4l80E falls out of 4th
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4l80E falls out of 4th I'm working on a 1998 4L80E transmission. It was just rebuilt with all new frictions, steels, and convertor. It shifts normally from 1st to 3rd, the convertor locks up, then it neutrals when trying to shift into 4th. If you rev the engine there's nothing there, you have to pull the shifter into 3 to re-engage third. I reamed the AFL bore and installed a new Transgo valve, also replaced the shift valve springs with the Sonnax 34944-02K kit. No change. Tried another valve body, reamed and installed the AFL and springs into that one and I still have the exact same problem. Next I removed the transmission and tore it down again. I air tested all of the drums and they are all holding pressure; the sprags are also holding. No leaks between the drums and sealing rings either. Thinking there may be a crack in the case I reassembled everything into another case. Same problem. It will sometimes shift into fourth but immediately falls out and neutrals. No diagnostic codes either. I've tried commanding 4th with my scanner and same result, it just neutrals.
At this point I don't know what to do anymore. I've built tons of these things over the years and have never ran into anything like this.
At this point I don't know what to do anymore. I've built tons of these things over the years and have never ran into anything like this.
I'm working on a 1998 4L80E transmission. It was just rebuilt with all new frictions, steels, and convertor. It shifts normally from 1st to 3rd, the convertor locks up, then it neutrals when trying to shift into 4th. If you rev the engine there's nothing there, you have to pull the shifter into 3 to re-engage third. I reamed the AFL bore and installed a new Transgo valve, also replaced the shift valve springs with the Sonnax 34944-02K kit. No change. Tried another valve body, reamed and installed the AFL and springs into that one and I still have the exact same problem. Next I removed the transmission and tore it down again. I air tested all of the drums and they are all holding pressure; the sprags are also holding. No leaks between the drums and sealing rings either. Thinking there may be a crack in the case I reassembled everything into another case. Same problem. It will sometimes shift into fourth but immediately falls out and neutrals. No diagnostic codes either. I've tried commanding 4th with my scanner and same result, it just neutrals.
At this point I don't know what to do anymore. I've built tons of these things over the years and have never ran into anything like this.
At this point I don't know what to do anymore. I've built tons of these things over the years and have never ran into anything like this.
Go over your VB assembly.
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You're right, it was dropping back into 1st. I didn't realize it until I wound the engine up to about 4,000 rpm and it started accelerating again. I pulled the valve body back off and went through it again but could not find anything wrong. Ran my air tests on the drums again and everything is holding. I found another unmolested valve body that I cleaned and inspected, then installed without making any mods. Same thing. Also swapped the solenoids with no change. The PCM is commanding 4th and I can do the same with my scan tool but it falls out after a second or two. I've spoken over the phone with several different builders and they're clueless.
I'm about ready to give up on it and find another core to build. I've wasted over three days fighting with this thing and I'm getting nowhere.
I'm about ready to give up on it and find another core to build. I've wasted over three days fighting with this thing and I'm getting nowhere.
Last edited by cdo; Feb 14, 2020 at 07:51 AM.
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From: Iowa
What does it have for a transmission controller?
1st gear is A/B ON/OFF
4th is A/B ON/ON
If the controller has a wiring issue, a circuit board issue, a tune issue, etc...that could be your problem.
With the VB Swaps, air checks, etc...seems like I would start looking at the controller.
1st gear is A/B ON/OFF
4th is A/B ON/ON
If the controller has a wiring issue, a circuit board issue, a tune issue, etc...that could be your problem.
With the VB Swaps, air checks, etc...seems like I would start looking at the controller.
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