4L80E 1st gear issues

[bigblock454]

Vehicle is a 98 6.5 Burb (mild Quadstar Tune for the past 100k miles), 200k+ miles with a considerable amount of towing during it's lifetime, been rock solid all this time but nothing lasts forever!

Started having 1-2 shift issues, under part throttle it starts to shift into 2nd, kinda half shifts then 2-3 seconds later bangs into 2nd and is fine all the way into 4th. It's not a super harsh bang but it's very noticeable. Then when coming to a stop and resuming it sometimes seems like it's in neutral, flutters in and out of gear really fast then finally finds 1st and gets moving again. Although I haven't tried it recently, when the issue first started happening it acted normal on full throttle shifts, haven't been brave enough to attempt that recently. Maintenance wise it's been treated very well and fluid currently looks good still.

Anything easy or shall I just have it completely rebuilt? Actually tempted to try this rebuild myself...

I think we have a trusted rebuilder here, but I imagine shipping to/from Indiana might kill the advantage.

 

[Wes Harden]

@Greg Ducato

Do you have a pressure gauge that you can install and read while driving. That would be 1 of the 1st steps.

 

[1-ton]

Could be your 1-2 shift solenoid.

 

[bigblock454]

Could be your 1-2 shift solenoid.

I've only ever had those up and completely fail, but I guess it's easy enough to test that. Can quality solenoids still be bought, no Chinesium? I haven't bought any in 20 years probably.

 

[1-ton]

I've only ever had those up and completely fail, but I guess it's easy enough to test that. Can quality solenoids still be bought, no Chinesium? I haven't bought any in 20 years probably.

Yes, AC/Delco shift solenoids are still available. I bought some a few years ago for my 4L80E off of a transmission supply company on the internet. If your internal wiring harness is old you might want to replace that as well while you are inside your trans. A malfunctioning internal wiring harness can cause issues as well.

 

[Greg Ducato]

Its possible that it could be a shift solenoid but solenoids control two gears so you would be having trouble with another gear as well. Sliding into second gear could be an indicator of intermediate clutch or sprag slippage. Try shifting it manually under the same throttle positions and see if it makes a difference.

 

[1-ton]

Its possible that it could be a shift solenoid but solenoids control two gears so you would be having trouble with another gear as well. Sliding into second gear could be an indicator of intermediate clutch or sprag slippage. Try shifting it manually under the same throttle positions and see if it makes a difference.

Sprags are known to be a week link on the 4L80E. When I rebuilt my 4L80E I bought some sprags from Sonnax that eliminates this week point.

 

[bigblock454]

Finally got around to swapping the shift solenoids, didn't help! Pan was clean, next to no metal on the magnet, fluid was great. Did some more full throttle tests after and it shifts nice and firm without any issues. Manual shifting with normal driving still has the issues. The kinda clunk into 2nd I suppose could be described as slipping but the 1st gear neutral situation is surely something else right? Which isn't 100% repeatable, just happens every now and then. Acts like it's in neutral when I attempt to resume, in and out of gear really fast and picks up like I neutral bombed it.

Can't find my pressure gauge, but even if it's low I guess it has to come out anyhow.

 

[bigblock454]

Also, I don't know how smart the ECM/trans communication is for this year, but no codes, at least no active codes that enable the Check Engine.

 

[1-ton]

I am not positive about this but I believe the 4 wheel indicator light is what comes on when a falt code is trigaurd for the trans.