Hi all, I just finished rebuilding my 4L70e (basically same as 4l60e) in my 2008 Avalanche. I did a basic Alto rebuild kit along with installing a corvette servo. The trans worked great and shifted firm into every gear for about a week. I went to take off and it shifted good from first to second, then just went into what felt like neutral instead of third. I instantly let off the gas and pulled over to check the fluid, it was still full and not burnt. It never slipped, just released the second gear band and won’t activate the 3rd gear clutches causing it to go back into first. The truck hasn’t thrown any codes, and the solenoids are not the issue because the 2nd gear band releases. I am stumped because it worked great for over 50 babied miles. Anyone had this issue or have any ideas? Also is there a way to air check the 3rd gear clutch pack through the case or valve body?
Thank you, BadK5

 

It sounds like there's a chance you may have nicked one of the teflon rings for the input drum, and it's barely making itself known.

 

Yes that is a possibility, know if I can air test the circuit while still in the truck?

 

Yes...
With the Valve-Body and Separator-Plate removed.

Look at the Image below...
Find the case Worm-Track / Hole that matches-up to the Pump Passage for the 3-4 Clutch:

 

Do you know what one it is on the case?

 

Yes, of course I do...
However my confidence in you doing this properly is not very high.
I do wish you luck though.


Below is a Case Passage Diagram that I modified for you.
Fluid/ Passage #29 (circled in Blue) is what you want.
At the top of the Passage (near the Pump) is the Hole that you want.

 

Thank you, this is exactly what I was looking for!