Although General Motors produced the Powerglide transmission, it is most commonly associated with Chevrolet. Within the transmission is a steel band that holds a gear within the transmission stationary. Over time, the surface of the band wears down. When this occurs, the transmission will noticeably slip when it shifts from low gear to high gear. Because the band wears down, you need to periodically adjust it.
Basic Operation
The Powerglide consists primarily of a gear box and a torque converter. Within the gear box is a two-speed planetary gear set. The shift from the low gear to the high gear is automatic. A governor driven by the output shaft interacts with a throttle valve connected to the accelerator pedal, to determine when the shift occurs.
Accessing the Adjusting Screw
The band's adjusting screw is on the driver's side of the transmission. For most vehicles, accessing the screw does not present a problem once the vehicle is up on jack stands. On Corvette models, it may be necessary to drop the driver's side exhaust pipe to access the screw. On Chevelles it may be necessary to remove the transmission's crossmember and the rear mount bolts, and move the transmission slightly toward the passenger's side of the vehicle.
Releasing the Adjusting Screw
Note that a nut surrounds the top of the band's adjusting screw. This nut is called a locknut and is designed to prevent the screw from falling out of adjustment. To adjust the screw, first release the locknut. Turn the locknut 1/4 turn in a counterclockwise direction with an open-end wrench. Hold the locknut in place while turning the adjusting screw. The 1/4 turn is not an approximate figure; it must be exact.
Adjusting the Band
Adjust the band by turning its adjusting screw with a torque wrench. Tighten the screw to 70 inch-pounds of torque. If the band has been used for 6,000 miles or more, turn the screw in a counterclockwise direction four complete revolutions, then tighten the locknut. If less than 6,000 miles, turn the screw three complete revolutions, then tighten the locknut.
