Transaxle Refinements
OVERDRIVE/REVERSE PISTONReference: December 1989 Master Tech and TSB 21-09-90 (Rev. A)
In July of 1989, for 1990-1/4 production, the eight-slot OD/Rev piston and pressure plate assembly was upgraded to a four-slot piston and pressure plate assembly.
The OD/Reverse piston orifice production procedure was revised in December of 1989 for 1990. The staking process and the length of the orifice assembly were changed to prevent reverse and overdrive clutch failures due to orifice blow-out or incorrect orifice installation.
LOW/REVERSE PISTON RETAINER
Reference: TSB 21-09-90 (Rev. A)
Transaxles that experienced a "stop bump" (harsh initial or coastdown engagement) condition may have been the result of a high surface finish on the low/reverse clutch piston retainer first discovered in February 1990. The out-of-specification surface finish of the retainer could cause the low/reverse lip seal to wear and not energize until the TCM recognized that the shift was not completed in the specified time. The TCM would then turn, the solenoid controlling the L/R clutch circuit, to full "ON". This would apply full line pressure to the clutch. The result was the "stop bump" condition.
TRANSAXLE SNAP RINGS
Reference: HL-07-90
In March of 1990, the tapered snap ring on the input clutch hub was modified for installation purposes. The tab on the left side of the snap ring was thickened to make sure that the snap ring was installed with the taper up.
TORQUE CONVERTER
A 10" torque converter an additional improvement by bonding friction material to front cover was introduced for the 3.3L and 3.8L applications. This was upgraded from a 9.5" converter. The larger converter was needed to handle the increased torque load of the larger engines and was introduced in June 1990. Current part number is 4736076.
INPUT CLUTCH ASSEMBLY
Reference: December 1989 Master Tech
In 1989, the input clutch assembly and retainer was upgraded to enhance durability and quality, for the 1990 model year. The overdrive clutch changed from a 3-disc, 2-separator plate assembly to a 4-disc, 3-separator plate assembly.
PRNDL SWITCH
Reference: TSB 21-07-90
The production process for this switch changed in January 1990, and as a result, improved the internal contacts of the PRNDL Switch.
INPUT CLUTCH HUB BUSHING
Reference: TSB 21 -24-90
The surface finish of the reaction shaft support journal could cause excessive wear of the input clutch hub housing. The reaction shaft and the input clutch hub machining process was revised in August of 1990 to improve wear.
OVERDRIVE/REVERSE PISTON
Reference: HL-17-91
The OD/Rev piston has had material removed between the pressure plate snap rings. The material is not needed and the change reduces the weight of the OD/Rev piston and allows easier snap ring installation. This change occurred during 1990 production.
UNDERDRIVE/OVERDRIVE REACTION PLATE
The underdrive/overdrive reaction plate was revised as a running change during December 1990. The new plate is different in appearance from the parts that were used during production in prior years. The new plate is fully compatible with all other parts in the input clutch assembly. However, the plate must be used with a matched snap ring. A mismatch of these components can cause the plate to move, resulting in a 2-3 upshift shudder and/or a harsh 4-3 downshift.
LOW/REVERSE CLUTCH
When measuring to change low/reverse clutch pack clearance, a reduction in clearance (0.035") can substantially improve 2/1 shift quality.
PISTON LIP SEAL
For 1990 and later, the underdrive clutch piston large outer lip seal is shallower. This lip seal cannot be used with previous 1989 input clutch retainers.
TRANSMISSION CONTROL MODULE
Reference: See TSB 18-24-95