Century Estate Wagon V6-231 3.8L (1985)
Shift Modulator: All Technical Service Bulletins
Harsh Upshifts - High Altitude Only
VI. HARSH UPSHIFTS - HIGH ALTITUDE ONLY
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1985-86 Century models with 2.8L engines
Service Procedure:
Harsh upshifts for ALL GEARS at high altitudes may be caused by high line pressure due to low engine vacuum. This condition may be corrected on
certain transaxle models by installing the appropriate aneroid modulator Service Package.
Service Parts Information:
Service Package
Transaxle Model Identification
Number
8646956
6CFH, 6CMH, 6HBH, 6HJH
5CM, 5CN, 5CP, 5CW, 5HA, 5HJ, 5HT
8646966
6AAH, 6ACH, 6AFH, 6AMH
5AF, 5AM
8646967
6ADH, 6ARH
Parts are currently available from GMSPO.
Service Notes:
A new vacuum line from the engine to the vacuum modulator MUST also be installed when using the service packages listed above.
Part Number
Vehicle Application
14062624
Century
Parts are currently available from GMSPO.
Other items affecting harsh upshift conditions are:
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engine vacuum leaks
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sticking modulator valve
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restrictions in the vacuum lines such as paint in the modulator tube and/or carbon at the throttle body fitting
Transaxle Identification Information
