Low signal pressure to shift solenoids A and B.
Recalibrated springs for 1-2 and 2-3 shift valves.
In 4th gear, signal A oil force must overpower the 1-2 shift valve spring and opposing signal B pressure in 4L80-E transmissions. If the 1-2 shift valve does not remain fully stroked, drive oil to second and direct will be cut off or go to exhaust. The reaction area of A is greater than that of B, so the spring is the stroking factor. Complaints of second gear starts, neutral after 2-3 shift or no 4th gear are compounded by worn AFL limit bores, leaking O-rings and solenoids. When AFL oil drops, and signal A becomes less than 58 psi, the 1-2 valve will stall or float. This 3-1 or complaint of 3rd neutral will occur in OD or D with scanner indication of 4th commanded. This spring kit 34994-02K replaces the original 1-2 shift valve spring and 2-3 shift valve spring.