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I just put a basic overhaul kit in my friend’s 4l60e because she thought it needed to be rebuilt. She attempted to pull the transmission herself first and the truck sat for over a year when she got stuck because of the y-pipe nuts stripping. Then she finally had it towed to me and I put an overhaul kit in at her request. I go to test drive and it has a flare during the 2-3 shift. I ask her if it was doing this before and she said yes that’s why she wanted to rebuild it. What am I missing that could cause this?
I have the same problem with a 4l65E and found a couple interesting things to try before you drop it out again. Ya, theres lots of internal things that can cause that but these are cheap and easy enough to try first.
1)There is a GM jumper wire available (any wire will do) that adds a redundant ground to the trans computer because apparently the PC board cracks.
2) The other thing I found was to replace that solenoid in the valve body. It can still be working, but is lazy and causes that flare.
Both things I found searching Google and ended up on Youtube.
For what its worth, I dealt with a 2-3 flare/ slide-bump with a friends stock '03 Silverado after a rebuild. I tried tuning the shifts in HPT and it seemed to help, but still would be intermittent, especially from 1/2-3/4 throttle. Anything under/ over that amount and it would shift fine. I finally decided to chuck a Corvette servo at it in addition to reseting the trans tuning back to stock, and it cured it. It makes sense since the servo functions as the 3rd apply accumulator as well.
2-3 Flare can be caused by a number of things, Excessive large 3rd accum feed hole, missing checkball, excessive 3-4 clearance, inadequate pressure rise at higher throttle PCS aka EPC solenoid issue, Leaking encapsulate check ball in case debris can get stuck, Leaking check valve in the input drum. Grooves in stator are among the most common. As someone mentioned also a ground issue with the PCM https://www.sonnax.com/tech_resource...a-bad-computer. Though I would tend to look hydraulic issues first myself.
Frank
Thanks for all the suggestions so far. To be honest, this is the first transmission I’ve torn apart. The truck drove fine for a bit, and then started having the slip going into third. She said that is why she originally started taking it apart also, it slipping going into third.
I am putting a corvette servo in it tomorrow to see if that could be an issue (couple of the seals and one piston did feel loose).
I saw people talking about the ground for the computer but after research, I thought that issue had been fixed long before her truck came out (2009).
I also will reset the transmission adaptive with my scantool when I get it back together.
might not be a bad idea to check the servo pin travel. you can check it before you put the seals on the new servo. usually measure with a dial indicator if you have room.
might not be a bad idea to check the servo pin travel. you can check it before you put the seals on the new servo. usually measure with a dial indicator if you have room.
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4L60E 2-3 shift flare 
