4l80e shifting out of overdrive

[upper_tanker]

My dad has a 1997 K2500 5.7/80E, uses it mainly as a plow truck but takes really good care of it, it's his pride and joy. It has had an issue for this and last winter where you'll just be driving it and it will shift out of overdrive into 3rd. It seems like there is nothing obvious causing this. It doesn't happen when you hit bumps, and when it does happen, it's not going up a hill. Your foot's just on the gas cruising and it will shift down. He's been complaining to me about this for a while. I finally got to drive the truck a few times and see what he was talking about.

The first time I experienced it was a few weeks ago. I was taking a load of tires (off the rim, not heavy) about 6 miles away. I warmed the truck up in our shop, made it all the way there, and then it did it when I was halfway back. Just driving, foot steady on the gas, and it shifted down. I tried to feather the gas a bit to see if it would shift back up into OD but it didn't. I also tried moving the gear shift lever to 3 and then back up to OD, nothing. I just went on another trip to drop another load of tires off today and it did it pretty close to the same area. Made it all the way there, and halfway back it did it. When it does shift into OD, all shifts are nice and smooth/firm. When the OD issue happens, the 1-2 and 2-3 shifts are neck breakers.

The trans was rebuilt probably 3-4 years ago by the same shop who rebuilds all of our transmissions. They (at least used to do) nice jobs and we've never had any issues. We took it to them before last winter to check it out and I think they put a solenoid in but I can't remember. I want to ask if anybody knows of anything that I can check here before we take it back to them. It's out of warranty now obviously so whatever the issue is, he will have to pay for it. Just curious to see if anybody else is having this issue or knows what I can check.

I have checked the cab mounts and trans/engine mounts, they're all good. Engine and trans mounts were new when the reman engine was put in 8k ago, and the trans mounts were new when they rebuilt it 6kish ago. I don't see any oil in the trans plug, and it seems like the shift cable is nice and smooth with no binding. I do know I put a new cable in it probably 2-3 years ago.

Anyone have any ideas?

 

[yevgenievich]

Tcc slip issue can force drop to 3rd and high pressures as ecu tries to bring pressures up for lock up to hold. Can be a wore bore in the valve body, or oring or torque converter as more common issues

 

[upper_tanker]

Tcc slip issue can force drop to 3rd and high pressures as ecu tries to bring pressures up for lock up to hold. Can be a wore bore in the valve body, or oring or torque converter as more common issues

You know.. at the risk of sounding like an idiot when I first posted, I thought this could be converter related. ONLY because ever since the trans was rebuilt, it has had almost like a hesitation off the go. Like it just doesn't move like it should until 2000-2500 RPM. It's so weird because I wasn't even driving it hard when it did it both times. I appreciate the input.

We can probably swap the TC out, he has a few lifts. Any idea on a good recommendation? Again, it's used as a plow truck so I have no idea what he'd even want as far as stall. I guess the price would depend on if it'd be worth the gamble. Or maybe we should just take it back to the trans shop. lol

 

[yevgenievich]

You know.. at the risk of sounding like an idiot when I first posted, I thought this could be converter related. ONLY because ever since the trans was rebuilt, it has had almost like a hesitation off the go. Like it just doesn't move like it should until 2000-2500 RPM. It's so weird because I wasn't even driving it hard when it did it both times. I appreciate the input.

We can probably swap the TC out, he has a few lifts. Any idea on a good recommendation? Again, it's used as a plow truck so I have no idea what he'd even want as far as stall. I guess the price would depend on if it'd be worth the gamble. Or maybe we should just take it back to the trans shop. lol

I would just take it to the trans shop if an option(if have warranty). I am running cheap rebuilt converter from autozone in my burban and it seem to work ok. Have a custom converter in the other truck from the converter shop in dallas(texas converters I believe). Valve body should be checked as well.

 

[Schurkey]

My dad has a 1997 K2500 5.7/80E... ...you'll just be driving it and it will shift out of overdrive into 3rd.

Is this REALLY a "shift" from OD to direct drive (3rd gear), or is this the loss of the torque converter clutch while still in OD? Or both--from OD and the converter clutch locked, to 3rd gear, TCC unlocked?

When the downshift/loss of TCC happens, the other shifts get harsh? You need to connect a scan tool and find out what the computer is trying to tell you. There are probably "codes", but as always the real info is in the data stream.

This is probably some kind of "safety" reaction of the computer, trying to not burn up the trans due to some occasional fault that comes and goes--mostly when the trans is completely warmed-up.

How old (years/mileage) is the fluid and filter? Is the fluid level correct? Does the engine misfire?

 

[udidwht]

In stock form the 4L80E with a large enough load won't hold OD. Seems to be par for the course with the trans unless one pulls the trans and upgrades at min to a better TC. I have a stock one in my RV and even the slightest hill or headwind will put it into third. Nice flat highway and no winds and works great back to OD. But it is back & forth due to the weight of the coach ~11,000lb unladen. One is in essence 'always towing' with these RVs even when you're not towing such as I. I always thought is was a bit of an oxymoron in these early year class A RVs to put overdrive in it only to have it go into 3rd often.

What RPMs you seeing in 3rd?