HARSH 3-2 DETENT DOWNSHIFT AT HIGH ALTITUDES- W/440-T4
Models Affected: 1988 BONNEVILLE WITH 440-T4 TRANSAXLE MODELS: 8BKH, 8BJH, 8BRH, 8BTH, 8BYH, 8FBH, 8FCH, 8FJH
BULLETIN COVERS:
A harsh 3-2 detent downshift that occurs at high altitudes for some 1988 Bonneville models 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 (#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 Information section.
SERVICE PARTS INFORMATION:
Transaxle Model 3-2 Control Identification Valve Spring (Figure 1) Package 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 1988 Bonneville Service Manual, Section 7Al Automatic Transaxle On Car Service and THM 440-T4 (ME9) Automatic Transaxle Unit Repair Table Of Contents for control valve assembly service information.
STATE OF ARIZONA STATE OF NEVAD --------------- --------------- APACHE NAVAJO CARSON CITY LANDER DOUGLAS LYON STATE OF COLORADO ELKO MINERAL ----------------- ESMERALDA STOREY ADAMS JEFFERSON EUREKA WHITE PINE ALAMOSA LAKE HUMBOLDT ARAPAHOE LA PLATA ARCHULETA LARIMER STATE OF NEW MEXICO BOULDER LAS ANIMAS ------------------- CHAFFEE LINCOLN BERNALILLO MORA CLEAR CREEK MESA CATRON RIO ARRIBA CONEJOS MINERAL COLFAX SANDOVAL COSTILLA MOFFAT CURRY SAN JUAN CROWLEY MONTEZUMA DE BACA SAN MIGUEL CUSTER MONTROSE GRANT SANTAFE DOLORES MORGAN GAUDALUPE SIERRA DELTA OURAY HARDING SOCORRO DENVER PARK LINCOLN TAOS DOUGLAS PITKIN LOS ALAMOS TORRANCE EAGLE PUEBLO LUNA UNION FREMONT ROUTT GARFIELD SAGUACHE STATE OF OREGON GILPIN SAN JUAN ---------------- GRAND SAN MIGUEL LAKE GUNNISON SUMMIT HINSDALE TELLER STATE OF UTAH HUERFANO WASHINGTON -------------- JACKSON WELD BEAVER PIUTE BOX ELDER RICH CACHE SALT LAKE STATE OF IDAHO CARBON SAN JUAN -------------- DAGGETT SANPETE BANNOCK CUSTER DAVIS SEVIER BEAR LAKE FRANKLIN DUCHESNE SUMMIT BINGHAM FREMONT EMERY TOOELE BLAINE JEFFERSON GRAND UINTAH BONNEVILLE MADISON IRON UTAH BUTTE MINIDOKA JUAB WASATCH CAMAS ONEIDA KANE WAYNE CARIBOU POWER MILLARD WEBER CASSIA TETON MORGAN CLARK VALLEY STATE OF WYOMING STATE OF MONTANA ----------------- ----------------- ALBANY NATRONA BEAVERHEAD MADISON CARBON NIOBRARA DEER LODGE MEAGHER CONVERSE PARK GALLATIN PARK FREEMONT PLATTE JEFFERSON SILVER BOW GOSHEN SUBLETTE HOT SPRINGS SWEETWATER STATE OF NEBRASKA JOHNSON TETON ----------------- LARAMIE UINTA BANNER SIOUX LINCOLN WESTON KIMBALL
*COUNTIES WHICH HAVE SUBSTANTIALLY ALL OF THEIR AREA ABOVE 4000 FT. REF. FEDERAL REGISTER, VOL. 42, NO. 76 APRIL 20, 1977, PG. 20464
Figure 3 - Designated High Altitude Counties*
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.
