To obtain Fourth gear, the PCM receives input signals from the VS Sensor and the TP Sensor in order to energize (turn ON) the supply of current to the 1-2, 3-4 shift solenoid valve (315). When energized, line pressure is directed into the 1-2, 3-4 shift solenoid valve passage and on to the 3-4 shift valve (362). Fluid from the 1-2, 3-4 shift solenoid valve moves the valve against spring pressure. This allows third fluid to enter both the fourth fluid passage and the fourth clutch fluid passage. Fourth fluid seats the #10 checkball (372). The fluid also forces the checkball through a feed orifice in order to stroke the 3-4 accumulator piston (428) while applying the fourth clutch. The 3-4 accumulator fluid on the spring side of the piston is forced through the 3-4 accumulator pin (426) into the 3-4 accumulator passage, and the fluid exhausts at the 3-4 accumulator valve (350).

The 1-2, 3-4 shift solenoid valve energizes in order to prevent fluid from exhausting out of both the line passage and the 1-2, 3-4 shift solenoid valve passage.

Spring pressure combines with off fluid pressure from the end of the 2-3 shift solenoid valve in order to hold the 1-2 shift valve against the 1-2, 3-4 shift solenoid valve.

When shifted against a spring force, the 3-4 shift valve allows third fluid to enter both the fourth fluid passage and the fourth clutch fluid passage. Fourth fluid seats the #10 checkball (372). The fluid is then forced through a feed orifice before stroking the 3-4 accumulator piston (428) and applying the fourth clutch.

The #10 checkball is located in the valve body (300). The checkball forces fourth fluid through a feed orifice into the fourth clutch passage in order to stroke the 3-4 accumulator piston (428).

The 3-4 accumulator piston cushions the application of the fourth clutch by using fourth clutch fluid to stroke the piston against a spring force and also against the 3-4 accumulator fluid.

The 3-4 accumulator valve controls the rate of exhaust of the 3-4 accumulator fluid during fourth clutch application.