Figure - 1 Previous And New Model Alpha Codes:

The shift speed charts, minimum and maximum oil pressures and wiring diagrams have not changed. Use the cross-reference chart in Figure 1 to find the previous 1990 model; then reference previous model data listed (oil pressure, wiring diagrams and shift speed charts) to service the new 1990 model. For example, the new 1990 model OWMH will be serviced by the 1990 OBHH model data.

Figure - 2 Previous And New Input Clutch Components:

For the new channel plate, input clutch wave plate and input clutch plate, the following parts were modified to eliminate the input accumulator components:

Four instead of three input clutch (steel or reaction) plates (647). The new input clutch plate will assemble between the added wave plate (810) and input clutch (fiber) plate assembly (The new input clutch plates will also be thinner by 0.722 mm (0.028") to make room for the added wave plate and input clutch plate). The previous input clutch plates will still be available. Do not mix the previous and new input clutch plates; this will cause a durability concern.

Figure 3 - Eliminated And New Components For Channel Plate:

Channel plate (404) will not have the input clutch accumulator bore and components. A wave plate will be added to the input clutch assembly that will replace the function of the accumulator. The new channel plate will also have porting changes that will help ensure that two ports will never be opened simultaneously, which causes distress to the 4th clutch assembly when the shift cable is not set correctly or is kinked or binding. The previous channel plate with the input accumulator bore and components and the new channel plate are not interchangeable. The channel plate with the input accumulator will still be available.

Figure 4 - Manual Valve:

New manual valve (403) will have changes to the valve lands and be reduced 0.25 mm (0.010") in diameter for the new porting changes to the channel plate. The previous and new manual valves are not interchangeable. The new manual valve will assemble into the previous production channel plate, but the transaxle will not function because of excessive leakage due to the differences in sizes.

Figure 5 - Detent Lever:

New inside detent lever (704) will have the manual link hole location changed for a different "throw" of the manual valve. The previous and new inside detent lever are not inter-changeable even though the parts will physically assemble. The new inside detent lever must be used with the new manual valve and channel plate. The previous inside detent lever must be used with the previous manual valve and channel plate. The identifier for the new Grand Prix inside detent lever is an added square hole. The previous Grand Prix inside detent lever is gold in color. Some of the early new Grand Prix inside detent levers may be gold in color and have the added square hole. The gold color will be discontinued and the square hole will be the only identifier for the new Grand Prix inside detent lever. The previous inside detent lever will still be available for models that just need replacement of the lever for 1987 and prior model years.

Figure 6 - Previous And New Input Housings:

Input housing (632) has been revised by moving the snap ring groove up 1.50 mm (0.059") to make room for the wave plate and extra input clutch plate in the input clutch. The previous and new input housings are not interchangeable because of the differences in clutch pack free play and travel. The previous input housing will still be available.
DATE OF PRODUCTION CHANGE:

All HYDRA-MATIC 4T60 (THM 440-T4) transaxles are built with the new channel plate, input housing (with the wave plate and extra input clutch plate) and new model codes starting January 16, 1990 (Julian Date 016).

SRTA MODEL INFORMATION:

SRTA models with the new 1990 model codes may not have all the new components listed in this Service Bulletin. These parts include: new input housing with the wave plate and four thinner input clutch plates and the new production channel plate without the input accumulator components.

SERVICE PARTS INFORMATION:

The channel plate assembly packages will contain:

- Channel plate assembly without input clutch accumulator bore
- Valve, manual