Pressure In The Transmission Hydraulic Control System
A number of important components of the power train are supplied and controlled by oil from the transmission pump. The pressure in the system is regulated by the transmission hydraulic control relief valve. This valve serves the dual purpose of regulating the system pressure and supplying the correct pressure of oil to the torque converter.
Tests may be carried out in order to determine whether the transmission pump is supplying the correct amount of oil for each of the components in the system.
The following pressures can be tested in order to determine whether the oil that is supplied is sufficient.
- Transmission Oil Filter Inlet
- Transmission Hydraulic Control Relief Valve
- Torque Converter Lockup Clutch
- Planetary Transmission Clutches
- Relief Pressure For The Torque Converter Inlet
If insufficient oil pressure is measured anywhere in the transmission hydraulic control system, test the pressure of the oil at the oil filter inlet. Refer to Specifications, Systems Operation/Testing and Adjusting, "Hydraulic Oil Contamination - Test". If the pressure at the oil filter inlet is within specifications, test the pressure at the transmission hydraulic control relief valve. Refer to Specifications, Systems Operation/Testing and Adjusting, "Relief Valve (Transmission Hydraulic Control) - Test and Adjust".
If the pressure at the transmission hydraulic control relief valve is below the specification, the oil filter may be blocked and the oil filter bypass valve is not functioning. Remove the oil filter bypass valve and inspect the oil filter bypass valve for wear or damage.
If the pressure of the oil at the oil filter bypass valve is below the specification, the transmission oil pump is damaged or broken. The transmission oil pump is not serviceable and the transmission oil pump must be replaced.
Oil is supplied to the retarder from the torque converter outlet via the retarder hydraulic control valve. If the retarder is not functioning correctly, it is possible that the oil supply to the retarder is insufficient.
Test the pressure of the output from the retarder. Refer to Specifications, Systems Operation/Testing and Adjusting, "Power Train Pressures". If the pressure at the output from the retarder is incorrect, test the relief pressure at the torque converter outlet.
Note: When testing the pressure of the output from the retarder, the retarder must be engaged. Otherwise the pressure measured will be equal to the torque converter outlet pressure.
The relief valve for the torque converter outlet is located beneath the retarder hydraulic control valve. The relief valve for the torque converter outlet is used to maintain oil pressure in the torque converter. This allows the torque converter to transmit torque from the engine to the planetary transmission. If the relief pressure for the torque converter outlet is incorrect and the relief pressure for the torque converter inlet is correct, it will be necessary to replace the relief valve for the torque converter outlet. If the relief pressure for the torque converter outlet is correct, it is possible that the retarder hydraulic control valve is not functioning correctly. Refer to Specifications, Systems Operation/Testing and Adjusting, "Retarder - Test".