For 1990-2009 cars

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

#### 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 OBUC, OBYC, OBZC 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 vear 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.

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.