TORSIONAL RATTLE/RING NOISE TCC ENGAGES LIGHT THROTTLE

VEHICLES AFFECTED: 1983-85 S/T With 2.8L Engine and THM 700-R4 Transmission

Some 1983 - 1985 S/T trucks equipped with the 2.8L V-6 engine and THM 700-R4 automatic overdrive transmission may experience a torsional rattle or ringing type of noise when the torque converter clutch (TCC) engages at light throttle application below 40 mph.

This condition, which is torgue converter clutch/drivetrain related, nay be improved by increasing the TCC engagement speed. A TCC throttling valve, service kit P/N 8642970, is available to increase the TCC engagement speed to 40 - 45 mph.

Included in the service kit are:

TCC Throttling Valve TCC Throttling Valve Sleeve TCC Throttling Valve Spring Instruction Sheet

The installation of the service kit required removal and partial disassembly of the transmission valve body (Figure No. 1). Follow the instructions included with the service kit.

If additional dampening of torsional noise is necessary, some improvement may be obtained by filling the propshaft with urethane foam following the procedure listed below:

1. Obtain a urethane foam dispensing system, Insta-Foam Product's Model No. 9.5 Froth Pak kit (or equivalent) which is a small volume kit complete with all the required chemicals, dispensing equipment and instructions. A maximum of one (1) Froth Pak Kit will be required to foam-fill a propshaft from a long wheel base vehicle such as a Suburban or Pickup.

2. Remove propshaft from vehicle.

3. Wrap and tape U-joints with cloth.

4. After pivoting U-joints to allow an angled drill bit access to face of yoke, drill a 21/64 inch hole in face of each end yoke. Use caution not to damage U-joint seals (Figure No. 2).

5. Following directions and observing caution notes on kit, fill propshaft with spray foam from the top hole while maintaining propshaft in vertical position.

WHEN FOAN BEGINS TO OOZE OUT OF APPLICATION HOLE PAST THE NOZZLE, ENOUGH FOAM HAS BEEN DISPENSED. TO PREVENT SPEWING OF FOAM ON OPERATOR, PART, ETC DO NOT REMOVE NOZZLE FROM YOKE UNTIL FOAMING ACTIVITY SUBSIDES AND SET-UP BEGINS.

6. Allow foam to set, then remove U-joint cloth cover.

7. Drill out each end yoke hole and plug with silicone RTV rubber adhesive sealant (hi-heat resistance).

8. Reinstall propshaft assembly in vehicle.

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.