Hydraulic System Operation The hydraulic system shown in figure 7-19 has the following five basic functions.

1. The planetary holding devices are all actuated by hydraulic pressure from hydraulic slave systems (fig. 7-20).

2. It keeps the torque converter charged with fluid at all times.

3. The shifting pattern is controlled by the hydraulic system by switching hydraulic line pressure to programmed shifting devices according to vehicle speed and load.

4. It circulates the oil through a remote oil cooler to remove excess heat that is generated in the transmission and torque converter.

Figure 7-20. - Lockup band actuated by hydraulic pressure.

5. The hydraulic system provides a constant supply of lubricating oil to all critical wearing surfaces of the transmission.

Figure 7-19. - Typical hydraulic schematic of a three-speed automatic transmission.