How to Install a Lock Up Switch on a 3T40

Engineered for light duty vehicles, the 3T40 is a three-speed automatic transmission installed in 1980 to 1995 model year General Motors vehicles. Designed to increase fuel economy, the 3T40 employs an internal electronic solenoid switch that automatically locks the transmission torque converter in place at high speeds. If the transmission becomes overworked or overheated, the lockup switch will often fail, requiring removal of the transmission from the vehicle for repair.

Instructions

1

Park the vehicle in a level spot, and block both rear wheels with wheel blocks. Place the transmission in neutral, and set the parking brake.

2

Lift the front end of the vehicle, with a floor jack. Place a jack stand under each side of the front axle, adjacent to the wheels.

3

Move the floor jack under the transmission, and adjust the jack to support the transmission casing.

4

Push the tab on the solenoid lockup switch plug, attaching the wires at the front of the transmission with your finger, and pull the plug apart with your hands.

5

Disconnect the transmission torque converter from the engine flywheel, the transmission housing from the engine block and the transmission casing from the transmission mount with a wrench. Lower the transmission with the jack.

6

Unbolt the torque convertor from the transmission with a wrench, and work the converter free from the transmission with your hands.

7

Remove the access panel from the front of the transmission with a socket wrench. Disconnect the solenoid lockup switch, with a Phillips screwdriver, and install the new lockup switch in the same orientation as the old switch. Reattach the access panel to the front of the transmission with the wrench.

8

Slide the torque converter into the transmission with your hands, so the converter rests firmly against the front of the transmission. Apply heat-resistant thread-sealer to the torque converter mounting bolts. Install the converter bolts finger-tight, and then tighten the bolts in place with a torque wrench to the 38 foot-pound torque setting.

9

Apply thread sealer to all mounting bolts, and reconnect the transmission to the transmission mount, the transmission housing to the engine block and the transmission to the engine flywheel with a wrench. Tighten the transmission mounting bolts to the transmission mount with the torque wrench to the 30 foot-pound torque setting. Plug in the solenoid lockup wires.

10

Remove the vehicle from the jack stands with the floor jack.