6L80 TC not locking up after rebuild

[weskoerber]

Hi all, first post here. I couldn't find any first post guidelines so I hope I'm doing this right... Hoping to get some input from y'all who are much smarter than me!

I just finished rebuilding my 6L80 after a converter failure tore up my old pump at ~130k. I used a CDT level 2 rebuild kit, CTS-V 6L90 TC, zip kit, new pump cover and bell housing, etc. After rebuilding I reset adapts and tuned using Bluecat Trans tool and disabled TCC apply in 1-3. I also added 10% to the TCC apply ramp. It's shifting alright so far but it doesn't look like the TCC is locking.

I took it for a test drive and was monitoring my TCC slip rpm and TCC line pressure. I could see TCC line pressure increase but it didn't seem to have an effect on TCC slip. Here's a screenshot of what I was seeing:

Screenshot from 2024-01-14 19-44-16.png

At the end of my test drive as I was driving up the hill to my house the check engine light came on. I read it with VCM Scanner and it was "P0741 Torque Converter Clutch Solenoid Circuit Performance/Stuck Off." I cleared it and went on another test drive to see if it would come back on but it hasn't (yet). I didn't have this issue before hand, so I'm not sure why it's happening now.

I checked line pressure at idle in park and read 90 PSI, so my initial feeling is that the pump is producing enough pressure but the TCC solenoid is bad. My understanding is that the TCC line pressure reading in VCM Scanner isn't a reading of the actual line pressure, it's the expected line pressure based on the duty cycle of the TCC apply. Is that accurate or a load of crap?

I'm afraid to drive it because if the TCC is slipping, I'm going to tear up my pump and I'll be right back at square 1. But if it's a bad solenoid it won't apply at all, so no harm no foul. In either case, could I just disable TCC apply across the board and safely drive it around without lockup? I don't want to ignore this issue so I need to get to the bottom of this, but I'm wondering if there's anything I can do in the short term to allow me to drive around without damaging anything.

What steps should I take to diagnose no TCC apply? Has anyone run into this issue or know what's up?

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Edits:

2024-01-15: I added the log file I took the screenshot from. I couldn't attach it to this post, the file upload wasn't working, so here's a link to it on my Google Drive: https://drive.google.com/file/d/1DQg...hiqIJaSe3/view.

[GHuggins]

Did you put the Oring on the input shaft before installing the converter? It's one of the things that seals the converter for clutch apply.

[weskoerber]

Did you put the Oring on the input shaft before installing the converter? It's one of the things that seals the converter for clutch apply.

Yessir, I did.

[hjtrbo]

Disabling lock in all gears is a good idea. The pressure reading in the scanner is commanded solenoid pressure.

[TransGo Robert]

You have no lock-up at all looking at your screenshot. A log would be better of course but it seems pretty straight forward. The number one suspect the the TCC control valve in the pump just because it is fairly common for it to stick. Unfortunately the transmission has to come out for that. The next possibility is the TCC regulator valve in the valve body being stuck. That is far less common, but at least you don't have to pull it. Next would be a bad solenoid but I really doubt it, they rarely fail and it did not do that until you worked on it. Of course you could have also got a defective converter. As for driving without lock-up it is ok for shirt drive but not for long drive in overdriven ratios. The heat generated out of lock-up in an overdriven ratio is tremendous, you will overheat the unit.