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Servo Piston & Cover Kit
Part No. 28821-04K

O-Ring Type, Purple Anodized

View Instructions

Sonnax servo cover kits 28821-03K and 28821-06K are designed to replace other covers and require no modifications to the case. They can be installed with servo piston kits 28821-01K or 28821-02K. Sonnax master servo kits 28821-04K and 28821-07K are designed to replace the piston and cover and require no modifications to the case.

The kits feature the no leak dual O-ring servo using two O-ring seals for superior, positive sealing. In applications with a distorted bore or case flex, O-rings will conform to the bore surfaces, a feature not possible with metal sealing rings. Precise slip fit with apply pin further improves performance.

In addition, Sonnax master servo kits 28821-05K and 28821-08K are designed to replace the piston and cover and accept either two PTFE seal rings or two OE metal sealing rings. Made with the same high-quality billet aluminum as our dual O-ring servos, these servos will give you the positive apply needed in high pressure racing conditions.

  • Better sealing with O-ring and gasket
  • Direct replacement
  • Fitting for pressure testing
  • Stronger to handle higher pressure
  • Cover Purple Anodized
  • Pipe Plug
  • Servo Piston
  • O-Rings (2)
  • Hex Head Bolts (3)
  • O-Ring
  • Gasket
  • 28821 04k