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Supported Servo Master Kit

Supported Servo Master Kit

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Availability: In stock


Quick Overview



Supported Servo Cover
Supported Servo Pin
Servo Piston
PTFE Piston Seal Rings (2)
Return Spring
Spring Shims (2)
Pin Shims (2)
Retaining Clip
Bolts (3) Not shown
Drain Plug Not shown
Pin O-Rings (2) 1 extra
Cover O-Ring
Sonnax supported servo master kit 28821-20K includes everything needed for the Powerglide servo: Sonnax supported servo pin and cover, race-calibrated servo return spring and dual PTFE seal servo piston kit.

Conventional Powerglide servos are not well-supported. At high apply pressures or with a worn servo pin bore, the servo piston is side-loaded in the case, causing friction and binding of the piston. The unique Sonnax supported servo master kit eliminates friction caused by side-loading and ensures the servo piston will apply and release without binding. The servo return spring is the source of many "mystery" band failures caused by inconsistent servo release and weak springs prone to collapse. Sonnax race-calibrated servo return spring ensures optimum servo function in high gear for longer band life, cooler transmission and tunability of shift. The Sonnax servo spring has higher seat pressure to help ensure full servo release but with a lower rate for greater net apply force. The high strength billet aluminum piston features dual PTFE seals.

Unique cover design eliminates piston binding that causes unexplained band failure
Spring designed to work with line pressures from 200–275 psi
Dual PTFE seal rings for better seal and low friction

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