A/T - Sporadic Engagement of Torque Converter Clutch
88chevy11Number: 88-207-7A
Section: 7A
Date: MAY, 1988
Subject: SPORADIC ENGAGEMENT OF
TORQUE CONVERTER CLUTCH
Model and Year: 1980-88 MODELS WITH COMPUTER COMMAND
CONTROL AND AUTOMATIC TRANSMISSION/ TRANSAXLE AND CABLE DRIVEN SPEEDOMETER
TO: ALL CHEVROLET DEALERS
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 a scanner). Customers may describe this condition as momentary loss of power or engine miss at 30-40 mph.