VIBRATION/DRONE NOISE BETWEEN 1700-1900 RPM WITH TCC LOCKED. GMC Truck GMC G Van 1994

REVISION: 06/06/96

THIS BULLETIN IS BEING REVISED TO UPDATE THE NEW SCAN I.D. NUMBERS IN THE PARTS INFORMATION CHART. PLEASE DISCARD BULLETIN 67-71-44 (SECTION 7-TRANSMISSION). ---------------------------------------------------------------------- SUBJECT: VIBRATION/DRONE NOISE BETWEEN 1700-1900 RPM WITH TCC LOCKED (REPLACE THE EPROM)

MODELS: 1993-95 CHEVROLET AND GMC G VANS WITH A 6.2L OR 6.5L DIESEL ENGINE (VINS J,Y - RPOS LL4,L57) AND HYDRA-MATIC 4L80-E AUTOMATIC TRANSMISSION (RPO MT1)

TRANSMISSION MODELS: 3KDP, 3KFP, 3PAP, 3PBP, 4HAP, 4HCP, 4LAP, 4LBP, 5ALP, 5LAP

CONDITION:

A DRIVELINE VIBRATION OR DRONE TYPE NOISE IS HEARD THROUGHOUT THE VEHICLE WHEN THE ENGINE IS BETWEEN 1700-1900 RPM WITH THE TORQUE CONVERTER CLUTCH (TCC) APPLIED.

CAUSE:

ENGINE FIRING PULSES ARE TRANSMITTED THROUGH THE DRIVELINE CREATING A VIBRATION/DRONE NOISE.

CORRECTION:

IF NORMAL DIAGNOSIS FAILS TO DETERMINE THE CAUSE OF THE CONCERN, REPLACE THE EPROM.

SERVICE PROCEDURE REFER TO THE APPROPRIATE SERVICE MANUAL FOR THE EPROM REPLACEMENT PROCEDURE.

THE SERVICE EPROM WILL RAISE THE TCC APPLY SPEED TO 59 MPH (95 KPH) AND THE COAST DOWN TCC RELEASE SPEED TO 57 MPH (92 KPH). THIS EPROM MAY EFFECT FUEL ECONOMY.

IMPORTANT: THE VIBRATION/DRONE NOISE IS CAUSED BY NORMAL ENGINE VIBRATIONS BEING TRANSMITTED THROUGH THE DRIVELINE TO THE BODY OF THE VEHICLE. WHEN THE TORQUE CONVERTER CLUTCH IS APPLIED, THE FLUID COUPLING NO LONGER ABSORBS THE ENGINE VIBRATION. THE TRANSMISSION TORQUE CONVERTER SHOULD NOT BE REPLACED IF A VIBRATION/SHUDDER CONDITION EXISTS AFTER THE TCC IS APPLIED.

PARTS INFORMATION:

PREVIOUS PREVIOUS NEW EPROM NEW NEW BROADCAST SCAN PART BROADCAST SCAN CODE I.D. NUMBER CODE I.D.

1993 BFDS 7069 16239124 BUYT 9119 1994 BCYH 4229 16236763 BUFW 6779 1994 BJDL 7359 16236763 BUFW 6779 1995 BKUJ 3139 16236765 BUFX 6789

PARTS ARE CURRENTLY AVAILABLE FROM GMSPO.

WARRANTY INFORMATION FOR VEHICLES REPAIRED UNDER WARRANTY, USE:

LABOR OPERATION: T0500 0.3 HOURS

FIGURES: 0 ATTACHMENTS: 0

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