Band Apply Servo: Description and Operation

Front Servo
The front servo applies the 2nd overrun band to provide engine braking in 2nd gear and 1st gear. It is also used as an accumulator for the apply of the direct clutch, and in conjunction with a series of check balls controlling orifices, is a part of the timing for the release of the direct clutch.

To prevent the apply of the 2nd overrun band in Neutral, Direct Drive and Reverse ranges, oil is directed from the manual valve to the release side of the servo piston.

In Direct Drive the servo release oil from the manual valve is used to charge the servo in preparation for the apply of the direct clutch.

Direct clutch oil is directed to the front servo accumulator piston where spring force plus direct clutch pressure stroke the piston up a against the force of servo release oil. This lowers the clutch apply pressure for a smooth engagement.

The release of the direct clutch and the exhausting of the front servo accumulator is slowed down by three check balls and three orifices which permits a soft return of the drive load to the intermediate sprag and also allows engine RPM to increase during a detent 3-2 downshift in preparation for the lower gear ratio, which results in a smooth shift and better acceleration.

Rear Servo
The rear servo applies the rear band for overrun engine braking in low range 1st gear. It applies the band in Reverse to hold the reaction carrier to provide reverse gear ratio.