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Discussion Starter #1
The truck is my 1993 c3500 with a 4l803 trans. I had issues with it before and I had fixed them with good results. Here is that thread.
https://www.dieselplace.com/forum/63-gm-diesel-engines/21-6-5l-diesel-engine/977648-4l80e-loses-overdrive-shifts-hard.html

Now, it is losing overdrive when it gets hot. If I let the truck cool off and restart it the problem goes away. In the morning when the truck is cold it works perfectly.

I replaced the torque converter, input speed, output speed, and throttle position sensors. That fixed my no OD problem from before. It was working great for a few thousand miles. Any suggestions are greatly appreciated.

I plan on cleaning the connector for the harness and checking my brake light switch.
 

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Is the trans not shifting into OD (4th gear)? Or is the torque convertor not locking up?
 

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Discussion Starter #3 (Edited)
Once it gets hot and I push it hard it loses OD for sure. 1-2 and 2-3 shift very hard. Like it has full line pressure. Once in 3rd, it feels a little soft, maybe not locking up in 3rd.

I should add that the torque converter is a brand new Florida torque converter, low stall. It is correct for the truck and identical to the one it replaced. When the truck is cold or not fully warm, it shifts very quick and firm. Everything feels as it should.
 

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Go on google an look up '4l80e AFL valve failure' and see if your problems match that.
 

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Codes?
 

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Might want to remove your ignition switch, open it up and check for worn corroded contacts. That will cause the exact problems you're having.
 

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Discussion Starter #7
I have a new ignition switch to replace it with once I get the time.



I have more information as far as symptoms go. I have been driving it around all week and it only acts up over 150F. When it does 1-2 shifts kind of hard but the rest are very soft, including the 3-4 shift. OD works most of the time. Only when I push it hard does OD drop out and a quick restart will fix it.



I am thinking it might be a TCC solenoid. Does these symptoms help anybody narrow it down?
 

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TCC solenoid has nothing to do with the 3-4 shift or 4th gear. It controls the clutch inside the torque converter when you are cruising so that you get better mileage. It eliminates the 'slip' of the torque converter.

How fast does your tranny heat up, and what temp does it run at when unloaded and on the highway?
 

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Discussion Starter #9 (Edited)
It runs 150 to 180 unloaded on the highway. It runs 150 to 200 while towing. It can reach around 200 in stop and go traffic on a hot day while driving it hard. It takes 10 to 15 min to reach 150 with gentle driving.


I will have the the codes read next week when I get a chance to go to my trans shop. So far I have not had a SES light come on.



Today I drove 40 miles one way and returned several hours later. It was shifting softly for most of the drive. I lost OD once on the way out when I made it downshift from 4 to 3. A rolling restart fixed the OD issue. It drives fine at 60 to 70 MPH on the back roads. If I drive it very gently it works decently, which is why I am still driving it.
 

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Discussion Starter #10
I went to my trans mechanic earlier in the week. He hooked up the scan tool and we went for a test drive. His assessment is that the solenoids are working and when a gear is called for by the computer the trans has a delay before shifting. He thinks it could be debris plugging up holes on the valve body plate. I think this makes sense because a few thousand miles earlier I had a torque converter fail and this put metal flakes in the pan.

I am going to have him pull the valve body and service it. Hopefully the problem can by fixed without pulling the trans.
 

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Sounds reasonable. Let us know what happens.
 

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Discussion Starter #12
The verdict is in. It is a broken 3rd gear thrust washer. It has disintegrated and blocked up the holes in the valve body. The fix is a total rebuild or drop in a used trans. Looks like I am going to upgrade the truck to work with a 96 4l80e. I found a used one for 275 vs 1100 for a total rebuild. I am going to go used and save up to have the old one rebuilt. This way I can get back on the road now and have a spare built up for later.

My options are 275 for a working used 4l80e or 650 for a used 4l80e from a salvage yard with a 90 day warranty. Which one would you choose?
 

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I'd hit up local junkyards, and individuals parting out their trucks on craigslist.


Of the two you mention, I'd go with the cheaper one.
 

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If you put a 96 in a 93 you will have to use your old force motor. DO NOT use the one that is in the 96. Once you get it in if it isn't acting right you will need to put the VB and separator plate from the 93 in the 96. I had a 94.


I bought for the hard parts. When the trans shop rebuilt it I had hell. I told the GM that after it burned up that this was there last change before we let a Judge figure it out. They rebuilt it same crap. The owner got involved and had me bring the old VB and plate. They had the 94 plate in the trans. Guessing they had the 93 VB in it.



This is from one of my post: 94 and up trannys were built with this new force motor,new spacer plate, and the elimination of the torque signal compensator valve inthe accumulator housing. These parts are not backwards compatible with the 91 –93 trannys. You can’t reprogram the TCM to accommodate the 614 Hz force motor. Youneed to install the correct force motor for your tranny. DO NOT drive until done. 91 – 93 trannys forcemotor OEM part number is 8677314


Here is the parts upgrades: https://www.dieselplace.com/forum/63-gm-diesel-engines/21-6-5l-diesel-engine/915177-4l80e-repair-questions.html
 

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Discussion Starter #15
That makes a lot of sense. When I got my 93 and I put in the trans from a 94 I also replaced all the solenoids and the force motor in the trans. I probably ordered all parts for a 93. That would explain why it worked so well on the 93 TCU.
 

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You really want to watch what parts you install in a given 4l80e, as there are a variety of parts in them that have changed over time, and mixing and matching bits can have bad results.
 

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Discussion Starter #17
I got the truck back together a month ago. The trans shifts great and gives me no codes. That is until I hit 4th gear. If I keep it in 3rd and don't let it go to OD, it works fine as a 3 speed and even has lock up in 3rd. If I have it in OD and let it get up to speed, as soon as it it hits 4th, the computer commands 3rd and it down shifts. At this time it has no lockup. Restarting the truck clears the issue. The only code it gives is 68 when it tries OD. I have had it checked with a scan tool while driving and everything looks good. The computer just calls for 3rd after it reads a mismatched ratio in OD.

My plan is to have the trans that went bad completely rebuilt in a few months. Until then I have a 3 speed. As far as taking my chances on a $240 trans, I think I did alright. I just wish I had OD.
 

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Discussion Starter #18
I got my bad trans rebuilt. I was told that I destroyed everything between the front pump and the output planetary gears. Everything was replaced including the drum and the internals upgraded to a 97+ model. He also put in 4 clutches everywhere it had 3. I installed it with a new torque converter. All is good now. It shifts smooth and locks up immediately no matter how hard I drive it. I could not be happier with the build and it only cost me $1000.
 
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