4l80e lost forward after being parked for months

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JavaMan

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I got a 96 K2500 Suburban 145k miles, no forward movement, but can reverse. Worked great prior to being parked for months.

So first a little history. Trans fluid was changed at 62k miles, medium darkness, then changed again at 114k miles, medium darkness. We started a vacation a few days later, it started having some "slipping" in OD which would cause OD to lockout and shift hard, also gave transmission slipping code, P1870 I think. Putting the selector in 3rd I was able to complete our vacation trip. When we got back, I decided to drain the Valvoline MaxLife, and put in Dexron 3. That got it back to normal again.
Around 125k miles, it started the "slipping" in OD which would cause OD to lockout. The fluid still looked bright. I avoided the issue by just putting the selector in 3rd all the time. Around 128k miles started getting "slipping" in 3rd also.
Took it to a trans shop, at 130k. He used his tool to command each gear while I was driving. He stated it was not slipping, but dropping to second gear. We confirmed by getting it up to 70, letting it slip then it grabbed at 65, same RPM at that speed when 2nd was commanded. So he replaced all the solenoids and ended up doing a valve body rebuild while he had it apart because there were some other issues in there. Was driving great after that.
Last summer we did a trip cross country, about 8k miles, and no problems with it. It got parked in August with 145k miles, wasn't driven again till November, was acting a bit weird. Sluggish to shift. The fluid was slightly dark, a tad low, so I topped it off. Wasn't started again till last week, five months parked, I know not a great thing. It won't go forward now, reverse seems to work, though I can't back up far. I pushed it forward and backed it up again. Still no forward. Let it warm up for about 10 minutes, still no forward. The fluid still looks good, it's the right level, though I don't know if the trans was at operating temperature, but the engine was.
Any ideas on what to do? Did I break something by leaving it parked for too long?
 

stutaeng

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Sounds like a damaged forward drum/clutch?
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Hard to say without opening it up and inspecting everything. Leaving it parked for that long "should't" have been the problem, by itself...(I've got a 04 suburban also with an 4L80e that's been sitting for over a year, and it's okay. But I start it up and let it reach operating temperature at least monthly) more likely you already had some partial internal issue. The valve body work took care of some of the issues, but ultimately some gasket or sealing ring failed internally. I'm just guessing here...

Here's a good source of information and diagnostics: https://shop.ukrtrans.biz/wp-content/uploads/catalogs/4L80E.pdf
 
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