In 4th Gear, signal A oil force must overpower the 1-2 shift valve spring and opposing signal B pressure in GM 4L80-E and 4L85-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 2nd 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. Sonnax 1-2 and 2-3 shift valve spring kit 34994-02K replaces the original 1-2 shift valve spring and 2-3 shift valve spring.
Springs MUST be used together. This is not a fix for leaking solenoids or leaking seals in the solenoid signal circuitor actuator feed limit circuit. See AFL limit valve repair 34200-16K.
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