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| Illustration 1 | g00874564 |
Transmission Hydraulic Control Group (1) Six clutch solenoid modulating valves (2) Transmission hydraulic control relief valve (3) Torque converter inlet relief valve (4) Oil inlet from the pump (5) Oil outlet to the torque converter | |
The transmission hydraulic control group controls the oil pressure to the torque converter and to the transmission clutches. The transmission hydraulic control group is installed on the top of the transmission planetary group. The transmission hydraulic control group consists of the following components: six clutch solenoid modulating valves (1), transmission hydraulic control relief valve (2) and torque converter inlet relief valve (3) .
Pressurized oil for the operation of the transmission hydraulic control group flows from the transmission oil pump to the transmission oil filter. The oil flows through a hose to the oil inlet in the torque converter housing. The oil flows through internal passages in the torque converter housing in order to supply transmission hydraulic control relief valve (2) with oil. The oil also flows to six clutch solenoid modulating valves (1) .
The six clutch solenoid modulating valves (1) are mounted on the top of the transmission under the top cover. Each transmission clutch has an individual clutch solenoid modulating valve (1). In order to move the machine, a direction clutch solenoid and a speed clutch solenoid must be energized. The clutch solenoid modulating valves (1) are used to directly modulate the oil pressure that is sent to each individual clutch.
The following table provides the combination of the energized solenoids and engaged clutches for each forward speed and for each reverse speed.
| Speed Range and Direction | Energized Solenoids and Engaged Clutches |
| Fourth Speed Forward | 3 and 2 |
| Third Speed Forward | 4 and 2 |
| Second Speed Forward | 5 and 2 |
| First Speed Forward | 6 and 2 |
| Neutral | 3 |
| First Speed Reverse | 6 and 1 |
| Second Speed Reverse | 5 and 1 |
| Third Speed Reverse | 4 and 1 |
| Fourth Speed Reverse | 3 and 1 |
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| Illustration 2 | g00563238 |
(2) Transmission Hydraulic Control Relief Valve (3) Torque converter inlet relief valve (6) Inlet chamber (7) Discharge chamber (8) Sump passage (9) Main relief valve (10) Transmission control passage | |
Transmission hydraulic control relief valve (2) controls the pressure of the oil that is supplied to clutch solenoid modulating valves (1) and the torque converter. The oil pressure must overcome the spring force of main relief valve (9). This will maintain a stable supply pressure to clutch solenoid modulating valves (1).
The supply oil pressure to transmission hydraulic control relief valve (2) is maintained by main relief valve (9) which is set at a minimum pressure of 2620 ± 35 kPa (380 ± 5 psi). Oil enters transmission hydraulic control relief valve (2) through inlet chamber (6). The oil flows past main relief valve (9) to transmission control passage (10) until the pressure setting of main relief valve (9) is exceeded. The main relief valve will move to the right. This will allow the excess oil to flow into passage (7) and to the torque converter. The maximum converter inlet pressure is controlled by torque converter inlet relief valve (3) which is set at 1060 ± 100 kPa (154 ± 15 psi). When the converter inlet pressure reaches the maximum, the torque converter inlet relief valve will open. The excess oil will flow through passage (8) and the oil will then return to the oil sump.
Reference: For additional information on the operation of the clutch solenoid modulating valves, refer to the Service Manual module for Systems Operation, "Power Train Electronic Control System" for the machine that is being serviced.