SCREW 2F8337 - Caterpillar

Illustration 1 g03313957
View of the top of the transmission
(1) Number 1 clutch modulating valve
(2) Number 2 clutch modulating valve
(3) Number 3 clutch modulating valve
(4) Number 4 clutch modulating valve
(5) Number 5 clutch modulating valve
(6) Number 6 clutch modulating valve
(7) Number 7 clutch modulating valve
(8) Main relief valve
(9) Lubrication relief valve (transmission)
(10) Modulating valve (torque converter lockup clutch) The transmission hydraulic control directs the oil to the torque converter, the transmission clutches, and the lubrication circuits. The transmission hydraulic control also controls the flow of oil to the clutches. The transmission hydraulic control is installed on the top of the transmission planetary group. The transmission hydraulic control consists of the following components: main relief valve (8), clutch modulating valves (1) through (7), lubrication relief valve (9), and torque converter lockup clutch modulating valve (10).Pressurized oil for the operation of the transmission hydraulic control flows from the power train gear pump to the transmission oil filter. The oil flows from the power train oil filter to the transmission inlet on the right side of the transmission. The oil flows through internal passages in the transmission housing in order to supply the components in the transmission hydraulic control with oil.The seven modulating valves are mounted on the top of the transmission. The seven transmission clutches have an individual modulating valve. In order to move the machine, two clutch solenoids must be energized. The modulating valves are used to directly modulate the oil pressure that is sent to each individual clutch.Table 1 provides the combination of the energized solenoids and engaged clutches for each forward speed and for reverse.
Table 1
Assignments for the Transmission Clutch
Gear Clutches
1 2 3 4 5 6 7
Reverse X X
Stall X X X
Neutral X
First X X
Second X X
Third X X
Fourth X X
Fifth X X
Sixth X X
Seventh X X Main Relief Valve
Illustration 2 g03316689
(A) Passage from gear pump
(B) Passage to reservoir
(1) Spring
(2) Ball
(3) Orifice
(4) Spool
(5) Spring
(6) Piston
(7) Adjustment screw The main relief valve regulates the pressure of the oil that is supplied to modulating valves. Oil from passage (A) comes into the main relief valve, through orifice (3), and against ball (2). When oil pressure exceeds maximum required pressure of the system, the oil pushes ball (2) against spring (1). The oil pressure unseats ball (2) and begins to move spool (4) against spring (5). With enough pressure, spool (4) will travel far enough to allow oil to flow into passage (B) and back to the reservoir. Adjustments to the main relief valve can be made at adjustment screw (7). Adjustment screw (7) moves piston (6). The position of piston (6) determines the length of spring (5) and the amount of force required to relief the oil pressure.