 2-3 shift solenoid. A stuck or hung-up 2-3 shift valve could also bring up this code. If the vehicle is still in warranty, it will be covered. Otherwise, you will have to discuss the cost of repair with your dealer to see if GM is willing to pay for it as a goodwill gesture.

Debris? Could be since my fluid was ugly before I started dumping pan fluid to clean it out.

I went to Autozone and picked up some Sea Foam Tranny Tune/Flush and wow! No limp mode for almost 200 miles. It did something! Anyway, I went home and dumped fluid and put in another pint of Sea Foam. I went for a drive and L Mode again! I chalked it up to the Sea Foam not getting mixed in yet because I put it in first. I started it back up and no more L Mode for 75 miles. Sea Foam works!

may just be a bandaid though, change the fluid a few more times and hopefully nothing is damaged

 

[tinknocker]

It was - Game over - getting it replaced!

 

[saratoga]

Uh-oh. Let us know how it works out.

 

[tinknocker]

I am picking up a used tranny as Jaspers are too expensive and after my transfer case fiasco (4 trans cases till it was right), I think a used one will be better. I was able to eliminate my limp mode completely when I unhooked my TPS. Remember, this is the truck with the mechanical IP http://www.dieselplace.com/forum/showthread.php?t=285327. I think the TPS needs to be set just right but with the degrading situation with the tranny, it was hard to tell what was going on. When I get the tranny right, I will continue to tweek this thing and contribute to the information base and welcome input. Thanks - Bob

 

[tinknocker]

I got the Jasper. Now I have the trans and the transfer (4th one under warranty) and the rear in this truck, so I guess the drive train is Ok for now. My 98 has been problems since I got it. This lil dump would be gone if it was not a dump. Now I going to fix it up with new seats, grill, paint, etc.

Talk soon,
Bob
_______

 

[jcool]

I got the Jasper. Now I have the trans and the transfer (4th one under warranty) and the rear in this truck, so I guess the drive train is Ok for now. My 98 has been problems since I got it. This lil dump would be gone if it was not a dump. Now I going to fix it up with new seats, grill, paint, etc.

Talk soon,
Bob
_______

awesome! I know you feel you just spent a lot of money on her, which you did. but look at it like this man, you now have all them parts under warranty and were rebuilt to oem specs. so to be honest if your keeping the truck for 3 years at least you just made a very good investment in it! just my 2 cents :smile5: