SHAFT-PINION 6W4764 - Caterpillar

Shifting to First Speed Forward with a Running Engine
Illustration 3 g03379181
Schematic for the transmission hydraulic system (neutral, engine running)
(1) Solenoid valve (for the Number 2 clutch)
(2) Solenoid valve (for the Number 3 clutch)
(5) Solenoid valve (for the Number 6 clutch)
(11) Flow control orifice
(12) Torque converter
(15) Torque converter ratio valve
(17) Modulating relief valve
(18) Second speed and fourth speed selector spool
(20) Port for Number 3 clutch
(21) Direction selector spool
(22) Port for Number 5 clutch
(23) Port for Number 2 clutch
(24) Port for Number 1 clutch
(26) Pressure differential valve
(27) Transmission charging pump
(28) Port for Number 6 clutch
(30) Load piston
(34) Port for Number 4 clutch
(35) First speed and third speed selector spool
(AA) P1 Speed clutch oil
(BB) P2 Direction clutch oil
(CC) P3 Torque converter inlet oil
(DD) Torque converter outlet oil
(EE) Lubrication oil
(FF) Return oil
(GG) Pilot oil When the transmission direction control is moved to the FORWARD position, and the transmission speed control is shifted to the FIRST SPEED position, the electronic transmission control activates solenoid valve (1) and solenoid valve (5). Solenoid valve (2) is deactivated.Solenoid valve (1) directs oil to the top end of direction selector spool (21). Spool (21) moves downward. Pump oil flows around the spool to Number 2 clutch.Solenoid valve (5) directs oil to the left end of first speed and third speed selector spool (35). Spool (35) moves to the right and pump oil flows around the spool. The pump oil then flows to Number 6 clutch.Solenoid valve (1) directs oil from the top end of second speed and fourth speed selector spool (18) to the reservoir. Spool (18) moves upward and pump oil is closed to Number three clutch.When the shift to first speed forward is made, Number 3 clutch is opened to the reservoir. The pressure in the system decreases. Springs move modulating relief valve (17) upward. Springs also move pressure differential valve (26) upward until the large orifice at the top end of pressure differential valve (26) is closed to pump oil by the valve body.As pressure differential valve (26) moves upward, the chamber behind load piston (30) opens to the reservoir. This allows the springs to move the load piston downward.The speed clutch oil starts to fill Number 6 clutch.When Number 6 clutch is full of oil, the pressure in the speed clutch circuit starts to increase. This pressure increase is felt in the slug chamber of modulating relief valve (17) and in the chamber at the top of pressure differential valve (26).The oil that flows to pressure differential valve (26) starts to fill the chamber at the top of the valve spool. The chamber is filled through the small orifice.When the pressure in the Number six clutch is approximately 380 kPa (55 psi), pressure differential valve (26) starts to move downward. The movement of the valve spool opens Number 2 clutch to pump oil. The movement of the valve spool also closes a passage from the chamber behind load piston (30) to the reservoir.When the Number 2 clutch is full of oil, the pressure increases