WASHER 1204871 - Caterpillar

Engine Running (Neutral To Forward)
Transmission Hydraulic Control Valve
(4) Transmission control valve. (5) Neutralizer solenoid. (6) Neutralizer valve. (7) Flow control spool. (8) Forward/reverse selector valve. (10) Load piston. (12) Relief valve. (13) Check valve for load piston. (14) Orifice for load piston. (A) Pressure tap for reverse clutch. (C) Pressure tap for forward clutch. (D) Pressure tap for torque converter inlet. (G) Pump oil. (H) Return oil. (J) Converter inlet oil.When the direction control lever on the steering wheel column is moved to the forward position (away from the driver), the linkage moves forward/reverse selector valve (8) to the forward position.With the engine running, oil pump (11) pulls oil from reservoir (18), through screen (16), to the pump. The pump sends the oil through filter (9) to the control valve.Oil pressure moves flow control spool (7) to the right. This allows oil not needed by the transmission circuit to flow to the torque converter circuit.Oil needed by the transmission circuit flows through the orifice in the center of the flow control spool and goes to forward/reverse selector (8). With the selector valve in the forward position, oil is directed to the forward clutch assembly. The reverse clutch oil passage is open to drain. Oil fills the forward clutch and then modulation occurs.Orifice (21) maintains oil pressure to 4-WD clutches when oil pressure drops during transmission directional clutch shifts.The function of modulating relief valve (12) and load piston (10) is to control the rate of the pressure increase in the directional clutch circuit and limit the final clutch pressure as follows for smooth engagement of the clutch.As the pressure in the transmission circuit increases, relief valve (12) starts to move to the right and load piston (10) starts to move to the left. Orifice (14), in the supply passage to the load piston, causes the oil to go to the area behind the load piston at a specific rate. As the relief valve moves to the right and the load piston to the left, the pressure in the forward clutch assembly increases gradually. This gradual increase in pressure is known as modulation.When the load piston reaches its full stroke the relief valve will relieve excess flow to the reservoir and maximum system pressure is reached.Since neutralizer solenoid (6) has not been activated nothing occurs to change the clutch engagement.Engine Running (Forward To Reverse)
When the direction control lever on the steering wheel column is moved from the forward position to the reverse position, the linkage moves forward/reverse selector valve (8) from the forward to the reverse position.Orifice (21) maintains oil pressure to 4-WD clutches when oil pressure drops during transmission directional clutch shifts.As the selector valve changes position it passes through the neutral setting. At this position the system pressure is open to reservoir, causing modulating relief valve (12) and load piston (10) to return to a neutral position. The spring behind the load piston forces the oil to drain by opening check valve (13). As oil drains, load piston