PISTON 1489039 - Caterpillar

Illustration 1 g00661316
Transmission Hydraulic Control
Illustration 2 g01463049
Selector and Pressure Control Valve
(1) Modulation relief valve
(2) First speed and third speed selection spool
(3) Second speed selection spool
(4) Selector valve body
(5) Torque converter inlet ratio valve
(6) Direction selection spool
(7) Selector and pressure control valve body
(8) Pressure differential valve
(9) Load piston The following items are inside the top cover of the transmission: selector and pressure control valve body (7) and selector valve body (4). Selector spools (2), (3), and (6) are moved when oil pressure is applied to one end of the spool. Each solenoid controls the oil pressure to the end of one spool. If no pressure is going to the end of a spool, then that end is opened to the drain. The power train ECM activates the solenoids in order to control the speed of the transmission and the direction of the transmission.
Table 1
Valve Function
(1) Modulation relief valve. This valve controls the maximum pressure in the system.
(2) First speed and third speed selection spool. This valve directs oil to the first speed clutch or to the third speed clutch.
(3) Second speed selection spool. This valve directs oil to the second speed clutch.
(5) Torque converter inlet ratio valve. This valve limits the maximum pressure to the torque converter.
(6) Direction selection spool. This valve directs oil to a direction clutch.
(8) Pressure differential valve. This valve keeps a pressure differential between the speed clutches and the direction clutches.
(9) Load piston. This valve controls the rate of pressure increase in the clutches.