4l60e Overdrive
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Teching In
Joined: Mar 2013
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4l60e Overdrive everything in the transmission works fine. after shifting to od and going up a slight incline the transmission wants to downshift to third but it doesnt. it will try to downshift and the rpm gauge will surge like it tries to but it doesnt engage into 3rd but it dont actually go in and goes right back to od. if you press the gas harder it will downshift to like it is suppose to but if you are in od and just cruising and like i said go up a small small small incline it will surge back and forth from 3rd to od but wont fully engage into third. any ideas as to what this could be? 2001 gmc Z71 transmission was built a year ago with the best stuff you can put in it
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Joined: Aug 2010
Posts: 7,323
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From: Ann Arbor, MI
I'm not an expert and kinda guessing here, but this sounds like the shift points in the tune are too close, combined with a sticking servo or leaking 3-4 accumulator.
The servo is often pretty easy to remove in trucks (unlike tight F-body).
If 1st, 2nd and 3rd are good, your trans internals are in good shape. 4th gear is a combination of 2nd and 3rd.
The servo is often pretty easy to remove in trucks (unlike tight F-body).
If 1st, 2nd and 3rd are good, your trans internals are in good shape. 4th gear is a combination of 2nd and 3rd.
Moderator
Joined: Aug 2010
Posts: 7,323
Likes: 529
From: Ann Arbor, MI
A servo is generally easy to repair. You can get a seal kit for $15.
I have pictures showing how to remove the servo in the thread:
https://ls1tech.com/forums/automatic...ry-smooth.html (Post #8)
This thread is close to your problem:
https://ls1tech.com/forums/automatic...-into-4th.html
I have pictures showing how to remove the servo in the thread:
https://ls1tech.com/forums/automatic...ry-smooth.html (Post #8)
This thread is close to your problem:
https://ls1tech.com/forums/automatic...-into-4th.html
Moderator
Joined: Aug 2010
Posts: 7,323
Likes: 529
From: Ann Arbor, MI
The 1-2 accumulator is trivial to check/fix.
However the 3-4 accumulator is under the separator plate. You have to remove the 1-2 accumulator AND the entire valve body to get to it. Since your trans was rebuilt a year ago, hopefully the separator plate is still in good shape; I'd replace the gaskets but that is trivial and cheap.
Replacing the valve body (VB) requires getting the 7 check ***** in place and one in the case. (Hold them in place with vaseline.) Also critical to get the various length VB bolts in the right location.
The Transgo HD2 kit instructions posted here are useful for that:
https://ls1tech.com/forums/automatic...questions.html
There were 4 or 5 threads in the past year about 4th gear problems. IIRC, one was a servo problem, one had the 4th piston in the servo backwards, one had a problem in the 3-4 accumulator and one needed to have the valve body replaced.
If the other gears work perfectly, it is unlikely the trans needs to be removed to fix a 4th-gear-only problem.
However the 3-4 accumulator is under the separator plate. You have to remove the 1-2 accumulator AND the entire valve body to get to it. Since your trans was rebuilt a year ago, hopefully the separator plate is still in good shape; I'd replace the gaskets but that is trivial and cheap.
Replacing the valve body (VB) requires getting the 7 check ***** in place and one in the case. (Hold them in place with vaseline.) Also critical to get the various length VB bolts in the right location.
The Transgo HD2 kit instructions posted here are useful for that:
https://ls1tech.com/forums/automatic...questions.html
There were 4 or 5 threads in the past year about 4th gear problems. IIRC, one was a servo problem, one had the 4th piston in the servo backwards, one had a problem in the 3-4 accumulator and one needed to have the valve body replaced.
If the other gears work perfectly, it is unlikely the trans needs to be removed to fix a 4th-gear-only problem.
