Theory of Operation of New Components

Servo Apply Valve





The servo apply valve, located in the valvebody is used to control reverse apply oil to the forward/reverse servo piston. When reverse is selected, the manual valve will allow oil to be applied to the servo apply valve. If vehicle speed input to the PCM indicates the vehicle is less than 8 km/h (5 mph), then the dog clutch can be moved to the reverse direction without causing damage. With vehicle speed less than 8 km/h (5 mph), and reverse selected, the PCM will command high-line pressure. When high-line pressure is commanded, the pressure will move the servo apply valve against the spring which opens up the passage allowing oil to pass through the servo apply valve to the forward/reverse servo piston.





Refer to Figure 6 showing hydraulic schematic while in Reverse.

If reverse is selected when vehicle speed is greater then 8 km/h (5 mph), the PCM will command low-line pressure causing the servo apply spring to keep the passage in the servo apply valve closed, preventing oil to reach the forward/reverse servo piston. This action does not allow the dog clutch to move, thus preventing internal damage to the transaxle.

Spacer Plate and Spacer Plate Gasket





The spacer plate and spacer plate gaskets are redesigned to accommodate the new valvebody. The 1992 2nd design parts will contain an identification mark as shown in Figure 7.

Forward/Reverse Servo Piston And Spring








In addition to the servo valve previously described, the forward/reverse servo piston and spring have been redesigned. The main difference in the new piston is that the step and a hole in the shaft have been eliminated. Also, the spring in the new design is longer. Figures 8 and 9 show the differences.

Transaxle Case Assembly

Due to the elimination of the step in the forward/reverse servo piston, the case has been redesigned to accommodate the removal of this step.

IMPORTANT:
The new case can be identified by a "SV," located on the casting below the case-to-cradle mount holes.

Manual Valve

Due to valvebody changes, the manual valve has also been redesigned for directing oil to the proper hydraulic circuits. The new manual valve is illustrated in Figure 10. The new valve will have a slot instead of a flat near the end which connects the valve to the linkage.

IMPORTANT:
When installing the 2nd designed manual valve, the notch must be facing up.

Powertrain Control Module

In addition to changes in the transaxle, there are changes in the PCM which make a new PCM a requirement. The new PCM cannot be used on previous models. The logic for preventing dog clutch engagement when the vehicle speed is present has been added, and the most noticeable change is that under certain drive/idle conditions, low-line pressure or high pressure line will be commanded. This change will eliminate the actuator buzzing noise detected while at idle and when the transaxle is in drive.