A/T - THM 440-T4 Harsh or Firm 2-3 Upshifts.
89buick06Bulletin 87-7440-18
Date April '89
Ref. No. 87-237-7440
Corp. Ref. No. 977108
SUBJECT: HARSH OR FIRM 2-3 UPSHIFTS
MODELS AFFECTED: 1986 SRTA UNITS, AND 1987 CENTURYS, LESABRES, ELECTRAS, AND RIVIERAS EQUIPPED WITH A THM 440-T4 HYDRA-MATIC 4T60 TRANSAXLE AND 3.8L ENGINE (VIN CODE 3)
Figure 1 - THM 440-T4 Transaxle Identification Information:
BULLETIN COVERS: (Figure 1)
A harsh or firm 2-3 upshift that may occur most noticeably under 1/2 throttle acceleration on 1986 SRTA models and 1987 Centurys, Electras, Rivieras, and LeSabres equipped with a 3.8L and THM 440-T4/Hydra-matic 4T60 transaxle. This condition can be corrected by following the procedure listed under "Service Action".
Figure 2 - 3-4 MTV And 2-3 Accumulator Valve Trains:
SERVICE ACTION:
1. Verify correct minimum and maximum pressures.
2. Check for vacuum leaks and/or a low vacuum supply to the vacuum modulator. Required vacuum is 44-61 KPa (13-18 in. Hg.). The vacuum signal should respond quickly to throttle movement; if not, check for anything that could cause a vacuum restriction to the modulator causing a delayed response to throttle movement, like paint in the modulator tube and/or carbon at the throttle body fitting.
3. Remove the 3-4 M.T.V. Bushing (338), 2-3 Accumulator Valve (337), then the 2-3 Accumulator Spring (336) as shown in Figure 2. Install the 2-3 Accumulator Spring (336) from the appropriate service package shown in the "Service Parts Information" section.
While the transaxle is disassembled, check the items listed below that affect transaxle operation which may also contribute to the harsh shift condition.
- # 7 Check Ball and Capsule for leaks.
- 1-2 Servo Pipe for leaks.
- 1-2 Servo for seal damage or binding.
- # 12 Check Ball missing, or mislocated.
- Spacer Plate for peening from Check Balls # 4 and # 12.
Figure 1 - THM 440-T4 Transaxle Identification Information:
SERVICE PARTS INFORMATION:
Transaxle Model 2-3 Accumulator
Identification Spring Package
(Figure 1) Number Contents
6FBH, 7FBH, 8662972 (1) Spring, 2-3 Accumulator
7FKH (2) Spacer Plate Gaskets
(1) Instruction Sheet
6FCH, 6FZH 8662973 (1) Spring, 2-3 Accumulator
7FCH, 7FZH (2) Spacer Plate Gaskets
(1) Instruction Sheet
6FTH, 6FYH 8662977 (1) Spring, 2-3 Accumulator
7FNH, 7FRH, (2) Spacer Plate Gaskets
7FTH (1) Instruction Sheet
Parts are currently available from GMSPO.
SERVICE MANUAL REFERENCE:
Refer to the appropriate 1986 or 1987 Service Information Manual, Section 7A1 Automatic Transaxle On Car Service and THM 440-T4/HYDRA-MATIC 4T60 (ME9) Automatic Transaxle Unit Repair Table of Contents for Control Valve Assembly service information.