#3. C4 high performance servo. As used with Shelby Mustang and other performance vehicles, a “C” ratio servo offers greater holding power, giving cleaner, firmer 1-2 and 2-3 shifts. Machined from 6061 aluminum billet, this servo features superior sealing over a wide range of fluid pressure. This is the largest in the C4 servo family and works equally well in Performance C5 applications too. The servo pin incorporates two (2) Teflon sealing rings to insure the hydraulic integrity of the pin in worn cases. Cleaning up a 2-3 flare was never easier than installing this servo.