Super Hold Servo Kit

Part No.


Super Hold Servo Kit
  • Super Hold Servo Kit



Super Hold Servo Kit

Part No. 28821-09K

  • Servo Assembly
  • Cover Gasket
  • Case-to-Cover O-Ring
  • Servo Pin Seals (2) PTFE, 1 extra
  • Primary Piston Seals (2) PTFE
  • Return Spring

Sonnax super hold servo kit 28821-09K dual piston design has 30% more apply area than the OE Powerglide servo. The patented design fits completely inside the case, and the 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.

  • 30% More apply area
  • Allows line pressure to be reduced, freeing up horsepower
  • Dual seals for piston to case bore
  • Pin-to-case PTFE seal
  • Fits into the same space as a standard servo assembly
  • Patent No. 5,944,627

Related Parts

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Prevent "Mystery" Powerglide Band Failures by Overcoming the Servo Pin Bias Effect

Unexplained band failure in Powerglides is a common problem that can be overcome by understanding the servo pin bias effect. This video demonstrates how the servo performs at high pressures when fitted with an OE, light aftermarket or Sonnax race-calibrated spring, available as a standalone component or in Sonnax 28821-20K. The video dramatically shows the pin bias effect in action, and why overcoming this built-in design flaw of the Powerglide servo is the only way to prevent “mystery” band failures.

Learn more about the servo pin bias effect.

Contact a Sonnax Distributor to purchase this part.