2-1 COAST DOWN CLUNK GEAR/OUTPUT SHAFT INFORMATION

MODELS AFFECTED: ALL 1983 THRU EARLY 1985 THM 200C TRANSMISSIONS

Some 1983 thru early 1985 model THM 200C transmissions may experience a 2-1 coastdown clunk condition. This condition occurs as the transmission shifts to first gear just before the car stops.

This condition can be repaired as follows:

1. Check engine idle speed and set to specifications.

2. On 1984 and early 1985 THM 200C transmissions built prior to Julian date 268 remove the valve body spacer plate. Drill the 2nd and 3rd clutch exhaust orifice out to 3.57 m (9/64"). Emery cloth both sides of the hole, slightly, to remove burrs and rough edges (Figure 2). Also remove the primary spring from the governor assembly (Figure 1). The 1983 THM 200C transmissions have the larger (9/64") orifice hole and will require onlyy the removal of the primary governor spring.

In some cases the above "on car" procedure may not repair this condition; it will then be necessary to remove the transmission and perform the following procedure:

1. Replace the rear internal gear and output shaft with part number 8633910. This service package will have the rear internal gear pressed onto the output shaft.

NOTICE: The OI and OU model THM 200C transmissions already have the press fit rear internal gear and output shaft and do not require replacement on these models. Reduce end play only as indicated in Step #2.

2. Upon reassembly of the transmissim, reduce the rear end play to .10mm - .38mm (.004 - .015 inches) by using a thicker selective washer, if required. If the 2-1 coastdown clunk is still to harsh after performing these above repairs check the rear differential back lash and correct if necessary.

NOTICE: Do not let rear end play get lower than .004 inches. Transmission damage may result.

Refer to the appropriate service manual for proper procedures not stated above.

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.