Supported Servo Master Kit
Part No. 28821-20K
Conventional GM Powerglide servos are not well-supported and the return springs do not function properly, both leading causes of band failure. Sonnax supported servo master kit 28821-20K is an all-in-one kit that eliminates piston binding and includes a race-calibrated spring to counteract the pin bias effect.
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 supported pin design of this Sonnax kit eliminates friction caused by side-loading and ensures the servo piston will apply and release without binding.
"Mystery" band failures are a common result of aftermarket servo return springs and weak OE springs prone to collapse that do not reliably release the servo. The Sonnax spring in this kit is race-calibrated to ensure consistent servo function for longer band life and a cooler transmission. The spring's higher seat pressure helps ensure full servo release, but also features a lower spring rate to prevent excessive release force in the apply position.
- Unique cover and pin combination eliminates piston binding that causes unexplained band failure
- Race-calibrated spring counteracts pin bias effect up to 275 psi
- Dual PTFE seal rings for better seal and low friction
- OE apply area
- Low-profile design ensures adequate clearance
- 6061 Anodized billet aluminum cover
- Supported Servo Cover
- Supported Servo Pin
- Servo Piston
- Return Spring
- Retaining Clip
- Cover O-Ring
- Pin O-Rings (2) 1 extra
- Drain Plug Not shown
- Bolts (3) Not shown
- Pin Shims (3)
- Spring Shims (2)
- PTFE Piston Seal Rings (2)