A/T - Harsh 3-2 Downshift at High Altitude

9224buick02

Bulletin
90-7125-2

Date
Oct., '89

Ref. No.
90-013-7125

Corp. Ref. No.
977142R


SUBJECT:
THIRD CLUTCH FLUID REROUTE FOR POSSIBLE HARSH 3-2 DOWNSHIFT AT HIGH ALTITUDE - 1990 CENTURY AND SKYLARK MODELS WITH 3T40 (125C) AND 3.3L ENGINE


MODELS AFFECTED:
1990 CENTURY AND SKYLARK





BULLETIN COVERS (Refer to Figure 1)

New third clutch fluid reroute of 3-2 downshift fluid for a more consistent 3-2 downshift feel at high altitude areas. This consists of a new third clutch switch with external bracket, and modification of the control valve assembly and auxiliary valve body and gasket to allow a faster flow of third clutch signal fluid to the third clutch switch during 3-2 downshifts while maintaining third clutch fluid to the orifice control valve.

These new castings, with appropriate machining differences, are also used on all other models. The auxiliary valve body gasket revision applies to all auxiliary body gaskets.








DATE OF PRODUCTION CHANGE (Refer to Figure 2)

The new third clutch switch, control valve assembly, auxiliary valve body and gasket went into production for 0BUC, 0BYC, 0BZC HYDRA-MATIC 3T40 (THM 125C) transaxles at Start of Production 1990.

SERVICE PROCEDURE

Do not attempt to use the new third clutch fluid reroute components on any other prior or current model year HYDRA-MATIC 3T40 (THM 125C) transaxle since the parts are not interchangeable, or a change in shift characteristics and/or unit durability will occur.





SERVICE PARTS INFORMATION

Whenever ordering parts for models equipped with the new third clutch fluid reroute, refer to the following part numbers:

Part Number Package Description

8666385 BUC Control Valve Assembly with
8666384 BYC, BZC Auxiliary Valve Body
8666380 Auxiliary Valve Body Gasket
8666603 Third Clutch Fluid Switch with Bracket

Parts are currently available from GMSPO.

SERVICE MANUAL REFERENCE

Whenever servicing any HYDRA-MATIC 3T40 (THM 125C) (MD9) transaxle, refer to the procedures outlined in the Unit Repair Section of your Service Manual.