28821-09K Powerglide Super Hold servo piston kit Sonnax 28821-09K

Features

Sonnax super hold servo assembly 28821-09K dual piston design has 30% more apply area
than the original servo. The patented design fits completely inside the case; external cover
clearance is the same as original servos. The larger apply area will increase band apply force at
your current line pressure or allows you to reduce line pressure by 20% to 30% while maintaining
the same apply force. Improved sealing throughout reduces fluid loss and is optimized
for low friction movement. Powerglide servos have some residual apply pressure in high gear
when the servo is released. At higher pressures this residual pressure can overcome the return
spring, resulting in the band not releasing fully, robbing power in high gear and burning the
band. The return spring in the Sonnax servo is tunable, to ensure full servo release even at
higher line pressures.