HARSH 3-2 DETENT DOWNSHIFT AT HIGH ALTITUDES- W/440-T4

SUBJECT: HARSH 3-2 DETENT DOWNSHIFT AT HIGH ALTITUDES

MODELS/YEARS: 1988 MODELS EQUIPPED WITH 440-T4 TRANSAXLE (RPO - ME9)

This bulletin covers harsh 3-2 detent downshift that occurs at high altitudes for some 1988 A, C, E and H cars equipped with a 3.8L or 3800 engine and a THM 440-T4 transaxle. This condition may be corrected by replacing the 3-2 control valve spring (341) shown in Figure 2. Refer to Figure 3 for areas designated as High Altitude Counties in the continental United States.

Prior to replacing the 3-2 control valve spring, other items to be inspected that affect transaxle operation and may contribute to harsh shift conditions are:

- vacuum leaks (low vacuum supply to the vacuum modulator). Required vacuum is 44-61 kPa (13-18 in. Hg.)

- paint in the modulator tube restricting vacuum to the modulator causing a delayed response to throttle movement.

- sticking modulator valve

- sticking 1 -2 servo valve

- missing checkball (no. 2, 4 or 12)

SERVICE ACTION:

Remove the control valve assembly from the transaxle and disassemble the 3-2 control valve train. Install the 3-2 control valve spring (341) from the appropriate service package shown in the Service Parts I nformation section.

SERVICE PARTS INFORMATION:

Transaxle Model 3-2 Control Valve Identification Spring Package (Figure 1) Number Contents ---------- ------ -------- 8FCH 8646979 (1) 3-2 Control Valve Spring (2) Spacer Plate Gaskets (1) Instruction Sheet

8BKH, 8FBH 8646982 (1) 3-2 Control Valve Spring (2) Spacer Plate Gaskets (1) Instruction Sheet

8BJH, 8BRH 8646993 (1) 3-2 Control Valve Spring 8BTH, 8BYH (2) Spacer Plate Gaskets 8FJH (1) Instruction Sheet

Parts are currently available from GMSPO.

SERVICE MANUAL REFERENCE:

Refer to the appropriate 1988 Service Information Manual. Section 7A1 Automatic Transaxle On-Car Service and THM 440-T4 (ME9) Automatic Transaxle Unit Repair Table of Contents for control valve assembly service information.

FIGURE 3 - DESIGNATED HIGH ALTITUDE COUNTRIES*

STATE OF ARIZONA STATE OF NEVADA ---------------- ----------------- Apache Navajo Carson City Lander Douglas Luon STATE OF COLORADO Elko Mineral ----------------- Esmeralda Storey Adams Jefferson Eureka White Pine Alamosa Lake Humboldt Arapahoe La Plata Archuleta Larimer Boulder Las Animas STATE OF NEW MEXICO Chaffe Lincoln ------------------- Clear Creek Mesa Bernalillo Mora Conejos Mineral Catron Rio Arriba Costilla Moffat Colfax Sandoval Crowley Montezuma Curry San Juan Custer Montrose De Baca San Miguel Dolores Morgan Grant Sierra Delta Ouray Gaudaluipe Sierra Denver Park Harding Socorro Douglas Pitkin Lincoln Taos Eagle Pueblo Los Alamos Torrance Elbert Rio Blanco Luna Union El Paso Rio Grande McKinley Valencia Fremont Routt Garfield Saguache STATE OF OREGON Gilpin San Juan ---------------- Grand Sam Miguel Lake Gunnison Summit Hinsdale Teller STATE OF UTAH Juerfano Washington -------------- Jackson Weld Beaver Piute Box Elder Cache Rich STATE OF IDAHO Carbon Salt Lake ------------- Daggett San Juan Bannock Custer Davis Sanpete Bear Lake Franklin Dushesne Sevier Bingham Fremont Emery Summit Blaine Jefferson Grand Tooele Bonneville Madison Iron Uintah Butte Minidoka Juab Utah Camas Onieda Kane Wasatch Caribou Power Millard Wayne Cassia Teton Morgan Weber Clark Valley

STATE OF MONTANA STATE OF WYOMING ---------------- ---------------- Beaverhead Madison Albany Natrona Deer Lodge Meagher Carbon Niobrara Gallatin Park Converse Park Jefferson Silver Bow Freemont Platte Goshen Sublette STATE OF NEBRASKA Hot Springs Sweetwater ----------------- Johnson Teton Banner Laramie Uinta Kimball Lincoln Weston Sioux

* Countries which have substantially all of their area above 4000 ft. Ref. Federal Register, Vol. 42, No. 76 April 20, 1977, Pg. 20464

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.