NEW DESIGN FORWARD CLUTCH SMOOTHER ENGAGEMENT - ALL 200C

MODELS AFFECTED: All 1984-87 THM 200C (MV9) EQUIPPED VEHICLES (EXCEPT FOR 1984-85 CZ, AND JY MODELS)

BULLETIN COVERS

1987 THM 200C transmissions are being built with a new design "feed/bleed" system for the forward clutch. This system gives more cushioning during forward clutch apply, and can be used on certain past models to reduce a harsh PARK/NEUTRAL to DRIVE engagement feel.

DATE OF PRODUCTION CHANGE: (Figures 1 and 2) ------------------------- August 4, 1986 (Julian date 216), these changes were introduced for all THM 200C models:

Forward Clutch Assembly, minus Check Ball in housing (619) Forward Clutch Piston Assembly (623) Additional waved plate (627) Front Internal Gear (636)

SERVICE ACTION

1984-87 models built before August 4, 1986 (Julian Date 216): If a vehicle equipped with a THM 200C transmission listed in SERVICE PARTS INFORMATION has a harsh PARK/NEUTRAL to DRIVE engagement, install the Neutral Drive Shift Package.

1987 models built on or after August 4, 1986 (Julian date 216)

Models built after implementation of the feed/bleed system can be serviced with individual parts.

IMPORTANT: When servicing the forward clutch, select the correct backing plate (627). Backing plate selection affects piston travel, shift feel and clutch durability.

Backing Plate Selection (Clutch fully assembled): Apply an evenly distributed load in the direction indicated in Figure 3 to remove slack from the clutch assembly. Use 20 lbs. (9kg) of pressure against the backing plate--excessive pressure will cause an inaccurate measurement. With the clutch assembly compressed, use a feeler gage to measure the distance between the backing plate and snap ring. Correct backing plate travel is 0.7mm-1.5mm (0.028"-O.059").

SERVICE PARTS INFORMATION

1984-87 models (excluding 84-85 CZ, JY) built before August 4, 1986 (Julian date 216):

PART NUMBER DESCRIPTION ----------- ------------ 8638957 Neutral Drive Shift Package (Contains Forward Clutch Assembly, Complete; Front Internal Gear and Thrust Washer)

1987 models built on or after August 4, 1987 (Julian date 216):

8648720 Forward Clutch Assembly, Complete 8638956 Forward Clutch Housing Package 8648721 Forward Clutch Piston 8657267 Backing Plate, Selective--Identification 7 (Figure 4) 8657266 Backing Plate, Selective--Identification 6 (Figure 4) 8657618 Backing Plate, Selective--Identification X (Figure 4) 8657265 Backing Plate, Selective--Identification 5 (Figure 4) 8657264 Backing Plate, Selective--Identification 4 (Figure 4) 8639947 Front Internal Gear and Thrust Washer Package

SERVICE NOTES

Earlier design front internal gears (Service Package Number 8630909) cannot be used with THM 200C models built after August 4, 1986 (Julian date 216).

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.