3RD FLUID REROUTE FOR POSSIBLE HARSH 3-2 DOWN. AT HIGH ALT.

TRANSMISSION APPLICATIONS: SUBJECT:

1990 3T40 (125C) HARSH 3-2 DOWNSHIFT AT HIGH ALTITUDE

TRANSMISSION MODELS: VEHICLE APPLICATIONS:

1990 A AND N SERIES CARS

Bulletin Covers:(Refer to Figure 1)

New 3rd fluid reroute of 3-2 downshift fluid for a more consistent 3-2 downshift feel at high altitude areas. This consists of a new 3rd clutch fluid with external bracket, and modification of the control valve assembly and auxiliary valve body and gasket to allow a faster flow of 3rd signal fluid to the 3rd fluid switch during 3-2 downshifts while maintaining 3rd 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 3rd clutch fluid, control valve assembly, auxiliary valve body and gasket went into production for OBUC, OBYC, OBZC HYDRA-MATIC 3T40 (THM 125C) transaxles Start of Production 1990.

SERVICE PROCEDURE:

Do not attempt to use the new 3rd 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 3rd 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 3rd Clutch Fluid with Bracket

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.

General Motors bulletins are intended for use by professional technicians, not a "do-it-yourselfer". They are written to inform those technicians of conditions that may occur on some vehicles, or to provide information that could assist in the proper service of a vehicle. Properly trained technicians have the equipment, tools, safety instructions and know-how to do a job properly and safely. If a condition is described, do not assume that the bulletin applies to your vehicle, or that your vehicle will have that condition. See a General Motors dealer servicing your brand of General Motors vehicle for information on whether your vehicle may benefit from the information.