4L80E & TH400 Tech.

[clinebarger]

Pressure Regulator & Boost Valve basics, From a Sonnax Tech article.


Raising line pressure is typically done by using a stronger pressure regulator spring, installing a larger boost valve or doing both.

A stronger spring and larger boost valve will both increase pressure, just not in the same way, so it's important to understand the differences before making any changes.

Stronger springs have a "linear" effect on pressure. This means you get the same amount of pressure increase at the low and high ends of the pressure range.

While a stronger pressure regulator spring will raise line pressure, there is a limit to how much you can get away with before troubles surface. A significant pressure increase that tightens upshifts under heavy load can be too much of an increase when shifting into reverse in the garage. This increase also puts extra load on the pump at idle and can result in the TCC clutch dragging due to reduced cooler flow.

Larger boost valves have a "progressive" effect on pressure: they change the rate of pressure increase. Using larger boost valves, it's possible to have a very small pressure increase at the low end of the pressure range and a far greater increase at the high end. This creates an ideal situation: smooth engagements and lower load on the pump at idle, plus a greater increase in pressure as the transmission is worked harder. The significance of changing the rate of pressure increase with larger valves – rather than simply increasing pressure by the same amount with springs – is that higher pressure is created when it is needed most.

[engairuph]

I'm still having a issue

[clinebarger]

Blocking the 3rd gear Accumulator on a 4L80E, Unbolt the 3rd/4th Accumulator housing from the Valve Body. (The Valve body has to be removed)

Remove both Accumulator Pistons, The one without a guide pin is the 3rd gear Accumulator, The Hole near the bottom of the big bore is what needs to be blocked. (arrow).




Using a 5/16-18 tap, Carefully tap the hole deep enough so the Set screw sits below flush, The Hole is at an angle....Try to keep the tap at that angle.




Test fit the set screw so you know it's seating below flush, You can make fun of the Gold Plated set screw if you want, I bought 2 boxes full of them from an Audio install shop that was going out of business.



You can Block the 4th Accumulator if you like (I generally don't unless a high stall converter is being used), It's the exact same method, Just remove the guide pin to tap the hole.

[clinebarger]

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.