CAMPAIGN: AUTO TRANSMISSION MODULATOR VALVE IS INCORRECT

CAMPAIGN NUMBER: 90C15 GROUP: 7A-AUTOMATIC TRANSMISSION

SUBJECT: AUTOMATIC TRANSMISSION MODULATOR VALVE INCORRECT

MODELS: 1990 C5H, C6H, C7H TOPKICK/KODIAK EQUIPPED WITH ALLISON AUTOMATIC TRANSMISSION AT545 (RPO MF1) AND GASOLINE ENGINES 366 CU.IN. (RPO LS0) OR 427 CU.IN. (RPO LR0)

DEFECT INVOLVED

CERTAIN TOPKICK/KODIAK MEDIUM TRUCKS EQUIPPED WITH GASOLINE ENGINES AND ALLISON AT545 AUTOMATIC TRANSMISSIONS MAY EXHIBIT BOTH EARLY UPSHIFTS AND LATE DOWNSHIFTS. THIS IMPROPER SHIFTING IS CAUSED BY AN INCORRECT PISTON IN THE TRANSMISSION VACUUM MODULATOR VALVE.

TO CORRECT THIS CONDITION IT WILL BE NECESSARY TO INSPECT THE PISTON IN THE MODULATOR VALVE TO SEE IF IT IS CORRECT, AND REPLACE THE VALVE IF NECESSARY.

VEHICLES INVOLVED

INVOLVED ARE CERTAIN 1990 C5H, C6H, C7H TOPKICK/KODIAK MEDIUM TRUCKS BUILT WITHIN THE FOLLOWING VIN BREAKPOINTS:

FROM THROUGH

GMC TRUCK TOPKICK LJ603028 LJ606222 CHEVROLET KODIAK LJ201302 LJ202364

THERE ARE A TOTAL OF 88 VEHICLES INVOLVED IN THIS CAMPAIGN. (TOTAL CHANGED FROM 95, AS ORIGINALLY STATED IN DCS MESSAGE.)

OWNER NOTIFICATION

THERE WILL BE NO OWNER LETTER SENT OUT WITH THIS CAMPAIGN, AS IT IS ANTICIPATED THE VEHICLES WILL EITHER BE IN DEALER STOCK OR AT A BODY BUILDERS. IF A UNIT HAS BEEN RETAILED, IN ORDER TO MAINTAIN CUSTOMER SATISFACTION, CONTACT THE OWNER AND ARRANGE TO HAVE THE VEHICLE INSPECTED AND IF REQUIRED, A NEW MODULATOR VALVE INSTALLED.

SERVICE INFORMATION

ALL INVOLVED UNITS MUST BE INSPECTED FOR THE CONDITION AND CORRECTED IF NECESSARY. IT WILL BE NECESSARY TO PERFORM THE FOLLOWING PROCEDURE TO DETERMINE IF A VEHICLE HAS AN INCORRECT VACUUM MODULATOR:

. REMOVE THE VACUUM MODULATOR RETAINING STRAP BOLT.

. REMOVE THE VACUUM MODULATOR.

. VISUALLY INSPECT THE TRANSMISSION END OF THE VACUUM MODULATOR TO INSURE THAT THE VACUUM MODULATOR PLUNGER DOES NOT HAVE A HOLE IN THE CENTER.

. IF A HOLE IS FOUND, INSTALL A NEW VACUUM MODULATOR.

. IF A HOLE IS NOT FOUND, REINSTALL THE ORIGINAL VACUUM MODULATOR, AS THIS IS THE CORRECT VALVE.

SERVICE PROCEDURE FOR INSTALLATION OF THE CORRECT TRANSMISSION VACUUM MODULATOR IS DESCRIBED IN THE 1990 TOPKICK/KODIAK MEDIUM TRUCK SERVICE MANUAL, X9033. REFERENCE SECTION 7A-15 AUTOMATIC TRANSMISSION, FOR VACUUM MODULATOR REPLACEMENT.

PARTS INFORMATION

PARTS ARE TO BE OBTAINED FROM GENERAL MOTORS SERVICE PARTS OPERATION (GMSPO). TO ENSURE THAT THESE PARTS WILL BE OBTAINED AS SOON AS POSSIBLE, THEY SHOULD BE ORDERED FROM GMSPO ON A C.I.O. ORDER WITH NO SPECIAL INSTRUCTION CODE BUT ORDER UNDER AN ADVISE CODE (2).

PART NUMBER DESCRIPTION QUANTITY

23048272 VACUUM MODULATOR KIT 1

IT IS ANTICIPATED THAT APPROXIMATELY 50% OF ALL INVOLVED VEHICLS MAY NEED MODULATOR REPLACEMENT.

WARRANTY INFORMATION

DEALERS SHOULD SUBMIT AN ACCURATELY FILLED OUT WARRANTY REPAIR ORDER ON EACH VEHICLE COMPLETED UNDER THIS CAMPAIGN.

LABOR OPERATION *TIME TROUBLE NUMBER DESCRIPTION ALLOWANCE CODE

V6080 INSPECT MODULATOR VALVE 0.2 HR. 96 FOR CORRECT PISTON. REPLACE MODULATOR IF REQUIRED.

*FOR DEALER TO RECEIVE ADMINISTRATIVE TIME ALLOWANCE ASSOCIATED WITH THIS CAMPAIGN, ADD 0.1 HOUR TO THE LABOR OPERATION TIME ALLOWANCE.

CAMPAIGN IDENTIFICATION LABEL

EACH VEHICLE CORRECTED IN ACCORDANCE WITH THE INSTRUCTIONS OUTLINED IN THIS CAMPAIGN WILL REQUIRE A "CAMPAIGN IDENTIFICATION LABEL". EACH LABEL PROVIDES A SPACE TO INCLUDE THE CAMPAIGN NUMBER AND THE FIVE (5) DIGIT DEALER CODE OF THE DEALER PERFORMING THE CAMPAIGN SERVICE. THIS INFORMATION MAY BE INSERTED WITH A TYPEWRITER OR BALL POINT PEN.

EACH "CAMPAIGN IDENTIFICATION LABEL" IS TO BE LOCATED ON THE RADIATOR CORE SUPPORT IN AN AREA WHICH WILL BE VISIBLE WHEN THE VEHICLE IS BROUGHT IN FOR PERIODIC SERVICING BY THE OWNER.

APPLY "CAMPAIGN IDENTIFICATION LABEL" ONLY ON A CLEAN, DRY SURFACE.

ADMINISTRATIVE PROCEDURE

PROCEDURES COVERING THIS CAMPAIGN ARE OUTLINED IN SECTION V OF YOUR DEALERSHIP'S "GM TRUCK CLAIMS PROCESSING MANUAL" #P8919.

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.