As the speed of the vehicle continues to increase, the Powertrain Control Module (PCM) monitors the input signals from various engine and transmission sensors. The PCM uses this data to energize the 1-2 shift solenoid (SS) valve in order to shift the transmission into fourth gear at the appropriate time.

1-2 Shift Solenoid (SS) Valve

The PCM energizes (turns ON) the 1-2 SS valve. The PCM blocks the exhaust of 1-2 SS valve fluid to create high fluid pressure within the valve. High pressure at the 2-3 shift solenoid (SS) valve, at the end of the 1-2 shift valve, holds the valve in the upshifted position, while fluid from the 1-2 SS valve is routed to the end of the 3-4 shift valve.

3-4 Shift Valve

High fluid pressure in the 1-2 SS valve moves the 3-4 shift valve to the upshifted position. The 3-4 shift valve allows orificed third clutch fluid to enter the fourth band feed passage. Fourth band feed is then routed to the 1-2 shift valve.

1-2 Shift Valve

High fluid pressure in 2-3 shift solenoid (SS) valve holds the 1-2 shift valve in the upshifted position. The 1-2 shift valve allows fourth band feed fluid to enter the fourth band circuit. Fourth band fluid is then routed to the 3-4 accumulator piston and to the fourth servo piston.

3-4 Accumulator Piston

Fourth band fluid actuates the 3-4 accumulator piston. The piston cushions the apply of the fourth band assembly during a 3-4 shift. The 3-4 accumulator fluid on the spring side of the 3-4 accumulator piston is forced back through its circuit to checkball #3.

#3 Checkball (Primary Accumulator, 3-4 Accumulator)

The #3 checkball is located in the accumulator housing. The 3-4 accumulator fluid pressure unseats the checkball. The 3-4 accumulator fluid then enters the primary accumulator circuit and is routed to the 1-2 & 3-4 accumulator valve.

1-2 & 3-4 Accumulator Valve

The 1-2 & 3-4 accumulator valve is biased by torque signal pressure, third clutch pressure, and by orificed primary accumulator fluid pressure. The valve regulates the exhaust rate of primary accumulator fluid during a 3-4 shift.