4L80 Rebuild Barely Moves Help

[sanfriz]

This was my first automatic rebuild. I watched hours of videos and I think it went together right but now it will barely move. 60 PSI at idle is all positions other than reverse and it jumps to 100ish. Does increase with throttle. I really want to know what I did wrong and its hard to find much. I have 2 codes, P0710 AND P2761 but mostly everything I read about them is a voltage issue but wont stop it from driving. I am pulling the plug tomorrow to see if that helps. Rebuild included a remanufactured valve body and new reverse servo. If I'm not looking hard enough on how to use this data to troubleshoot, please let me know. I genuinely want to figure the out and not be handed the answer. I uploaded my last data log from today if that helps. Has a new 2200-2400 stall converter. 20230817 Trans Test.hpl

[TransGo Robert]

Looking at the limited transmission PIDs in your log it seems like it is binding up since the input speed drops to zero. Does it feel like neutral or like the brakes are on? Will it pull in manual low range?

[sanfriz]

It feels like neutral. It will rock a little around 1800 rpm. It doesn't make any bad sounds. I found another person with similar issues but theirs worked with the electrical unplugged, I just tried that, and it would not move at all. Is there any change my converter pulled away because there was too much of a gap? I honestly didn't, measure, just eye balled it. I read though that if there would be no input shaft speed if the converter wasn't seated correctly.

It does feel like it moves easier, at less RPM, in 2nd and 3rd. Can't reach first.

I ordered GM4L80E Transmissions: How to Rebuild & Modify (The Workbench How-to, 499) so I'm prepared to pull it and go through it again. Just a little disheartening it isn't working after putting so many hours into it.

[blindsquirrel]

If it doesn't default to 2nd gear with the 20-way unplugged, it cannot be either electrical or tune-related. It can only be something inside the trans.

[RDF1]

I would double check the OD sprag.

[blindsquirrel]

https://forum.hptuners.com/showthrea...-forward-gears

[sanfriz]

Thanks for the replies. I'm pulling it back out tonight 😔 I'll try 1 more time before taking it to a builder.

[TransGo Robert]

It feels like neutral. It will rock a little around 1800 rpm. It doesn't make any bad sounds. I found another person with similar issues but theirs worked with the electrical unplugged, I just tried that, and it would not move at all. Is there any change my converter pulled away because there was too much of a gap? I honestly didn't, measure, just eye balled it. I read though that if there would be no input shaft speed if the converter wasn't seated correctly.

It does feel like it moves easier, at less RPM, in 2nd and 3rd. Can't reach first.

I ordered GM4L80E Transmissions: How to Rebuild & Modify (The Workbench How-to, 499) so I'm prepared to pull it and go through it again. Just a little disheartening it isn't working after putting so many hours into it.

Ok then your forward drum does not make a solid connection with the splines in the converter. Wrong converter, stripped splines in converter, or something like that. It has to come back out.

[kingtal0n]

Do you have a copy of the 4l80e service manual?


If not PM me I can get you a copy

[sanfriz]

Ok then your forward drum does not make a solid connection with the splines in the converter. Wrong converter, stripped splines in converter, or something like that. It has to come back out.

It is a cheaper 2400 eBay converter but the 4L80 page on facebook said it was ok? I am questioning if all the clutch packs set in right. I thought I felt them bottom out but I was lazy, and rushed, and didn't use air to verify they engaged. Going to fast is normally my setback so why change what doesn't always work

[sanfriz]

Turns out it was my overrun spring not being seated properly. I had the snap ring under the roller clutch instead of its slot. So there was no pressure on the piston. I had to replace the piston and the clutch disks but everything else looked ok. I can't road test but its moving around my house so that's definitely a step in the right direction.

[TransGo Robert]

Turns out it was my overrun spring not being seated properly. I had the snap ring under the roller clutch instead of its slot. So there was no pressure on the piston. I had to replace the piston and the clutch disks but everything else looked ok. I can't road test but its moving around my house so that's definitely a step in the right direction.

Glad you found the problem, thanks for taking the time to post the fix.