A/T - Harsh 3-2 Gear Detent Downshift at High Altitudes
88buick18Bulletin 88-7440-10
Date Sept. '88
Ref. No. 88-229-7440
Corp. Ref. No. 877135R
SUBJECT: HARSH 3-2 DETENT DOWNSHIFT AT HIGH ALTITUDES
MODELS AFFECTED: 1988 VEHICLES EQUIPPED WITH A THM 440-T4 (ME9) TRANSAXLE
FIGURE 2 - 3-2 CONTROL VALVE LINE UP:
FIGURE 3 - DESIGNATED HIGH ALTITUDE COUNTIES*:
BULLETIN COVERS
A 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 (#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.
FIGURE 1 - THM 440-T4 TRANSAXLE IDENTIFICATION INFORMATION:
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.