SPORADIC ENGAGEMENT OF THE TORQUE CONVERTER CLUTCH

MODELS AFFECTED: ALL 1980-88 MODELS WITH CCC AND/OR EFI WITH CABLE DRIVEN SPEEDOMETERS

Sporadic engagement and disengagement of the converter clutch may be caused by a bent or kinked speedometer cable. This condition may occur with cluster speed sensor systems. A cluster speed sensor system has a cable from the transmission to the cluster to drive the speedometer needle. In addition, the signal from the cable is buffered in the cluster and then sent to the ECM. The ECM has certain fixed values for minimum lock and unlock speeds which typically center around 30-40 mph.

If the speedometer cable is kinked/bent, an inconsistent speed signal will be passed through the buffer and sent to the ECM. The ECM will interpret the varied speed signals as actual vehicle speed changes. If a variation in speed signals occurs at 30-40 mph, the correct criteria could be met in the ECM such that the ECM would command the torque converter to lock and unlock. (This condition can be verified by using an ALDL Scan Tool.) Customers may describe this condition as momentary loss of power or engine miss at 30-40 mph.

NOTICE: The above information is applicable through the 1988 model year only for the models using cable driven speedometers.

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.