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The SON-28756-25K is the Sonnax “Smart Tech” Powerglide high gear drum designed to handle up to a 10-clutch disk pack and features additional apply area to provide great lockup and holding power. By redesigning the drum cavity and the piston, Sonnax was able to both increase the piston OD and decrease the piston ID to achieve 35% more apply area for this setup. What this means is the apply / holding force is dramatically increased. (Apply Force = Fluid Pressure X Piston Apply Surface Area). This gives the builder the ability to produce higher apply force on the clutch pack without increasing transmission line pressure.
This drum kit includes the Patented drum that is pre-machined for pump to high gear drum thrust washer, a PTFE coated drum to pump bushing, needle bearing drum to pump thrust washer, coated 6061 billet aluminum piston with seals, aftermarket return spring kit (springs, retainer & retainer clip) and a forged chromoly clutch hub designed to handle up to 10 clutch disks.
The drum can handle up to a 10-clutch disk setup but can be built with less clutch disks if the builder would prefer by simply adding in a combination of additional steels to provide the correct clutch pack clearance.
Tech Note: This drum does utilize a unique set of inner and outer piston lip seals which are not included in most standard overhaul kits. For reference the inner lip seal is part number SON-28756-07 and the outer lip seal is part number SON-28765-08.
