P O W E R T R A I NT R A N S M I S S I O N H Y D R A U L I C C O N T R O LSTM 5-3805-258-24-1S Y S T E M S O P E R A T I O NEngine Running(Neutral to First Speed Forward)TRANSMISSION HYDRAULIC CONTROLS(First Speed Forward)6.No. 5 clutch.13. Modulation relief valve.7. No. 4 clutch.14. Pressure differential6.No. 6 clutch.valve.10. Speed selection spool.16. Ratio valve for torque11. Load piston.convertar.12. Transmission neutralizer17. Direction selection spool.valve.16.No. 1 clutch.When the transmission selection lever is moved toFIRST SPEED FORWARD, speed selection spool(10) and direction selection spool (17) are in thepositions shown in the schematic.The position of direction selection spool (17) opensa passage to No. 2 clutch (20). It also opens passagesfrom No. 3 clutch (19) and No. 1 clutch (18) to thereservoir.The position of speed selection spool (10) opens apassage from No. 6 clutch (8) to pump oil. It alsoopens No. 4 clutch (7) and No. 5 clutch (6) to thereservoir.19.No. 3 clutch.E. Pressure tap for speed20.No. 2 clutch.clutch (Pi).22. Flow control orifice.F. Pressure tap for directionD. Pressure tap for converterclutch (P2).inlet.When the shift to FIRST SPEED FORWARD ismade, the No. 3 clutch is opened to the reservoir. Thepressure in the system decreases. Springs move mo-dulation relief valve (13) toward the left. Springsmove pressure differential valve (14) toward the leftuntil the large orifice at the left end of valve (14) isclosed to pump oil by the valve body.As the pressure differential valve moves towardthe left, the chamber behind load piston (11) opens tothe reservoir. This lets the springs move the loadpiston to the right. The pressure differential valve isin a position to let the pressure increase in the speedclutch circuit.The speed clutch oil starts to fill No. 6 clutch (8).3-45
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