4l80e Transmisssion Issues

cbholt · September 7, 2009

I have a 93 GMC 2500 2wd with 4L80E transmission. Running down the road in third gear or overdrive, between 2200 and 2400 RPM's, the torque converter locks and un-locks constantly. Doesn't matter if your accelerating or coasting. It will unlock for about a second and then lock back up. and then about 3 seconds later do it again. The computer does NOT throw any codes. Nobody locally seems to be able to figure this out. The Transmission has been rebuilt 5000 miles ago and the Torque Converter Clutch was replaced twice. The assumption I am making is that it is the Torque converter unlocking, and not the transmission slipping. When it unlocks, the rpm's jump about 300 rpms. But it is possible im wrong. Any help would be appreciated.

Please excuse the earlier posting that said 4L60E. I can't delete or change it.

wog2006 · September 11, 2009

I am not a technician! I wanted to tell you what happened to my 96 c2500 5.7/4l80e.

I was driving to work and it would not shift out of 2nd. Figured it was going to grenade.

Tranny-meister checked and fluid was perfect and no particles in pan.

Changed tps, filter, fluid anyway. It jumped out of overdrive a few times on the highway, but would not go back in, even after slowing down. My other mechanic suggested the computer was causing tranny shift issues. I gave in a few weeks later and got a new "brain". It fixed it.

There were no codes or lights during this time.

Good luck!

oldschool327 · September 11, 2009

I posted this on your same question in the Ask the GM tech forum;

Ok, you have a few things to check first before assuming the tranny is the problem.

The 4L80E gets information from various sensors to set clutch lockup and shift points. The two main items are the TPS and its adjustment, and the Crank angle sensor. These tell your TCM What position your throttle is at and how fast the engine is spinning. I just verified again in the Hydromatic book. This is where you should start. The TPS has a very narrow range of voltage adjustment that it needs to fall in and can only be measured with a go/no go throttle block and multimeter (or a fancy GM machine). Not even the Super Shifter or Tech II can do this. Then make sure the pins on the Crank sensor have the proper voltage and ohms.

After those are verified you could take out the input and output speed sensors from the driver side of the tranny and clean them with electrical or brake cleaner. There is a small magnetic nipple that build up metal flakes and rust over time. They have to be spotless for a good reading. Also has the Force Shift Motor been looked at?

This could be all kinds of item but those are the most suspect. Even your brake switch is wired into the TCM. Start with the above and if you still have problems I will upload the 4L80E manual for you to go through. It is big so it will take a bit.

I have been working on that tranny (my favorite) for 12 years now and it is very rare to burn one out after 5000 miles. Dont think I have ever seen an 80 go that early, so That is why i believe it is electrical, more on the motor side than the tranny.

Brian

keckjr · September 13, 2009

If none of the above works for you and the problem still isnt found ive seen a couple converters that would do that exact same thing. Apparently they had the ground wire coming from the tcc to the ecm rub through the insulation and was grounding out making the converter lock and unlock constantly. It was because of a shabby installation and wire routing but nonetheless if none of the above works it might make you some helpful info.

Nytemare · September 13, 2009

I would suggest having a look at your lockup solenoid (TCC)...that's where I would start.

sbgalaxie · February 24, 2010

I posted this on your same question in the Ask the GM tech forum;

Ok, you have a few things to check first before assuming the tranny is the problem.

The 4L80E gets information from various sensors to set clutch lockup and shift points. The two main items are the TPS and its adjustment, and the Crank angle sensor. These tell your TCM What position your throttle is at and how fast the engine is spinning. I just verified again in the Hydromatic book. This is where you should start. The TPS has a very narrow range of voltage adjustment that it needs to fall in and can only be measured with a go/no go throttle block and multimeter (or a fancy GM machine). Not even the Super Shifter or Tech II can do this. Then make sure the pins on the Crank sensor have the proper voltage and ohms.

After those are verified you could take out the input and output speed sensors from the driver side of the tranny and clean them with electrical or brake cleaner. There is a small magnetic nipple that build up metal flakes and rust over time. They have to be spotless for a good reading. Also has the Force Shift Motor been looked at?

This could be all kinds of item but those are the most suspect. Even your brake switch is wired into the TCM. Start with the above and if you still have problems I will upload the 4L80E manual for you to go through. It is big so it will take a bit.

I have been working on that tranny (my favorite) for 12 years now and it is very rare to burn one out after 5000 miles. Dont think I have ever seen an 80 go that early, so That is why i believe it is electrical, more on the motor side than the tranny.

Brian

This is great information. I'm having a very similar issue at 150K on my '96 C3500. No one here seems to be able to tell me what's wrong, and not code is present. While driving hooked up to a scanner, my buddy noted the TCC Slip value. It was running about 8 or 9 while cruising at 70 MPH, but during the slips, it would bounce. He saw it a 150 for a brief second. As I'm driving, I notice the litte slips and the converter locking and unlocking. Twice now, the transmission seems to have gone into neutral, once while accelerating from a stop, and once while in cruise control. While in cruise, the transmission felt like it let go, and I noticed a flash of the ABS warning light.

I'm going to go check the speed sensors, but I'll have to call on professionals to check the TPS. The crank sensor was replaced last year, but no other issues seem to have arisen from that.

Any additional thoughts would be appreciated. It's a great truck I've had for 14 years, but I have to watch my $$$.