Now onto the hydraulic. Repeated DTCs 86, 87 and no 4th gear

SONNAX Sells the recalibrated spring kits for the 1-2 and the 2-3 shifting valves. The weak springs can cause low signal pressure to the shifting solenoids.
Whether you choose to replace them is of your own accord. I am informing the forum.

Remember that the 4th gear is supplied through the 2nd gear shifting valve. Both 1-2 and the 2-3 valves need to be actuated by the shifting solenoids. They can do their job all day long but if the pressure isn't there then the valves will not actuate enough.
The shifting valves supply signal pressure.

At the back of the shifting valve there is a return spring. This spring can get weak.

AFL VALVE:

The Actuator feed limit valve is considered the work horse of the GM transmission. The 4L80-E is no exception. This valve is the valve that supplies pressure too the shifting valves. The problem with the Actuator Feed limit Valve is this.

Side loading. Wearing out the aluminum bore in the valve body.
The pressure control solenoid (PCS) or Electronic pressure control solenoid (EPC) sends the pressure signal to this valve.
This solenoid is a variable width solenoid and works by adjusting the amperage. It is 12 volt DC constant. If the amperage is lowered then the line pressure is ultimately increased.

The actuator feed limit valve reroutes hydraulic signal pressure to the shifting valves. The 1-2, the 2-3 and ultimately to 4th.

To help you understand why this valve wears.
Moving steel against aluminum will wear out aluminum. The valve bore.
The reaction area within the AFL valve as it is called is large. The oil pressure coming from the pressure control solenoid AKA (EPC) continously ramps up or down. Over time this causes wear.
The location of the AFL valve is to the left of the shifting solenoids.
To the left of the AFL valve is an internal filter. The filter cavity should be WAT Tested. Wet Air Tested. The filter has an O-ring that can leak.
Transmission shops need to resleeve this bore.

Torque converter front stator support bushing.


The stator is a force multiplier. It helps the turbine move quicker by pushing fluid so to speak to the turbine.

When the stator is not needed it freewheels. This is done when the turbine speed catches up to the pump speed or engine speed (same thing)
When the turbine is trying to catch up to the pump speed the stator assists by reinforcing fluid back to the turbine.
This is what gives your transmission the hydraulic boost you need. It helps maximize torque. It gives the turbine steroids.
The turbine is what powers the transmission. It receives it's torque from the Torque converter pump.

The turbine shaft is what transports the torque into the transmission.

If you remove the torque converter you will see a fixed splined shaft that does not move. These splines support the stator.The inner diameter of this barrel so to speak has the stator support bushing. The support bushing encircles the turbine shaft that goes back into the transmission.

The turbine shaft is also supported from this bushing.

When this suport bushing wears wear out you can receive various DTC codes. Among those codes are DTC 68 Transmission component slipping.

A worn bushing can be a cause of leakage.

Other problems associated with a worn stator support bushing.
DTC 85, DTC 86 and DTC 87 Ratio error codes.

Torque converter bushing is located here.


http://i120.photobucket.com/albums/o187/USMILRET/4L80E%20Transmission/th_Bushing.jpg (http://i120.photobucket.com/albums/o187/USMILRET/4L80E%20Transmission/Bushing.jpg)