3-4 Shift Valve

During 3rd gear, the shift solenoid valve # 2 is turned ON. Line pressure to one of the passages of the 3-4 shift valve is exhausted. Spring force moves (closes) the valve, shutting off line pressure to the overdrive brake (releasing it), and directing line pressure to the overdrive clutch (applying it).

During 4th gear, the shift solenoid valve # 2 is turned OFF. Line pressure is directed to one of the passages of the 3-4 shift valve. The valve moves
(closes) and shut-off line pressure to the overdrive clutch (releasing it), and directs line pressure to the overdrive brake (applying it).

During 1st gear operation, the shift solenoid valve # 2 is turned OFF. This applies line pressure to two passages of the 3-4 shift valve. Therefore, having line pressure at both sides of the 3-4 shift valve cancels out any valve movement.