Transaxle Refinements
TORQUE CONVERTERFor the 1991 model year, a damper assembly was added to the torque converter.
COOLER BYPASS VALVE
Reference: December 1989 Master Tech and TSB 21-16-90
An internal cooler bypass valve was introduced in July of 1990 for the 1991 model year which replaced the external cooler bypass valve introduced in December 1989. The cooler bypass is located in a bore in the pump face of the case. This can be seen by a bump in the case around the pump area near the cooler fittings. Always replace the bypass valve (P/N 4539880) during a transaxle overhaul.
TRANSFER SHAFT
Some early transfer shafts showed signs of torsional deflection under load in lab tests. There were no field failures. A thicker transfer shaft was used to correct this condition and prevent any possible pinion or ring gear failures. The change occurred in July of 1990 for the 1991 model year.
TRANSAXLE CASE
The case was modified for the 3.3L AWD minivans application in July 1990 for the 1991 model year. The extension housing was removed and the case was machined flat for the adapter plate installation. The adapter plate connects the transaxle to the power transfer unit. The outer differential carrier bearing was enlarged to handle the increased load.
INPUT SHAFT
The input shaft changed from a 24-tooth spline to a 22-tooth spline. The change in the amount of shaft splines was done to accommodate a newly designed torque converter and prevent incorrect assembly of the two components. The new torque converter was also designed with a damper assembly. The change covers the 1991-to-current models years.
INPUT CLUTCH RETAINER
The input clutch retainer has been changed to increase the depth of the reverse pressure plate snap ring groove by 0.5mm from 1 43.6mm diameter. There was no part number change. The change occurred in early 1990 for the 1991 model year and was done to increase snap ring retention and to ensure proper installation during the production process.
UNDERDRIVE/OVERDRIVE REACTION PLATE
Reference: TSB 21-03-91
An introduction hardening process was added to the underdrive/overdrive reaction plate for the 1991 model year. The increase in hardness improves durability of the plate and the underdrive/overdrive tapered snap ring. The hardening process may cause the plate to have black or dark lugs and a black or dark ring around the outer diameter of the part. This is a normal appearance and is not to be confused with a damaged or "burned up" plate. There are no dimensional changes to the plate. The four select part numbers were not changed.
TRANSAXLE FRICTION DISCS
Reference: TSB 21 -22-90
Improved friction discs are available for the overdrive and 2-4 clutches on the AWD 41AE production units and all clutches except the low/reverse for service units. The new friction material was included as a running change during the 1991 model year.
TRANSFER GEARS
Reference: TSB 21 -09-91 and 21 - 10 -91
New transfer gears were introduced as a running change in May of 1991. The output and transfer gear teeth have a new helix angle of 32 degrees to minimize gear whine. The prior production output and transfer gear teeth were at a 27.5 degree helix angle.
The recessed area on the output transfer gear has been eliminated to increase gear durability for 1991. The rear carrier output shaft is approximately 1/8" longer to accommodate the revised output gear. The output gear bolt and transfer shaft nut now have a Loctite material on the threads. The bolt and nut must be replaced whenever removed and not used for reassembly.
PRNDL SWITCH
Reference: TSB 21-01-91
If a vehicle built before May 1991 exhibits lighting of the backup lamps, clutch drag, slowing of the vehicle or vehicle shudder with the transaxle selector placed in the overdrive position, a faulty PRNDL Switch may be the cause. Diagnose and repair any diagnostic trouble codes that may be present and then follow the repair procedure for replacing the PRNDL Switch. The updated switch (July of 1991) can be identified by the antique bronze/olive drab appearance of the switch housing.
VALVE BODY
A new valve body was released inlay of 1991 which contains aluminum spool valves for reduced leakage throughout the temperature range. The prior steel spool valves could potentially leak because of the difference in thermal expansion of steel valves in an aluminum housing. The new valve body also contains a different converter clutch control valve that provides for Electronically Modulated Converter Clutch (EMCC). The old valve was referred to as the lock-up switch valve.
In August of 1991, a steel regulator valve was introduced to reduce the tendency to buzz in reverse gear range. A steel valve provides increased valve stability.