This is Important, Even to you guys that are throwing shift kits in a working 100,000 mile unit!
4L80E's have issues with the Actuator Feed Limit (AFL) Valve wearing the Valve Body.
The AFL valve regulates actuator feed pressure to all three shift valves, to the pressure control solenoid and to the 1-2 and 2-3 shift solenoids. The pressure is not fed to any clutches but is used to position the shift valves, which then will direct line pressure to the appropriate clutch.
When AFL Pressure starts to drop from wear....The Pressure drop over time is small at first, Then the wear/pressure loss starts accelerating to the point the valve is starting to take chunks out the Valve Body. (Not Linear)
This problem will first appear after you take a long hot 100+ mile trip & it Falls out of 4th, Then it starts falling out anytime the unit hot, Wrong Ratio codes, TCC codes, Shift Solenoid codes, Limp mode, & Random 2nd Gear starts........That all the new Solenoids, Harnesses, Tuning, & Half a$$ Rebuilds in the world will NOT fix.
There are 2 fixes for this.
The preferred method is to Ream the Bore larger, Install a Steel Sleeve & install a new AFL Valve. The Sonnax "Sure Cure" kit is a great product & does more than just the AFL Valve, The Tool Kit alone is over $300 (Reamers & Guides), That is not including the Sure Cure kit itself.
The 2nd choice is to Oversize the Bore & Install a Oversized AFL Valve, Transgo has a kit with the Reamer/Guide/Valve/Spring. Part# 48-ACT-TL (It actually fixes 6 Valve Bodies)
http://www.transgo.com/products.php?...dcountview=Yes
It is under $100 & worth every penny, The down side is.....The valve body will eventually wear again, But good for another 100K.
I'm going to cover the Second Choice, Because the cost & Ease of install.
Locate The AFL Vale Bore (Next to the TCC PWM Solenoid), Depending on year model, Remove the Roll pin & Plug(Early), Or The Clip(Late, Shown), Remove Spring & Valve.
Comparing the 2 Valves, You will only be enlarging the Smaller Spool, The Larger Land is just longer to ride on an "Unworn" part of the Valve Body.
Reamer & Guide
Guide & Reamer in place...
Follow the Directions, DO NOT ream past or into the "Wall" the Valve bottoms out on, The "Wall" is where all the cuttings are.
This was performed on a 150,000+ mile '01 Core, The Middle Land was worn the most, This is a before shot.
