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4L80E slipping in first then not shifting

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brodie

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I just replaced my flex plate and starter on my 6.5 detroit with a 4l80e. It was running and driving great until 3 days ago when I was going up a pretty steep hill and then it leveled out and wouldn’t shift out of 1st gear. I pulled over and put the truck in park and shut it off then turned it on again and it was driving perfectly fine. Then yesterday it started slipping pretty badly in first gear and it’s still doing it today but only with the load from a dead stop start. For extra information it’s currently leaking out of the tail shaft seal and is overfilled on tranny fluid. Also there’s a loud buzzing noise coming from the transmission/transfer case but when I push up on it it goes away. That noise only happens here and there not very often.

Could I have messed something up when pulling the transmission?
 
brodie said:
I just replaced my flex plate and starter on my 6.5 detroit with a 4l80e. It was running and driving great until 3 days ago when I was going up a pretty steep hill and then it leveled out and wouldn’t shift out of 1st gear. I pulled over and put the truck in park and shut it off then turned it on again and it was driving perfectly fine. Then yesterday it started slipping pretty badly in first gear and it’s still doing it today but only with the load from a dead stop start. For extra information it’s currently leaking out of the tail shaft seal and is overfilled on tranny fluid. Also there’s a loud buzzing noise coming from the transmission/transfer case but when I push up on it it goes away. That noise only happens here and there not very often.

Could I have messed something up when pulling the transmission?
Click to expand...
Also the truck currently doesn’t have boost because of a bad leak on the crossover pipe to the turbo so that may have something to do with it I believe
 
If you have a cooling loop that is in your unknown xfer case- it can be failed leaking into the case.

You can have bad mount since pushing up on it eases a sound that shouldn’t be there. This could warp the trans case, or flex the worm tracks. If the case is married instead of a divorce mount.
Also the gear shift to either could be getting pulled out of position.

Drain the fluid to the correct level and start from there. Verify fluid level in xfer case, examine for shavings. Even if you have to drain it then put same fluid back in- just starting with a clean container.
 
Will L. said:
If you have a cooling loop that is in your unknown xfer case- it can be failed leaking into the case.

You can have bad mount since pushing up on it eases a sound that shouldn’t be there. This could warp the trans case, or flex the worm tracks. If the case is married instead of a divorce mount.
Also the gear shift to either could be getting pulled out of position.

Drain the fluid to the correct level and start from there. Verify fluid level in xfer case, examine for shavings. Even if you have to drain it then put same fluid back in- just starting with a clean container.
Click to expand...
Is there any way to drain the tranny fluid other than dropping the pan on these trannys?
 
Will L. said:
there is a kit to add a drain plug so the first time you do a drop& splash becomes the last.
B&M makes an ok one but the drain hole is small. I can’t remember who makes the bigger one off hand
Click to expand...
Gonna try to drain some out right now I’ll let you know if it fixes anything
 
Will L. said:
Draining the excess won’t help unless the breather is filled up.
But step one is look for problems, step two is fix known problems before moving onto step three
Click to expand...
Welp I just got it to the correct level and no difference. Still fine when cold then starts slipping once I drive around for about 3-5 minutes. All other gears are fine and it’s effecting reverse now.
 
Will L. said:
Draining the excess won’t help unless the breather is filled up.
But step one is look for problems, step two is fix known problems before moving onto step three
Click to expand...
Just checked for codes and it’s throwing code 68 which from what I’m seeing could be anything from input/output shaft speed sensors to needing a transmission revuild
 
Haha, you just jumped to the next level with that connection.
Now that it won’t overflow and soak the outside of that connection, clean it with electrical cleaner inside & out. Drive and see if atf leaks through the connection.
If so that short harness needs replaced. But there is a 90%+ possibility you are needing a full rebuild/replacement. So how much money you pour into trying to save this trans is something you need to determine ahead of time.

A warning- something many many people do is find another used 4l80e and assume they all interchange. They don’t. From here is time to start finding defective parts and replacing them with crossed fingers, knowing all the money is a waste most likely slipping 1st & reverse.
 
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