A/T - Erratic or No Upshift (New Governor Driven Gear)
88chevy06GMC NUMBER: 88-T-99
GROUP: 7A - Automatic Transmission
DATE: March, 1988
CORPORATE
NUMBER: 877123
SUBJECT: ERRATIC OR NO UPSHIFT (NEW GOVERNOR DRIVEN GEAR)
MODELS: 1978-1988 L/D VEHICLES EQUIPPED WITH THM 400/475 (M40/M41) AUTOMATIC TRANSMISSION 1982-1988 L/D VEHICLES EQUIPPED WITH THM 700 R4 (MD8) AUTOMATIC TRANSMISSION
FIGURE 1 - "APPLECORED" GOVERNOR DRIVEN GEAR:
BULLETIN COVERS:
A THM 400/475 or 700-R4 transmission with an erratic or no upshift condition which may be due to applecoring of the governor driven gear. "Applecoring" of the governor driven gear (refer to Figure No. 1) may be caused by nicks and/or buffs on the governor drive gear. The new governor driven gear has a higher fiberglass content. Also, inspect the output shaft for nicks and/or burrs on the governor drive gear. Replace the output shaft if nicks and/or buffs are found.
FIGURE 2 - THM 400/700-R4 TRANSMISSION IDENTIFICATION INFORMATION:
DATE OF PRODUCTION CHANGE: (Figure No. 2)
Beginning December 11, 1987 (Julian Date 345) all THM 400/475 transmissions were produced with the new governor driven gear. Beginning July 6, 1987 (Julian Date 187) all THM 700-R4 transmissions were produced with the new governor driven gear.
SERVICE ACTION:
When servicing any THM 400/475 governor driven gear, use the new governor driven gear and pin package listed under "Service Parts Information".
When servicing any THM 700-R4 governor driven gear for an "applecored" condition, use the new governor driven gear and pin package listed under "Service Parts Information". NOTE: The new THM 700-R4 governor gear is green in color (the previous gear was blue.) This can be used as another method of identification. When servicing any 1982 through 1986 THM 700-R4 govemor driven gear for conditions other than applecoring, the previous governor driven gear, package number 8642928, should be used until current service stock is depleted.
SERVICE PARTS INFORMATION:
Part No. Description
8663995 THM 700-R4 - Governor Drive Gear
and Pin Package
8629977 THM 400 - Govemor Drive Gear and
Pin Package
SERVICE MANUAL REFERENCE:
Refer to the appropriate 1988 Unit Repair Service Manual sections for removal and installation procedures not covered in this bulletin.
Labor Op: K6430 - Governor Assembly - R&R or Replace
Labor Time: .8 hrs - All Models