III. TCC Operation

A. Converter Clutch Apply Valve - Determines the method of oil feed to the torque converter to engage or disengage the clutch mechanism. The apply valve is located in the pump assembly on THM 200-4R transmissions and in the caser assembly on THM 325-4L transmissions.

FIGURE 2 - Converter Clutch Released (THM 200-4R Shown - THM 325-4L Typical):

B. Converter Clutch in Released Position (refer to Figure 2) - When the TCC solenoid is not energized, converter signal oil is exhausted allowing the converter clutch apply valve spring to hold the apply valve in the release position. The apply valve in this position takes converter feed oil and sends it into the release passage, and into the cavity between the converter clutch pressure plate and the converter cover. This moves the clutch pressure plate away from the converter cover, releasing the converter clutch.

After the oil releases the converter clutch, it flows from behind the pressure plate and through the converter. From the converter, the oil flows backwards through the apply passage to the apply valve. The apply valve then sends oil, returning from the converter, to the transmission cooler in the radiator. Oil, returning from the cooler, is then directed to the transmission lubrication system.

FIGURE 3 - Converter Clutch Applied (THM 200-4R Shown - THM 325-4L Typical):

C. Converter Clutch in Applied Position (refer to Figure 3) - When enable conditions are met the ECM grounds circuit 422 and energizes the TCC solenoid. With the solenoid energized signal off is not allowed to exhaust and overcomes the converter clutch apply valve spring, shifting the valve and changing the direction of the converter feed off. The converter clutch apply valve will now send converter feed oil into the apply passage. The apply off will charge the converter with oil and force the converter clutch pressure plate against the converter cover, causing a mechanical link between the engine and transmission. At the same time the converter clutch apply valve will direct some converter feed off through an orifice to the transmission cooler in the radiator. Oil returning from the cooler, is then directed to the transmission lubrication system.

On early 1982 Cadillacs, a converter clutch shift valve and converter clutch TV valve were also in the control valve assembly. These valves were designed to control the speed at which the TCC would apply. Since TCC apply speed is controlled by the ECM on Cadillacs equipped with HT4100 engines, the converter clutch shift valve and converter clutch TV valve were no longer necessary and, therefore, eliminated. For further information regarding the elimination of these valves, refer to Serviceman Bulletin 84-25, Group 7, No. 91.