97' 4l80E problems

[Frisby454]

Hey folks I rarely ever turn to forums on the Internet for mechanical help but I am baffled...

I have a 97' gmc k2500 with around 167k miles on her and the transmission is acting up. Less than 5k miles on the transmission after a rebuild and I am experiencing intermittent slipping into first and limp mode haunts me every so often. Used to only slip a couple of times in the morning then went into limp mode once or twice a week in the mornings and now slipping throughout the day and stuck in second. If I pull over to the side of the road and shut the thing off for a couple of seconds it'll work fine again. Took it into a shop because of the warranty and they told me i needed an ignition switch. Replaced that and ignition lock cylinder and problems keep happening. Any help would be greatly appreciated!

 

[Schurkey]

I'd go back to the folks who diagnosed the ignition switch, and tell them that replacing it didn't help. Time for them to step-up.

Failing that, connect a scan tool, find out why it's going into Limp mode. Verify your various sensors--trans and engine. Look at the shift adaptions, see if they're reasonable.

Assure it's full of fluid, AND the fluid is in good condition.

Wouldn't surprise me to find that the computer knows the trans is slipping, and that's why it's forced into Limp mode.

 

[NickTransmissions]

Hey folks I rarely ever turn to forums on the Internet for mechanical help but I am baffled...

I have a 97' gmc k2500 with around 167k miles on her and the transmission is acting up. Less than 5k miles on the transmission after a rebuild and I am experiencing intermittent slipping into first and limp mode haunts me every so often. Used to only slip a couple of times in the morning then went into limp mode once or twice a week in the mornings and now slipping throughout the day and stuck in second. If I pull over to the side of the road and shut the thing off for a couple of seconds it'll work fine again. Took it into a shop because of the warranty and they told me i needed an ignition switch. Replaced that and ignition lock cylinder and problems keep happening. Any help would be greatly appreciated!

Slipping in forward (first gear) tells me they probably didnt check for wear in the forward drum where the input shaft sealing rings for the forward drum sit. That bore has sealing ring groove wear like 50% of the time, esp on units with 150k or more miles. I always ream and sleeve them with billet steel or ductile iron inserts so that problem doesn't happen again. Your ignition switch problems wouldnt cause slips in forward gear, that's either drum wear or they didnt resize the teflon rings correctly upon installation and one or both got nicled up and now it's torn enough to allow apply fluid for the forward clutch to blow by.

Here's the input shaft with the two pairs of sealing rings being resized after installation onto the shaft - the fwd drum uses the smaller pair on the right).

You must be registered for see images attach

ETA: Questions for that shop who did the rebuild - Did they replace all the electronics/electrical parts (harness, shift solenoids, epc, pressure switch manifold, speed sensors)?

What sbout the valve body - did they test or upgrade the AFL valve (its worn like 80% of the time in high mileage units - worn AFL will cause slippage if its bad enough)?

 

[Frisby454]

I'd go back to the folks who diagnosed the ignition switch, and tell them that replacing it didn't help. Time for them to step-up.

Failing that, connect a scan tool, find out why it's going into Limp mode. Verify your various sensors--trans and engine. Look at the shift adaptions, see if they're reasonable.

Assure it's full of fluid, AND the fluid is in good condition.

Wouldn't surprise me to find that the computer knows the trans is slipping, and that's why it's forced into Limp mode.

The only DTC's I get when it is in cripple mode are emissions related. I get p0141(which is a problem with my downstream O2) I just don't understand how that is related to my transmission at all.

 

[Frisby454]

Slipping in forward (first gear) tells me they probably didnt check for wear in the forward drum where the input shaft sealing rings for the forward drum sit. That bore has sealing ring groove wear like 50% of the time, esp on units with 150k or more miles. I always ream and sleeve them with billet steel or ductile iron inserts so that problem doesn't happen again. Your ignition switch problems wouldnt cause slips in forward gear, that's either drum wear or they didnt resize the teflon rings correctly upon installation and one or both got nicled up and now it's torn enough to allow apply fluid for the forward clutch to blow by.

Here's the input shaft with the two pairs of sealing rings being resized after installation onto the shaft - the fwd drum uses the smaller pair on the right).

You must be registered for see images attach

ETA: Questions for that shop who did the rebuild - Did they replace all the electronics/electrical parts (harness, shift solenoids, epc, pressure switch manifold, speed sensors)?

What sbout the valve body - did they test or upgrade the AFL valve (its worn like 80% of the time in high mileage units - worn AFL will cause slippage if its bad enough)?

I'm not sure on what they did replace because I am the second owner after the rebuild. Although, I am not sure that the problems are caused internally. Because it seems to only do it in the mornings and now evenings. And it does not consistently slip when entering first. I'm not trying to discredit what you have said because I am not an expert at all, but I just want to be 100% before i keep throwing money at it.

 

[NickTransmissions]

I'm not sure on what they did replace because I am the second owner after the rebuild. Although, I am not sure that the problems are caused internally. Because it seems to only do it in the mornings and now evenings. And it does not consistently slip when entering first. I'm not trying to discredit what you have said because I am not an expert at all, but I just want to be 100% before i keep throwing money at it.

You're slipping...right? Doesnt matter when it happens; mornings between 6-6:30, every other day at 2:25pm or only when the sun's not out. You stated in post #1:

Used to only slip a couple of times in the morning then went into limp mode once or twice a week in the mornings and now slipping throughout the day and stuck in second

Is that a true and accurate representation of your symptoms?

I'm going off what you typed so if that's not accurate or correct to your knowledge, go ahead and restate your symptoms accurately.

You have TWO problems:

1) Short/electrical problems putting the trans in limp

2) slipping, presumably in first or second (and/or other) gears.

You can fix the limp mode condition with the trans in the vehicle by chasing down, identifying and correcting the electrical problems but you're not doing anything about the cross leaks, worn sealing rings or burnt frictions until you open up the case.

You may or may not know this but when any auto trans goes into limp, the pcm or tcm maxes the line pressure, freezes all adapts as well as up/down shifts from the default limp gear which is 2nd gear for the 4L80E. If you're slipping under max line pressure, in either first or second, trans has to come out for overhaul.

I just laid out for you exactly what's happening, assuming your description of the symptoms is true and accurate to the best of your knowledge and you are slipping in first.

Fix your electrical problems so it's no longer defaulting to limp then see if it's still slipping. You may or may not have a short in either the trans internal wiring harness, one or more solenoids or both. If so, drop the pan and replace the bad electrical components...If it still slips after you've gotten it to stay out limp mode, you'll need to pull the trans out and go through it, paying very close attn to the forward drum if in fact you are slipping at all in first gear.

Good luck with it.

 

[Schurkey]

connect a scan tool, find out why it's going into Limp mode. Verify your various sensors--trans and engine. Look at the shift adaptions, see if they're reasonable.

The only DTC's I get when it is in cripple mode are emissions related. I get p0141(which is a problem with my downstream O2) I just don't understand how that is related to my transmission at all.

The scan tool does MUCH more than just read codes.

 

[DamDave]

Hey folks I rarely ever turn to forums on the Internet for mechanical help but I am baffled...

I have a 97' gmc k2500 with around 167k miles on her and the transmission is acting up. Less than 5k miles on the transmission after a rebuild and I am experiencing intermittent slipping into first and limp mode haunts me every so often. Used to only slip a couple of times in the morning then went into limp mode once or twice a week in the mornings and now slipping throughout the day and stuck in second. If I pull over to the side of the road and shut the thing off for a couple of seconds it'll work fine again. Took it into a shop because of the warranty and they told me i needed an ignition switch. Replaced that and ignition lock cylinder and problems keep happening. Any help would be greatly appreciated!

 

[DamDave]

I rarely do this either. How do I start a new post or thread or whatever the hell there called? (On a 4L80E transmission)

 

[df2x4]

I rarely do this either. How do I start a new post or thread or whatever the hell there called? (On a 4L80E transmission)

Go to whatever section you want to start a new thread in (Transmissions in this case) and there should be a button in the top right corner of the screen that says "Post Thread." Click that and you'll be taken to a page where you can type a title and body of the first post. When you're done, click "Post Thread" at the bottom.