Overdrive Range - Fourth Gear

Overdrive Range - Fourth Gear:

OVERDRIVE RANGE - FOURTH GEAR

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

4TH BAND APPLIES

Shift Solenoid "A": Energized (ON) by the PCM, it blocks the exhaust of solenoid "A" fluid to create high solenoid "A" fluid pressure. High solenoid pressure "B" at the end of the 1-2 shift valve holds the valve in the upshifted position while solenoid "A" fluid is routed to the end of the 3-4 shift valve.

3-4 Shift Valve: Moved to the upshifted position by high solenoid "A" fluid pressure, it allows orificed 3rd clutch fluid to enter the 4th band feed passage. 4th band feed is then routed to the 1-2 shift valve.

1-2 Shift Valve: Held in the upshifted position by high solenoid "B" fluid pressure, it allows 4th band feed fluid to enter the 4th band circuit. 4th band fluid is then routed to the 3-4 accumulator piston and the 4th servo piston.

3-4 SHIFT ACCUMULATION

3-4 Accumulator Piston: Actuated by 4th band fluid, it cushions the apply of the 4th band assembly during a 3-4 shift. 3-4 accumulator fluid on the spring side of the 3-4 accumulator piston is forced back through its circuit to check-ball #3.

#3 Checkball (Primary Accum 3-4 Accum): Located in the accumulator housing, it is unseated by 3-4 accumulator fluid pressure. 3-4 accumulator then enters the primary accumulator circuit and is routed to the 1-2 & 3-4 accumulator valve.

1-2 & 3-4 Accumulator Valve: Biased by torque signal pressure, 3rd clutch pressure and orificed primary accumulator fluid pressure, it regulates the exhaust rate of primary accumulator fluid during a 3-4 shift.